Patent Application
20110187419
The disclosure of Japanese Patent Application No. 2010-21471 filed on Feb. 2, 2010 including the specification, drawings, and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a semiconductor integrated circuit and a voltage controller therewith, and more particularly, to a semiconductor integrated circuit that detects the characteristics of a chip.
2. Description of Related Art
The power consumption of a semiconductor integrated circuit using a complementary metal oxide semiconductor (CMOS) logic gate can be reduced, for instance, by dynamic voltage and frequency scaling (DVFS). DVFS is a technique for controlling a supply voltage in accordance with a demanded operation speed. DVFS can be implemented by using a delay monitor. The delay monitor detects whether the operation speed of a chip has reached a reference value. Therefore, the delay monitor needs to accurately detect the characteristics of the chip that are dependent on process level, temperature, and supply voltage.
A semiconductor integrated circuit using a delay monitor is disclosed in Japanese Unexamined Patent Publication No. 2008-180635. The delay monitor includes a ring oscillator and counts the number of oscillations of the ring oscillator during a predetermined period. Thus, a semiconductor integrated circuit based on a conventional technology can detect gate delay with the delay monitor and without using a temperature sensor or a voltage sensor. In other words, the semiconductor integrated circuit based on the conventional technology can detect variations in the characteristics of an element in a chip with the delay monitor.
A semiconductor integrated circuit using a monitor circuit or a speed monitor circuit is disclosed in Japanese Unexamined Patent Publications No. 2002-100967 and 2005-045172.
For example, the conventional technology outputs average variations in the characteristics of an element in a chip by averaging the output results (counts) of plural delay monitors (monitor circuits) disposed in the chip. Particularly, the conventional technology can easily detect the characteristics of the chip because it causes the delay monitors to output resulting digital values (counts).
In order to detect the characteristics of the chip with high accuracy, the delay monitors need to perform a counting operation at the same time. More specifically, the ring oscillators in the delay monitors need to oscillate at the same time. Therefore, control signals (oscillator enable signals) supplied to the delay monitors to control the oscillation time of the ring oscillators need to have the same ON period. As such being the case, the conventional technology handles a one-clock cycle of a reference clock as the ON period in order to avoid the influence of a skew between the rise and fall of the control signals.
When the conventional technology is used, the ON periods of the control signals are determined in accordance with the reference clock and a measurement start signal. More specifically, during the use of the conventional technology, a control signal (oscillator enable signal) in the ON state is generated by allowing a flip-flop to detect a high-level measurement start signal in synchronism with the reference clock. As described above, when the conventional technology is used, two signal wires handling the reference clock and the measurement start signal are used in each delay monitor to generate a control signal. Therefore, if there is a significant skew between the reference clock and the measurement start signal, the control signals supplied to the individual delay monitors may differ in the ON period. That is why the conventional technology cannot accurately detect the characteristics of the chip.
According to an embodiment of the present invention, there is provided a semiconductor integrated circuit including a first monitor circuit and a control circuit. The control circuit generates a control signal having M successive pulses (M is 2 or a greater integer) and outputs the control signal to the first monitor circuit. The first monitor circuit includes a frequency divider circuit and an oscillator circuit. The frequency divider circuit frequency-divides the control signal by M and generates the resulting signal as an enable signal. The oscillator circuit generates an oscillation signal as a monitor output value during a period defined in accordance with the enable signal.
As the above-described circuit configuration is employed, the characteristics of a chip can be accurately detected.
The present invention makes it possible to provide a semiconductor integrated circuit that is capable of accurately detecting the characteristics of a chip.
Embodiments of the present invention will be described in detail based on the following figures, wherein:
Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. For clarity of explanation, redundant descriptions will be omitted as appropriate.
The control circuit 13 inputs a clock signal CLK0 and a control signal RCTRL, and outputs a reset signal RE and a clock pulse signal EN_PULSE to the monitor circuits 12_1 to 12_N. The monitor circuits 12_1 to 12_N output their respective counts C_1 to C_N to the summing circuit 14. The summing circuit 14 outputs an average count CAVE, which is the average of the counts C_1 to C_N. The monitor circuits 12_1 to 12_N are adapted to detect the characteristics of a chip that are dependent on process level, temperature, and supply voltage.
The counter 132 counts detected edges (e.g., rising edges) of the clock signal CLK1, and outputs the obtained count to the logic circuit 133. The logic circuit 133 generates the reset signal RE and the clock pulse signal EN_PULSE in accordance with the count, and outputs the generated signals to the monitor circuits 12_1 to 12_N (see
The frequency divider 121 frequency-divides the clock pulse signal EN_PULSE by two to obtain an enable signal EN, and outputs the obtained enable signal EN to the ring oscillator 122.
The ring oscillator 122 oscillates only during a period T during which the enable signal EN is at a high level (=1), and outputs an oscillation signal ROOUT. More specifically, the enable signal EN is input to one input terminal of the NAND 125 in the ring oscillator 122. An output signal of the NAND 125 is input to the other input terminal of the NAND 125 through the delay gate 124. The ring oscillator 122 then outputs an output signal of the delay gate 124 to the counter 123 as the oscillation signal ROOUT. The delay gate 124 includes, for instance, plural inverters that are serially coupled. Here, the delay gate 124 needs to sufficiently reduce the influence of random variations in the characteristics of the individual inverters upon delay time. Therefore, the number of inverters included in the delay gate 124 is limited so that the delay time remains unaffected.
The counter 123 is initialized to a count of 0 by the reset signal RE before the enable signal EN is set to 1. Subsequently, the counter 123 counts the oscillations (pulses) of the oscillation signal ROOUT during the period T during which the enable signal EN is 1, and outputs a count C_i.
As described earlier, the monitor circuits 12_1 to 12_N shown in
The averaging circuit 142 receives the result of addition performed by the final adder 14_N−1, and outputs bits starting at the (k+1)th low-order bit position and ending at the (k+m)th lower-order bit position of the received result.
An operation of the semiconductor integrated circuit 11 according to the present embodiment will now be described with reference to a timing diagram of
The counter 123 counts the oscillations of the oscillation signal ROOUT during the period T, and outputs the resulting count C_i. Here, the count C_i indicates a count T/TROSC that corresponds to the oscillation cycle TROSC of the ring oscillator 122 (at time t4).
As mentioned above, the monitor circuits 12_1 to 12_N output their respective counts C_1 to C_N to the summing circuit 14. The summing circuit 14 then averages the counts C_1 to C_N and outputs the resulting average value (C_1+C_2+ . . . +C_N)/N as the average count CAVE.
As described above, the semiconductor integrated circuit according to the present embodiment can detect an average value representing the variations in the characteristics in a chip by using the monitor circuits disposed at plural locations within the chip. Here, the semiconductor integrated circuit according to the present embodiment controls the oscillation time of the ring oscillator included in each monitor circuit by using the clock pulse signal EN_PULSE alone. Therefore, the semiconductor integrated circuit according to the present embodiment differs from those based on the conventional technology in that the oscillation time of the ring oscillator does not vary due to a significant skew between two control signals (e.g., the reference clock and measurement start signal based on the conventional technology). In other words, the semiconductor integrated circuit according to the present embodiment ensures that the ring oscillators in the monitor circuits precisely agree in oscillation time. Consequently, the semiconductor integrated circuit according to the present embodiment can monitor the performance of the chip with high accuracy.
Further, the semiconductor integrated circuit according to the present embodiment can control the frequency division ratio n of the cycle T0 of the clock signal CLK0 by using the frequency divider 131 included in the control circuit 13. Therefore, the oscillation time of the ring oscillator 122 included in each monitor circuit can always be set within a desired range without regard to the cycle T0 of the clock signal CLK0. Consequently, the semiconductor integrated circuit according to the present embodiment can evaluate the performance of chips having different operating frequencies by using the monitor circuits having the same circuit configuration.
In the present embodiment, it is assumed that N is the k-th power of 2. However, N need not always be the k-th power of 2. Alternatively, N may be any natural number. If N is a natural number other than the k-th power of 2, a complex circuit configuration results because the summing circuit 14 needs to additionally include a divider having a divisor of N. However, the versatility of the monitor circuits will be increased. If N is equal to 1, the summing circuit 14 need not be used; therefore, the circuit configuration need not include the summing circuit 14 as indicated in
In the present embodiment, it is assumed that the monitor circuit 12_i shown in
While the enable signal EN is 1, the monitor circuit 12b_i does not output the count of the counter 123 as the count C_i, but outputs a value of 0. When the enable signal EN changes from 1 to 0, the monitor circuit 12b_i outputs a final count of the counter 123 as the count C_i. This circuit configuration ensures that the count C_i reached during the oscillation of the ring oscillator 122 (during the period T) is not output, as indicated in
In the present embodiment, it is assumed that the frequency divider 121 frequency-divides the clock pulse signal EN_PULSE by two to generate the enable signal EN. However, the present invention is not limited to the use of such an enable signal generation method. The present invention can also be applied to a circuit configuration in which all the pulses R of the clock pulse signal EN_PULSE are input to generate the enable signal EN while the frequency division ratio of the frequency divider 121 is R (R is a natural number).
In the present embodiment, it is assumed that the control circuit 13 outputs the same clock pulse signal EN_PULSE to the monitor circuits 12_1 to 12_N. However, the present invention is not limited to the use of such a circuit configuration. The present invention can also be applied to a circuit configuration in which the control circuit 13 outputs different clock pulse signals EN_PULSE_i (i is an integer between 1 and N) to the monitor circuits 12_1 to 12_N. In this instance, the average count CAVE of a longer sampling period can be detected by generating the clock pulse signals EN_PULSE_i in such a manner that the ring oscillators 122 included in the monitor circuits 12_1 to 12_N do not oscillate at the same time. This makes it possible to detect the characteristics of a chip that prevail during a longer sampling period.
In the present embodiment, it is assumed that the monitor circuit 12_i shown in
The above-described circuit configuration makes it possible to decrease the frequency of the frequency-divided signal DIVOUT to a desired value even when the oscillation frequency of the ring oscillator 122 is high. This permits the counter 123 to lower the upper limit of its count. Thus, the bit width of the output signal can be decreased. It means that the number of digits required for the counter 123 can be decreased. Further, even when the cycle T0 of the clock signal CLK0 is excessively long, the bit width of the output signal of the counter 123 can be decreased by increasing the frequency division ratio a. In other words, the number of digits required for the counter 123 can be decreased.
When, for instance, the cycle T0 of the clock signal CLK0 is short, the frequency division ratio n of the frequency divider 131 is increased as shown in
The control circuit 23 inputs the clock signal CLK0 and the control signal RCTRL, and outputs reset signals RE_1 to RE_N and clock pulse signals EN_PULSE_1 to EN_PULSE_N to the associated monitor circuits 22_1 to 22_N. The monitor circuit 22_1 outputs a count C2_1 to the monitor circuit 22_2. The monitor circuit 22_2 outputs a count C2_2 to the monitor circuit 22_3. In this manner, the monitor circuits 22_1 to 22_N−1 output counts C2_1 to C2_N−1 to the succeeding monitor circuits 22_2 to 22_N, respectively. The monitor circuit 22_N outputs a count C2_N to the averaging circuit 242. The averaging circuit 242 outputs an average count C2AVE, which is the average value of the counts C2_1 to C2_N. It should be noted that the monitor circuits 22_1 to 22_N are adapted to detect the characteristics of a chip that are dependent on process level, temperature, and supply voltage.
The control circuit 23 will not be described in detail because it has the same circuit configuration as that of the control circuit 13 except that the former outputs different reset signals RE_1 to RE_N and clock pulse signals EN_PULSE_1 to EN_PULSE_N to the monitor circuits 22_1 to 22_N. The control circuit 23 outputs the clock pulse signals EN_PULSE_1 to EN_PULSE_N, which each include two pulse signals.
The frequency divider 221 frequency-divides the clock pulse signal EN_PULSE_i by two, and outputs the resulting frequency-divided signal to the ring oscillator 222 as the enable signal EN.
The ring oscillator 222 oscillates only during the period T during which the enable signal EN is at a high level (=1), and outputs the oscillation signal ROOUT. The ring oscillator 222 will not be described in detail here because it has the same circuit configuration as that of the ring oscillator 122 according to the first embodiment. The NAND 225 corresponds to the NAND 125, and the delay gate 224 corresponds to the delay gate 124.
The counter 223 is set to a count C2_i−1 of the preceding monitor circuit 22_i−1 by a reset signal RE_i before the enable signal EN is set to 1. In the case of the monitor circuit 22_1 (when i=1), the counter 223 is initialized to a count of 0 by a reset signal RE_1 before the enable signal EN is set to 1. Subsequently, the counter 223 counts the oscillations (pulses) of the oscillation signal ROOUT during the period T during which the enable signal EN is 1, and outputs the sum of the resulting count and a count C2_i as the count C2_i.
The monitor circuit 22_N outputs the sum of the counts reached by the monitor circuits 22_1 to 22_N to the averaging circuit 242 as the count C2_N. The averaging circuit 242 divides the count C2_N by N and outputs the resulting value as the average count C2AVE. The counts C2_N, C2AVE are both binary values. When the number N of monitor circuits is equal to the k-th power of 2, the averaging circuit 242 functions as a shifter that shifts the count C2_N toward least significant bit positions by k bits and outputs the (k+1)th least significant bit and higher-order bits.
An operation performed by the semiconductor integrated circuit 21 according to the present embodiment will now be described with reference to a timing diagram of
First of all, an operation of the monitor circuit 22_1 will be described with reference to the timing diagram of
An operation of the monitor circuit 22_2 will now be described with reference to the timing diagram of
Subsequently, the same operation is performed in the monitor circuit 22_i (i=3, 4, N) as in the monitor circuit 22_2. When the reset signal RE_i is 1, the counter 223 of the monitor circuit 22_i is set to the count C2_i−1. The count C2_1 reached upon completion of counting by the monitor circuit 22_i is expressed by Equation (1) below:
Upon completion of counting (at time te), the monitor circuit 22_N outputs the count C2_N to the averaging circuit 242. The averaging circuit 242 divides the count C2_N by N and outputs the resulting value C2_N/N as the average count C2AVE. In other words, the averaging circuit 242 divides the count C2_N by N and outputs the resulting value C2_N/N as a final monitor output value.
As described above, the semiconductor integrated circuit according to the present embodiment can detect an average value representing the variations in the characteristics in a chip by using the monitor circuits disposed at plural locations within the chip. Here, the semiconductor integrated circuit according to the present embodiment controls the oscillation time of the ring oscillator included in each monitor circuit by using the associated clock pulse signal EN_PULSE alone. Therefore, like the semiconductor integrated circuit according to the first embodiment, the semiconductor integrated circuit according to the present embodiment ensures that the ring oscillators included in the monitor circuits precisely agree in oscillation time. Consequently, the semiconductor integrated circuit according to the present embodiment can monitor the performance of the chip with high accuracy. Further, in the semiconductor integrated circuit according to the present embodiment, all the outputs of the monitor circuits need not be coupled to the summing circuit 24. In other words, the semiconductor integrated circuit according to the present embodiment is configured by merely coupling the output of each monitor circuit to a neighboring monitor circuit. This makes it possible to reduce the overall wiring length.
In the present embodiment, the summing circuit 24 divides the count C2_N by N and outputs the resulting value C2_N/N as the monitor output value. However, the present invention is not limited to the use of such a circuit configuration. The present invention can also be applied to a circuit configuration in which the count C2_N is output as the monitor output value instead of the count C2_N/N. If such an alternative circuit configuration is employed, the averaging circuit 242 is not required.
The control circuit 33 inputs the clock signal CLK0 and the control signal RCTRL, outputs the reset signal RE and an s-bit select signal SEL to the summing circuit 34, and outputs the clock pulse signal EN_PULSE to the monitor circuits 32_1 to 32_N. It should be noted that 2̂(s−1)<N<2̂s. The monitor circuits 32_1 to 32_N output their respective oscillation signals C3_1 to C3_N to the summing circuit 34. The summing circuit 34 outputs an average count C3AVE in accordance with the oscillation signals C3_1 to C3_N. The monitor circuits 32_1 to 32_N are adapted to detect the characteristics of a chip that are dependent on process level, temperature, and supply voltage.
The control circuit 33 will not be described in detail because it has the same circuit configuration as that of the control circuit 13 except that the former outputs the s-bit select signal SEL. Each time the value of the select signal SEL changes, the control circuit 33 outputs the clock pulse signals EN_PULSE, which includes two pulse signals.
The frequency divider 321 frequency-divides the clock pulse signal EN_PULSE by two, and outputs the resulting frequency-divided signal to the ring oscillator 322 as the enable signal EN.
The ring oscillator 322 oscillates only during the period T during which the enable signal EN is at a high level (=1), and outputs the oscillation signal ROOUT. The ring oscillator 322 will not be described in detail here because it has the same circuit configuration as that of the ring oscillator 122 according to the first embodiment. The NAND 325 corresponds to the NAND 125, and the delay gate 324 corresponds to the delay gate 124. The output buffer 326 drives the oscillation signal ROOUT and outputs it as an oscillation signal C3_i.
The averaging circuit 343 divides the total number of oscillations of the oscillation signals C3_1 to C3_N by N, and outputs the resulting value as the average count C3AVE. In other words, the averaging circuit 343 divides a count CNT_N by N and outputs the resulting value as the average count C3AVE. The values CNT_i and C3AVE are in binary notation. When the number N of monitor circuits is equal to the k-th power of 2, the averaging circuit 343 functions as a shifter that shifts the count CNT_i toward least significant bit positions by k bits and outputs the (k+1)th least significant bit and higher-order bits.
An operation performed by the semiconductor integrated circuit 31 according to the present embodiment will now be described with reference to a timing diagram of
In the monitor circuit 32_1, the counter 342 is initialized (for a period of time between t1 and t2) when the reset signal RE is 1. Subsequently, the first pulse signal of the clock pulse signal EN_PULSE rises (at time t3). Next, the second pulse signal of the clock pulse signal EN_PULSE rises (at time t4). In the monitor circuit 32_1, the frequency divider 321 outputs an enable signal EN of 1 during a period T between t3 and t4, that is, during a period between the instant at which the clock pulse signal EN_PULSE rises and the instant at which the same signal EN_PULSE rises again. The ring oscillator 322 oscillates during the period T and outputs the oscillation signal ROOUT to the output buffer 326. The output buffer 326 drives the oscillation signal ROOUT and outputs it as the oscillation signal C3_1. The counter 342 included in the summing circuit 34 counts the oscillations of the oscillation signal C3_1 during the period T, and outputs the resulting count CNT_1. Here, the count CNT_1 indicates a count T/TROSC1 that corresponds to the oscillation cycle TROSC1 of the ring oscillator 322 included in the monitor circuit 32_1 (at time t4).
Next, the value of the select signal SEL changes (at time t5). The selector 341 then selects an oscillation signal C3_2 and outputs it to the counter 342. After the select signal SEL is changed, the first pulse signal of the clock pulse signal EN_PULSE rises (at time t6). Subsequently, the second pulse signal of the clock pulse signal EN_PULSE rises (at time t7). The monitor circuit 32_2 outputs the oscillation signal C3_2 for a period T between t6 and t7. The counter 342 included in the summing circuit 34 counts the oscillations of the oscillation signal C3_2 during the period T, and outputs the sum of the resulting count and the count CNT_1 as a count CNT_2. In this manner, the counter 342 counts the oscillations of all oscillation signals C3_1 to C3_N and outputs the resulting count as the count CNT_N (at time te).
The count CNT_i reached when the counter 342 completes the counting of oscillation signals of up to C3_i is expressed by Equation (2) below:
The averaging circuit 343 divides the total count CNT_N of the oscillations of the oscillation signals C3_1 to C3_N by N and outputs the resulting value CNT_N/N as the average count C3AVE. In other words, the averaging circuit 343 divides the count CNT_N by N and outputs the resulting value CNT_N/N as a final monitor output value.
As described above, the semiconductor integrated circuit according to the present embodiment can detect an average value representing the variations in the characteristics in a chip by using the monitor circuits disposed at plural locations within the chip. Here, the semiconductor integrated circuit according to the present embodiment controls the oscillation time of the ring oscillator included in each monitor circuit by using the clock pulse signal EN_PULSE alone. Therefore, like the semiconductor integrated circuit according to the first embodiment, the semiconductor integrated circuit according to the present embodiment ensures that the ring oscillators included in the monitor circuits precisely agree in oscillation time. Consequently, the semiconductor integrated circuit according to the present embodiment can monitor the performance of the chip with high accuracy. Further, the area occupied by the semiconductor integrated circuit according to the present embodiment can be decreased because each monitor circuit does not need to include a counter.
In the present embodiment, the summing circuit 34 divides the count CNT_N by N and outputs the resulting value CNT_N/N as the monitor output value. However, the present invention is not limited to the use of such a circuit configuration. The present invention can also be applied to a circuit configuration in which the count CNT_N is output as the monitor output value instead of the count CNT_N/N. If such an alternative circuit configuration is employed, the averaging circuit 343 is not required.
The control circuit 43 inputs the clock signal CLK0 and the control signal RCTRL, and outputs a shift pulse signal SHIFT_PULSE and a control signal MODE to the monitor circuits 42_1 to 42_N and the summing circuit 44. Further, the control circuit 43 outputs the reset signal RE and the clock pulse signal EN_PULSE to the monitor circuits 42_1 to 42_N. The monitor circuit 42_1 outputs a register value REG_1 to the monitor circuit 42_2. The monitor circuit 42_2 outputs a register value REG_2 to the monitor circuit 42_3. In this manner, the monitor circuits 42_1 to 42_N−1 output register values REG_1 to REG_N−1 to the succeeding monitor circuits 42_2 to 42_N. The monitor circuit 42_N outputs a register value REG_N to the summing circuit 44. The summing circuit 44 outputs an average count C4AVE in accordance with the register values REG_1 to REG_N. The monitor circuits 42_1 to 42_N are adapted to detect the characteristics of a chip that are dependent on process level, temperature, and supply voltage.
The control circuit 43 will not be described in detail because it has the same circuit configuration as that of the control circuit 13 except that the former outputs the shift pulse signal SHIFT_PULSE and the control signal MODE. It should also be noted that the control circuit 43 outputs the clock pulse signals EN_PULSE, which includes two pulse signals.
The frequency divider 421 frequency-divides the clock pulse signal EN_PULSE by two, and outputs the resulting frequency-divided signal to the ring oscillator 422 as the enable signal EN.
The ring oscillator 422 oscillates only during the period T during which the enable signal EN is at a high level (=1), and outputs the oscillation signal ROOUT. The ring oscillator 422 will not be described in detail here because it has the same circuit configuration as that of the ring oscillator 122 according to the first embodiment. The NAND 425 corresponds to the NAND 125, and the delay gate 424 corresponds to the delay gate 124.
The counter 423 is a synchronous counter that includes plural flip-flops (e.g., m flip-flops) (not shown), the number of which corresponds to the bit width of an output signal (e.g., m bits). First of all, the counter 423 is initialized to a count of 0 by the reset signal RE before the enable signal EN is set to 1. Subsequently, when the control signal MODE is 0 (in a count mode), the counter 423 counts the oscillations of the oscillation signal ROOUT. More specifically, the counter 423 counts the oscillations (pulses) of the oscillation signal ROUT during the period T during which the enable signal EN is 1, and stores the resulting count C4_i in the internal flip-flops. A value stored in the flip-flops is referred to as a register value REG_i. In the count mode, therefore, the register value REG_i indicates the count C4_i. When, on the other hand, the control signal MODE is 1 (in a shift mode), each flip-flop fetches a value stored in a flip-flop corresponding the preceding monitor circuit 42_i−1 in synchronism with the shift pulse signal SHIFT_PULSE. More specifically, the j-th flip-flop (j is an integer between 1 and m) fetches a value stored in the j-th flip-flop in the preceding monitor circuit 42_i−1 in synchronism with the shift pulse signal SHIFT_PULSE.
In other words, when the control signal MODE is 1, the monitor circuit 42_i fetches a register value REG_i−1 output from the preceding monitor circuit 42_i−1 in synchronism with the shift pulse signal SHIFT_PULSE, and outputs the fetched register value to the monitor circuit 42_i+1 as the register value REG_i. When the control signal MODE is 1, the monitor circuit 42_N outputs the register value REG_N to the summing circuit 44. As described above, the monitor circuits 42_1 to 42_N switch between the count mode and the shift mode in accordance with the control signal MODE.
The averaging circuit 443 divides the count CNT_N by N, and outputs the resulting value as the average count C4AVE. When the number N of monitor circuits is equal to the k-th power of 2, the averaging circuit 443 functions as a shifter that shifts the count CNT_N toward least significant bit positions by k bits and outputs the (k+1)th least significant bit and higher-order bits.
An operation performed by the semiconductor integrated circuit 41 according to the present embodiment will now be described with reference to a timing diagram of
In the monitor circuit 42_i, the counter 423 is initialized (for a period of time between t1 and t2) when the reset signal RE is 1. Subsequently, the first pulse signal of the clock pulse signal EN_PULSE rises (at time t3). Next, the second pulse signal of the clock pulse signal EN_PULSE rises (at time t4). In the monitor circuit 42_i, the frequency divider 421 outputs an enable signal EN of 1 during a period T between t3 and t4, that is, during a period between the instant at which the clock pulse signal EN_PULSE rises and the instant at which the same signal EN_PULSE rises again. The ring oscillator 422 oscillates during the period T and outputs the oscillation signal ROOUT to the counter 423. The counter 423 counts the oscillations of the oscillation signal ROOUT during the period T, and stores the resulting count C4. Here, the count C4_i indicates a value T/TROSC1 that corresponds to the oscillation cycle TROSC1 of the ring oscillator 422 (at time t4).
Next, the value of the control signal MODE changes from 0 to 1 (at time t5). It means that the selected mode changes from the count mode to the shift mode. The counters 423 of the monitor circuits 42_1 to 42_N are then serially coupled to form an N-bit shift register. When the register value REG_i is m bits wide, the flip-flops that are included in the monitor circuits 42_1 to 42_N and provided for the associated bits are serially coupled to form the N-bit shift register.
At time t5 and later, the monitor circuit 42_i fetches the register value REG_i−1 output from the preceding monitor circuit 42_i−1 in synchronism with the shift pulse signal SHIFT_PULSE, and outputs the fetched register value to the monitor circuit 42_i+1 as the register value REG_i. It should be noted that the monitor circuit 42_N outputs the register value REG_N to the summing circuit 44.
The adder 441 included in the summing circuit 44 adds the output signal of the flip-flop 442 to the register value REG_N output from the monitor circuit 42_N, and outputs the resulting value to the flip-flop 442. The flip-flop 442 fetches the signal output from the adder 441 in synchronism with the shift pulse signal SHIFT_PULSE, and outputs the fetched signal as the count CNT_N. More specifically, the flip-flop 442 outputs the total count CNT_N of the monitor circuits 42_1 to 42_N after the shift pulse signal SHIFT_PULSE rises N times.
The averaging circuit 443 divides the count CNT_N by N, and outputs the resulting value as the average count C4AVE. In other words, the averaging circuit 443 divides the count CNT_N by N and outputs the resulting value CNT_N/N as a final monitor output value.
As described above, the semiconductor integrated circuit according to the present embodiment can detect an average value representing the variations in the characteristics in a chip by using the monitor circuits disposed at plural locations within the chip. Here, the semiconductor integrated circuit according to the present embodiment controls the oscillation time of the ring oscillator included in each monitor circuit by using the clock pulse signal EN_PULSE alone. Therefore, like the semiconductor integrated circuit according to the first embodiment, the semiconductor integrated circuit according to the present embodiment ensures that the ring oscillators included in the monitor circuits precisely agree in oscillation time. Consequently, the semiconductor integrated circuit according to the present embodiment can monitor the performance of the chip with high accuracy. Further, in the semiconductor integrated circuit according to the present embodiment, all the outputs of the monitor circuits need not be coupled to the summing circuit 44. In other words, the semiconductor integrated circuit according to the present embodiment is configured by merely coupling the output of each monitor circuit to a neighboring monitor circuit. This makes it possible to reduce the overall wiring length.
In the present embodiment, the summing circuit 44 divides the count CNT_N by N and outputs the resulting value CNT_N/N as the monitor output value. However, the present invention is not limited to the use of such a circuit configuration. The present invention can also be applied to a circuit configuration in which the count CNT_N is output as the monitor output value instead of the count CNT_N/N. If such an alternative circuit configuration is employed, the averaging circuit 443 is not required.
In the present embodiment, it is assumed that the control signal MODE changes the coupling relationship between the included units of the counter 423. However, the present invention is not limited to the use of such a circuit configuration. The present invention can also be applied to a circuit configuration that includes a counter 426 and a register 427 in place of the counter 423 as shown in
A semiconductor integrated circuit 51 according to a fifth embodiment of the present invention will now be described. The semiconductor integrated circuit 51 differs from the semiconductor integrated circuit 11 according to the first embodiment in that the former includes a control circuit 53 in place of the control circuit 13 and monitor circuits 52_1 to 52_N in place of the monitor circuits 12_1 to 12_N, where N is equal to the k-th power of 2 (k is 0 or a greater integer). The other circuit elements are the same as those used in the first embodiment and will not be redundantly described.
The control circuit 53 outputs the select signal SEL in addition to the reset signal RE and the clock pulse signal EN_PULSE. In the other respects, the control circuit 53 has the same circuit configuration as the control circuit 13. It should be noted that the clock pulse signal EN_PULSE output from the control circuit 53 includes two pulse signals.
The frequency divider 521 frequency-divides the clock pulse signal EN_PULSE by two, and outputs the resulting frequency-divided signal to the ring oscillators 522A, 522B as the enable signal EN.
The NAND 525A included in the ring oscillator 522A inputs an inverted version of the select signal SEL. The NAND 525B included in the ring oscillator 522B inputs the select signal SEL. Thus, either the ring oscillator 522A or the ring oscillator 522B, whichever is selected by the select signal SEL, oscillates during a period T during which the enable signal EN is 1, and outputs the oscillation signal ROOUT. The ring oscillators 522A, 522B will not be described in detail because they have the same circuit configuration as the ring oscillator 122 used in the first embodiment. The NANDs 525A, 525B correspond to the NAND 125. The delay gates 524A, 524B correspond to the delay gate 124. The number of elements (e.g., inverters) forming the delay gates 524A, 524B is limited to the minimum without affecting their delay time.
The selector 526 selects the oscillation signal ROOUT of a ring oscillator selected by the select signal SEL, and outputs the selected signal to the counter 523. The counter 523 is initialized to a count of 0 by the reset signal RE before the enable signal EN is set to 1. Subsequently, the counter 523 counts the oscillations (pulses) of the oscillation signal ROOUT and outputs the resulting count as a count C5_i.
The elements (e.g., inverters) included in the delay gates 524A, 524B differ in threshold voltage. Therefore, when the select signal SEL is 0, the counter 523 outputs a count T/TROSCA corresponding to the oscillation cycle TROSCA of the ring oscillator 522A as the count C5_i. When, on the other hand, the select signal SEL is 1, the counter 523 outputs a count T/TROSCB corresponding to the oscillation cycle TROSCB of the ring oscillator 522B as the count C5_i.
As described above, the semiconductor integrated circuit according to the present embodiment can detect an average value representing the variations in the characteristics in a chip by using the monitor circuits disposed at plural locations within the chip. Here, the semiconductor integrated circuit according to the present embodiment controls the oscillation time of the ring oscillator included in each monitor circuit by using the clock pulse signal EN_PULSE alone. Therefore, like the semiconductor integrated circuit according to the first embodiment, the semiconductor integrated circuit according to the present embodiment ensures that the ring oscillators included in the monitor circuits precisely agree in oscillation time. Consequently, the semiconductor integrated circuit according to the present embodiment can monitor the performance of the chip with high accuracy. Further, each monitor circuit includes plural ring oscillators having elements that differ in threshold value. Therefore, even when elements included in a chip differ in threshold voltage, the variations in their characteristics can be accurately detected. In this instance, the area occupied by each monitor circuit is increased merely by one ring oscillator and the selector 526. It means that the increase in the occupied area is minimized.
In the present embodiment, it is assumed that each monitor circuit includes two ring oscillators. However, the present invention is not limited to the use of such a circuit configuration. The present invention can also be applied to a circuit configuration in which each monitor circuit includes any number of ring oscillators. When such an alternative circuit configuration is employed, the number of select signals generated by the control circuit needs to be increased in accordance with the number of ring oscillators.
In the present embodiment, it is also assumed that the number of elements (e.g., inverters) forming the delay gates 524 is limited without affecting their delay time. However, the present invention is not limited to the use of such a circuit configuration. Alternatively, any appropriate number of elements (e.g., inverters) may be used to form the delay gates 524 without affecting their delay time.
The comparator circuit 651 included in the voltage control circuit 65 compares an average count C6AVE, which is output from the summing circuit 64, against the target value. When the average count C6AVE is greater than the target value, the comparator circuit 651 outputs a control signal (voltage control signal) so as to instruct the voltage supply circuit 66 to lower the supply voltage VDD. When, on the other hand, the average count C6AVE is smaller than the target value, the comparator circuit 651 outputs a control signal so as to instruct the voltage supply circuit 66 to raise the supply voltage VDD.
The voltage supply circuit 66 changes the supply voltage VDD in accordance with a control output generated from the comparator circuit 651. When the monitoring operation by the semiconductor integrated circuit 61 (an operation for detecting the variations in the characteristics of a chip) and the supply voltage VDD control operation by the voltage supply circuit 66 are repeated as described above, the output value (average count C6AVE) generated from the summing circuit 64 eventually converges to the target value.
As described above, the semiconductor integrated circuit according to the present embodiment can detect an average value representing the variations in the characteristics in a chip by using the monitor circuits disposed at plural locations within the chip. Here, the semiconductor integrated circuit according to the present embodiment controls the oscillation time of the ring oscillator included in each monitor circuit by using the clock pulse signal EN_PULSE alone. Therefore, like the semiconductor integrated circuit according to the first embodiment, the semiconductor integrated circuit according to the present embodiment ensures that the ring oscillators included in the monitor circuits precisely agree in oscillation time. Consequently, the semiconductor integrated circuit according to the present embodiment can monitor the performance of the chip with high accuracy. Further, as the semiconductor integrated circuit according to the present embodiment additionally includes the voltage control circuit 65, it can control the supply voltage VDD in accordance with the monitor output value. Thus, the semiconductor integrated circuit according to the present embodiment can accurately cause the performance of the chip to approach the target value.
In the present embodiment, it is assumed that the comparator circuit 651 compares the monitor output value against one target value. However, the present invention is not limited to the use of such a circuit configuration. The present invention can also be applied to a circuit configuration in which the register 652 stores a maximum target value (first reference value) MAX and a minimum target value (second reference value) MIN to let the comparator circuit 651 compare the monitor output value against these target values. If, in such a circuit configuration, the monitor output value is greater than the maximum target value MAX, the comparator circuit 651 outputs a control signal so as to instruct the voltage supply circuit 66 to lower the supply voltage VDD. If, on the other hand, the monitor output value is smaller than the minimum target value MIN, the comparator circuit 651 outputs a control signal so as to instruct the voltage supply circuit 66 to raise the supply voltage VDD. This ensures that the monitor output value is eventually between the maximum target value MAX and the minimum target value MIN. When the above-described alternative circuit configuration is used, the control operation concerning the supply voltage VDD comes to a stop when the monitor output value falls within a predetermined range. This makes it possible to prevent the supply voltage VDD from being varied by subtle changes in the monitor output value.
In the present embodiment, it is also assumed that the counter included in each monitor circuit is capable of counting up to an arbitrary number. Alternatively, however, a counter having a minimum required number of digits may be used as far as it can count up to the maximum target value MAX. If, in this instance, a counter overflow is detected, it is concluded that the monitor output value is greater than the maximum target value MAX. Consequently, the supply voltage can be controlled in the same manner as in the present embodiment. This also makes it possible to reduce the area occupied by the counter.
In the present embodiment, it is also assumed that the voltage control circuit 65 controls the supply voltage VDD of the semiconductor integrated circuit 100 in accordance with the monitor output value. However, the present invention is not limited to the use of such a circuit configuration. The present invention can also be applied to a circuit configuration in which the voltage control circuit 65 controls a substrate bias. When this alternative circuit configuration is used, the voltage supply circuit 66 supplies the substrate bias to the semiconductor integrated circuit 100. If, in this instance, the monitor output value is greater than the target value, the comparator circuit 651 outputs a control signal so as to instruct the voltage supply circuit 66 to deepen the substrate bias. If, on the other hand, the monitor output value is smaller than the target value, the comparator circuit 651 outputs a control signal so as to instruct the voltage supply circuit 66 to shallow the substrate bias. When the above-described alternative circuit configuration is used, the supply voltage VDD is always maintained constant. Therefore, it is not necessary to use a level shifter even when exchanging signals with another chip.
In the present embodiment, the target value is a value that should be output from the monitor circuits when the process, voltage, and temperature of the chip having the monitor circuits are under specific conditions. Alternatively, however, an arbitrary value determined in accordance with the results of design or actual chip testing may be used as the target value.
In the present embodiment, it is also assumed that the voltage control circuit 65 is included in the semiconductor integrated circuit 61. However, the present invention is not limited to the use of such a circuit configuration. The present invention can also be applied to a circuit configuration in which the voltage control circuit 65 is positioned outside the semiconductor integrated circuit 61.
The control circuit 73 differs from the control circuit 63 in that the former additionally outputs the select signal SEL to the monitor circuits 72_1 to 72_N and additionally outputs the select signal SEL and a trigger signal TRIG to the voltage control circuit 75.
When the select signal SEL is 0, the latch circuit 753A fetches the result of comparison by the comparator circuit 751 in synchronism with the trigger signal TRIG, and outputs the result of comparison to the logic circuit 754. When, on the other hand, the select signal SEL is 1, the latch circuit 753B fetches the result of comparison by the comparator circuit 751 in synchronism with the trigger signal TRIG, and outputs the result of comparison to the logic circuit 754. The logic circuit 754 then generates a control signal in accordance with the signal output from the latch circuit 753A or the latch circuit 753B, and outputs the control signal to the voltage supply circuit 76.
An operation performed by the semiconductor integrated circuit 101 according to the present embodiment will now be described with reference to a timing diagram of
In the monitor circuit 72_i, the counter 723 is initialized (for a period of time between t1 and t2) when the reset signal RE is 1. Subsequently, the first pulse signal of the clock pulse signal EN_PULSE rises (at time t3). Next, the second pulse signal of the clock pulse signal EN_PULSE rises (at time t4). In the monitor circuit 72_i, the frequency divider 721 outputs an enable signal EN of 1 during a period T between t3 and t4, that is, during a period between the instant at which the clock pulse signal EN_PULSE rises and the instant at which the same signal EN_PULSE rises again. The ring oscillator 722A oscillates during the period T and outputs the oscillation signal ROOUT to the counter 723 through the selector 726. The counter 723 counts the oscillations of the oscillation signal ROOUT during the period T, and outputs the resulting count as a count C7_i. Here, the count C7_i indicates a value T/TROSCi that corresponds to the oscillation cycle TROSCi of the ring oscillator 722A (at time t4).
The summing circuit 74 divides the sum of counts C7_1 to C7_N by N, and outputs the resulting value as an average count C7AVE. The comparator circuit 751 compares the average count C7AVE, which is a monitor output value, against the associated target value, and outputs the result of comparison. The latch circuit 753A fetches the result of comparison in synchronism with the trigger signal TRIG, and outputs the result of comparison to the logic circuit 754 (at time t5).
Subsequently, the select signal SEL switches from 0 to 1 (at time t6). After time t6, the same operation is performed as during the period of time between t1 and t5. In the monitor circuit 72_i, however, the ring oscillator 722B oscillates during the period T and outputs an oscillation signal ROOUTB. Further, the comparator circuit 751 compares the average count C7AVE, which is calculated by using the ring oscillator 722B in each monitor circuit 72_1 to 72_N, against the associated target value, and outputs the result of comparison. The latch circuit 753B fetches the result of comparison in synchronism with the trigger signal TRIG and outputs the result of comparison to the logic circuit 754 (at time t7). After the output results of the latch circuits 753A, 753B are put into final form, the logic circuit 754 outputs a control signal to the voltage supply circuit 66 in accordance with their output results (at time t7).
When, for instance, at least either of the monitor output values derived from the ring oscillators 722A, 722B is smaller than the associated target value, the voltage control circuit 75 outputs a control signal so as to instruct the voltage supply circuit 76 to raise the supply voltage. When, on the other hand, the monitor output values derived from the ring oscillators 722A, 722B are both greater than the associated target value, the voltage control circuit 75 outputs a control signal so as to instruct the voltage supply circuit 76 to lower the supply voltage. The voltage supply circuit 76 changes the supply voltage VDD in accordance with the control signal output from the voltage control circuit 75. When the monitoring operation by the semiconductor integrated circuit 71 and the supply voltage VDD control operation by the voltage supply circuit 76 are repeated as described above, the output value (average count C7AVE) generated from the summing circuit 74 eventually converges to the target value.
As described above, the semiconductor integrated circuit according to the present embodiment can detect an average value representing the variations in the characteristics in a chip by using the monitor circuits disposed at plural locations within the chip. Here, the semiconductor integrated circuit according to the present embodiment controls the oscillation time of the ring oscillator included in each monitor circuit by using the clock pulse signal EN_PULSE alone. Therefore, like the semiconductor integrated circuit according to the first embodiment, the semiconductor integrated circuit according to the present embodiment ensures that the ring oscillators included in the monitor circuits precisely agree in oscillation time. Consequently, the semiconductor integrated circuit according to the present embodiment can monitor the performance of the chip with high accuracy. Further, as the semiconductor integrated circuit according to the present embodiment additionally includes the voltage control circuit 75, it can control the supply voltage VDD in accordance with the monitor output value. Thus, the semiconductor integrated circuit according to the present embodiment can accurately cause the performance of the chip to approach the target value. In addition, even when the chip includes plural elements differing in threshold voltage, the semiconductor integrated circuit according to the present embodiment makes it possible to control the supply voltage in accordance with their variations.
In the present embodiment, it is assumed that the number of elements (e.g., inverters) forming the delay gate included in the ring oscillator is limited without affecting the delay time. However, the present invention is not limited to the use of such a circuit configuration. Further, the number of gates may be determined in such a manner that the ring oscillators 722A, 722B have the same oscillation cycle. Such an alternative circuit configuration eliminates the necessity of preparing a target value for each ring oscillator. Therefore, the use of only one target value will be adequate for subjecting the monitor output value derived from each ring oscillator to comparison.
In the present embodiment, it is also assumed that the voltage control circuit 75 is included in the semiconductor integrated circuit 71. However, the present invention is not limited to the use of such a circuit configuration. The present invention can also be applied to a circuit configuration in which the voltage control circuit 75 is positioned outside the semiconductor integrated circuit 71.
The difference between the present invention and the related art disclosed in Japanese Unexamined Patent Publication No. 2002-100967 will now be described. The related art disclosed in Japanese Unexamined Patent Publication No. 2002-100967 has a circuit configuration for providing voltage control to ensure that the “interval between two pulse signals” agrees with the “delay time within a monitor circuit.” Meanwhile, the present invention has a circuit configuration that divides the “interval between two pulse signals (e.g., time T)” by the “delay time within a monitor circuit (e.g., TROSC)” and outputs the resulting value as a monitor output value. Both of these two circuit configurations essentially compare the “interval between two pulse signals” with the “delay time within a monitor circuit.” The “delay time within a monitor circuit” is the delay time that is determined by the characteristics of a reference delay element shown at 332 and 335 in FIG. 16 in the Japanese Unexamined Patent Publication No. 2002-100967. It corresponds to the delay time that is determined by the characteristics of the ring oscillator included in a monitor circuit used in an embodiment of the present invention.
In the semiconductor integrated circuit disclosed in Japanese Unexamined Patent Publication No. 2002-100967, a pulse generator circuit 32 (see FIG. 15 in the Japanese Unexamined Patent Publication No. 2002-100967) generates a pulse signal S32 and outputs the pulse signal to a monitor circuit 33 (see FIG. 15 in the Japanese Unexamined Patent Publication No. 2002-100967) and a delay detector circuit 34 (see FIG. 15 in the Japanese Unexamined Patent Publication No. 2002-100967). More specifically, the pulse generator circuit 32 outputs a pulse signal for starting the measurement of “monitor circuit internal delay time” to the monitor circuit 33, and outputs a pulse signal for terminating the measurement of “monitor circuit internal delay time” to the delay detector circuit 34. Thus, these pulse signals flow in different signal paths. The “monitor circuit internal delay time” is then detected as the time lag between the pulse signal S32 input into the monitor circuit 33 and the pulse signal S33 input into the delay detector circuit 34. In this instance, delay elements (1) and (2) below are added as the “monitor circuit internal delay time.”
(1) Wiring delay caused by a long layout distance between the monitor circuit and the delay detector circuit
(2) Delay caused by a signal input/output process in the monitor circuit (e.g., delay caused by buffering and a time lag between clock input into a counter and counter output finalization)
Meanwhile, in the semiconductor integrated circuit according to an embodiment of the present invention, a monitor circuit includes a frequency divider (see, for instance,
While the present invention has been described in terms of preferred embodiments, it should be understood that the present invention is not limited to those preferred embodiments. Persons of skill in the art will appreciate that variations may be made without departure from the scope and spirit of the present invention. In the embodiments described above, it is assumed that a monitor circuit includes a ring oscillator. However, the present invention is not limited to the use of such a circuit configuration. The present invention can also be applied to a circuit configuration in which an oscillator circuit other than a ring oscillator is used.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-021471 | Feb 2010 | JP | national |
