BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a high-to-low level shifter, and in particular relates to a high-speed high-to-low level shifter.
2. Description of the Related Art
A signal may be shifted from a higher voltage level to a lower voltage level because the receiving device may be damaged by the input signal of an overly high voltage level. For example, the input signal is a 5V signal while the receiving device can only withstand a 3.3V signal. A high-to-low level shifter is required to change the voltage level of the input signal, such as shifting it from a 5V signal to a 3.3V signal.
In addition, the required speed of integrated circuits has become faster. Thus, high-speed high-to-low level shifters are desirable to change the voltage levels of signals transmitted between high voltage devices and low voltage devices at a higher speed.
BRIEF SUMMARY OF THE INVENTION
A detailed description is given in the following embodiments with reference to the accompanying drawings.
An embodiment of a high-to-low level shifter is provided. The high-to-low level shifter comprises a high voltage unit and a low voltage unit. The high voltage unit comprises a first NMOS transistor and a second NMOS transistor. The first NMOS transistor has a gate for receiving an input signal which is at a high logic level or a low logic level. The second NMOS transistor has a gate for receiving an inverted input signal inverse to the input signal, and a drain coupled to an output node. The first and second NMOS transistors are I/O devices. The low voltage unit comprises a feed-forward circuit and a feedback circuit. The feed-forward circuit is arranged to provide an output signal to the output node in response to a voltage level of a drain of the first NMOS transistor. The feedback circuit is arranged to modify the voltage level of the drain of the first NMOS transistor according to the output signal. The feed-forward and feedback circuits are supplied by a first supply voltage lower than a voltage level of the high logic level.
Another embodiment of a high-to-low level shifter is provided. The high-to-low level shifter comprises an input node, an output node, a high voltage unit and a low voltage unit. The high voltage unit is coupled between the input node and the output node, wherein the high voltage unit has an I/O device arranged to pull down a voltage level of the output node to a signal ground when the input node is at a low logic level. The low voltage unit is coupled between the input node and the output node, wherein the low voltage unit has a core device arranged to pull up the voltage level of the output node close to a supply voltage when the input node is at a high logic level, and the supply voltage is lower than a voltage level of the high logic level.
Another embodiment of a high-to-low level shifter is provided. The high-to-low level shifter comprises a high voltage unit and a low voltage unit. The high voltage unit is arranged to receive an input signal from an input node and output a first output signal to an output node. The high voltage unit operates between a first supply voltage and a signal ground, and the input signal varies between the first supply voltage and the signal ground. The low voltage unit, coupled to the high voltage unit, is arranged to output a second output signal to the output node. The low voltage unit operates between a second supply voltage and a signal ground, and the second output signal varies between the second supply voltage and the signal ground. Only one of the first output signal and the second output signal is output to the output node and the first voltage is a higher than the second voltage.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:
FIG. 1 is a high-to-low level shifter according to an embodiment of the invention;
FIG. 2 is a high-to-low level shifter according to another embodiment of the invention;
FIG. 3 is a high-to-low level shifter according to another embodiment of the invention;
FIG. 4 is a high-to-low level shifter according to another embodiment of the invention;
FIG. 5 is a high-to-low level shifter according to another embodiment of the invention;
FIG. 6 is a high-to-low level shifter according to another embodiment of the invention; and
FIG. 7 is a high-to-low level shifter according to another embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.
FIG. 1 is a high-to-low level shifter 100 according to an embodiment of the invention. The high-to-low level shifter 100 comprises a high voltage unit 110 and a low voltage unit 120. The high voltage unit 110 comprises NMOS transistors M11 and M12 and an inverter 101. The low voltage unit 120 comprises an inverter 103 and a PMOS transistor M14. The NMOS transistors M11 and M12 and the inverter 101 are I/O (input/output) devices, and the PMOS transistor M14 and the inverter 103 are core devices. That is, the supply voltage VDDH supplied to the high voltage unit 110 is higher than the supply voltage VDDL supplied to the low voltage unit 120. For example, the supply voltage VDDH is 3.3V while the supply voltage VDDL is 1.2V or 0.9V. The NMOS transistors M11 and M12 and the inverter 101 can be operated normally between the supply voltage VDDH and the signal ground. The PMOS transistor M14 and the inverter 103 can be operated normally between the supply voltage VDDL and the signal ground.
As shown in FIG. 1, the high voltage unit 110 receives an input signal Si from an input node I1. The voltage level of input signal Si generally falls in a range from the supply voltage VDDH to the signal ground. The voltage level of output signal S0, which may be the first output signal S1 or the second output signal S2 selectively outputted to the output node O1 by the high-to-low level shifter 100, falls in a range from the supply voltage VDDL and the signal ground. When the high voltage unit 110 receives the input signal Si at a low logic level (e.g. representing “0”), of which the voltage level may be equal to the signal ground, the high voltage unit 110 outputs a first output signal S1 to the output node O1. When the high voltage unit 110 receives the input signal Si at a high logic level (e.g. representing “1”), of which the voltage level may be substantially equal to the voltage VDDH, the low voltage unit 120 outputs a second output signal S2 to the output node O1. Only one of the first output signal S1 and the second output signal S2 is outputted to the output node O1 as output signal S0. The first output signal S1 is at the signal ground, and the second output signal S2 is at a level substantially equal to the supply voltage VDDL.
When the input signal Si is at the high logic level, the NMOS transistor M11 is turned on and the NMOS transistor M12 is turned off. Then, the voltage level of a middle node N1 is pulled down to the signal ground and the PMOS transistor M14 is thus turned on. The voltage level of the output node O1 is eventually pulled up close to the supply voltage VDDL (about 1.2V or 0.9V).
When the input signal Si is at the low logic level, the NMOS transistor M11 is turned off and the NMOS transistor M12 is turned on. Then, the voltage level of the output node O1 is pulled down to the signal ground and the inverter 103 outputs a high voltage level to the middle node N1. The voltage level of the middle node N1 is close to the supply voltage VDDL (about 1.2V or 0.9V). Thus, the PMOS transistor M14 is turned off. The voltage level of the output node O1 is eventually pulled down to the signal ground.
FIG. 2 is a high-to-low level shifter 200 according to another embodiment of the invention. The high-to-low level shifter 200 comprises a high voltage unit 210 and a low voltage unit 220. The high voltage unit 210 comprises NMOS transistors M21 and M22 and an inverter 201. The low voltage unit 220 comprises PMOS transistors M23 and M24. The NMOS transistors M21 and M22 and the inverter 201 are I/O devices, and the PMOS transistors M23 and M24 are core devices. That is, the supply voltage VDDH supplied to the high voltage unit 210 is higher than the supply voltage VDDL supplied to the low voltage unit 220. For example, the supply voltage VDDH is 3.3V while the supply voltage VDDL is 1.2V or 0.9V. The NMOS transistors M21 and M22 and the inverter 201 can be operated normally between the supply voltage VDDH and the signal ground. The PMOS transistors M23 and M24 can be operated normally between the supply voltage VDDL and the signal ground.
Referring to FIG. 2, when the input signal Si is at the high logic level, the NMOS transistor M21 is turned on and the NMOS transistor M22 is turned off. Then, the voltage level of a middle node N2 is pulled down to the signal ground and the PMOS transistor M24 is thus turned on. The voltage level of the output node O2 is pulled up close to the supply voltage VDDL (about 1.2V or 0.9V). The PMOS transistor M23 is turned off since the voltage level of the output node O2 is close to the supply voltage VDDL.
When the input signal Si is at the low logic level, the NMOS transistor M21 is turned off and the NMOS transistor M22 is turned on. Then, the voltage level of the output node O2 is pulled down and the PMOS transistor M23 is turned on, such that the voltage level of the middle node N2 is pulled up close to the supply voltage VDDL (about 1.2V or 0.9V). Thus, the PMOS transistor M24 is turned off. The voltage level of the output node O2 is eventually pulled down to the signal ground since the NMOS transistor M22 is turned on and the PMOS transistor M24 is turned off.
FIG. 3 is a high-to-low level shifter 300 according to another embodiment of the invention. The high-to-low level shifter 300 comprises a high voltage unit 310 and a low voltage unit 320. The high voltage unit 310 comprises NMOS transistors M31 and M32 and an inverter 301. The low voltage unit 320 comprises a feedback circuit 303 and a PMOS transistor M34. The NMOS transistors M31 and M32 and the inverter 301 are I/O devices, the PMOS transistor M34 are core devices, and the feedback circuit 303 comprise core devices. That is, the supply voltage VDDH supplied to the high voltage unit 310 is higher than the supply voltage VDDL supplied to the low voltage unit 320. For example, the supply voltage VDDH is 3.3V and the supply voltage VDDL is 1.2V or 0.9V. The NMOS transistors M31 and M32 and the inverter 301 can be operated normally between the supply voltage VDDH and the signal ground. The PMOS transistor M34 and the feedback circuit 303 can be operated normally between the supply voltage VDDL and the signal ground.
Referring to FIG. 3, when the input signal Si is at the high logic level, the NMOS transistor M31 is turned on and the NMOS transistor M32 is turned off. Then, the voltage level of a middle node N3 is pulled down to the signal ground and the PMOS transistor M34 is thus turned on. The voltage level of an output node O3 is pulled up close to the supply voltage VDDL (about 1.2V or 0.9V) since the PMOS transistor M34 is turned on and the NMOS transistor M32 is turned off. The feedback circuit 303 is a negative feedback circuit, which is arranged to modify the voltage level of the drain of the NMOS transistor M31 according to the output signal S0, e.g. the voltage level of the output node O3.
When the input signal Si is at the low logic level, the NMOS transistor M31 is turned off and the NMOS transistor M32 is turned on. Then, the voltage level of the output node O3 is pulled down to the signal ground. The feedback circuit 303 then modifies the voltage level of the middle node N3 to be close to the supply voltage VDDL (about 1.2V or 0.9V).
FIG. 4 is a high-to-low level shifter 400 according to another embodiment of the invention. The high-to-low level shifter 400 comprises a high voltage unit 410 and a low voltage unit 420. The high voltage unit 410 comprises NMOS transistors M41 and M42 and an inverter 401. The low voltage unit 420 comprises a feedback circuit 403 and a pull-high circuit 404. The NMOS transistors M41 and M42 and the inverter 401 are I/O devices. The feedback circuit 403 and the pull-high circuit 404 comprise core devices. That is, the supply voltage VDDH supplied to the high voltage unit 410 is higher than the supply voltage VDDL supplied to the low voltage unit 420. For example, the supply voltage VDDH is 3.3V and the supply voltage VDDL is 1.2V or 0.9V. The NMOS transistors M41 and M42 and the inverter 401 can be operated normally between the supply voltage VDDH and the signal ground. The feedback circuit 403 and the pull-high circuit 404 can be operated normally between the supply voltage VDDL and the signal ground.
Referring to FIG. 4, when the input signal Si is at the high logic level, the NMOS transistor M41 is turned on and the NMOS transistor M42 is turned off. Then, the voltage level of a middle node N4 is pulled down to the signal ground. According to the voltage level of the middle node N4, e.g. the signal ground, the pull-high circuit 404 pulls up the voltage level of an output node O4 close to the supply voltage VDDL (about 1.2V or 0.9V). Moreover, the feedback circuit 403 is a negative feedback circuit, which is arranged to modify the voltage level of the middle node N4 according to the output signal S0, e.g. the voltage level of an output node O4. Therefore, by these two paths, one is provided through the pull-high circuit 404 and the other is provided through the feedback circuit 403, the voltage levels of the middle node N4 and the output node O4 respond to each other rapidly.
When the input signal Si is at the low logic level, the NMOS transistor M41 is turned off and the NMOS transistor M42 is turned on. Then, the voltage level of the output node O4 is pulled down to the signal ground since the NMOS transistor M42 is turned on. The feedback circuit 403 then modifies the voltage level of the middle node N4 to be at the supply voltage VDDL. The pull-high circuit 404 does not pull up the voltage level of the output node O4 when the voltage level of the middle node N4 is already at the supply voltage VDDL.
FIG. 5 is a high-to-low level shifter 500 according to another embodiment of the invention. The high-to-low level shifter 500 comprises a high voltage unit 510 and a low voltage unit 520. The high voltage unit 510 comprises NMOS transistors M51 and M52 and an inverter 501. The low voltage unit 520 comprises inverters 503 and 504. The NMOS transistors M51 and M52 and the inverter 501 are I/O devices. The inverters 503 and 504 are core devices. That is, the supply voltage VDDH supplied to the high voltage unit 510 is higher than the supply voltage VDDL supplied to the low voltage unit 520. For example, the supply voltage VDDH is 3.3V and the supply voltage VDDL is 1.2V or 0.9V. The NMOS transistors M51 and M52 and the inverter 501 can be operated normally between the supply voltage VDDH and the signal ground. The inverters 503 and 504 can be operated normally between the supply voltage VDDL and the signal ground.
When the input signal Si is at the high logic level, the NMOS transistor M51 is turned on and the NMOS transistor M52 is turned off. Then, the voltage level of a middle node N5 is pulled down to the signal ground. The voltage level of an output node O5 is pulled up close to the supply voltage VDDL (about 1.2V or 0.9V) by inverting the voltage level of the middle node N5 through the inverter 504. Sequentially, the inverter 503 keeps the voltage level of the middle node N5 at the signal ground according to the voltage level of the output node O5, e.g. the supply voltage VDDL (about 1.2V or 0.9V).
When the input signal Si is at the low logic level, the NMOS transistor M51 is turned off and the NMOS transistor M52 is turned on. Then, the voltage level of the output node O5 is pulled down and the inverter 503 thus makes the voltage level of the middle node N5 be close to the supply voltage VDDL (about 1.2V or 0.9V). The inverter 504 outputs a low voltage level (e.g. the signal S2) to the output node O5 according to the voltage level of the middle node N5.
FIG. 6 is a high-to-low level shifter 600 according to another embodiment of the invention. The high-to-low level shifter 600 comprises a high voltage unit 610 and a low voltage unit 620. The high voltage unit 610 comprises NMOS transistors M61 and M62 and an inverter 601. The low voltage unit 620 comprises an inverter 604 and a PMOS transistor M63. The NMOS transistors M61 and M62 and the inverter 601 are I/O devices. The PMOS transistors M63 and the inverter 604 are core devices. That is, the supply voltage VDDH supplied to the high voltage unit 610 is higher than the supply voltage VDDL supplied to the low voltage unit 620. For example, the supply voltage VDDH is 3.3V and the supply voltage VDDL is 1.2V or 0.9V. The NMOS transistors M61 and M62 and the inverter 601 can be operated normally between the supply voltage VDDH and the signal ground. The PMOS transistors M63 and the inverter 604 can be operated normally between the supply voltage VDDL and the signal ground.
Referring to FIG. 6, when the input signal Si is at the high logic level, the NMOS transistor M61 is turned on and the NMOS transistor M62 is turned off. Then, the voltage level of an input node N6 is pulled down to the signal ground. The voltage level of an output node O6 is pulled up close to the supply voltage VDDL (about 1.2V or 0.9V) by inverting the voltage level of the middle node N6 through the inverter 604. The PMOS transistor M63 is turned off since the voltage level of the output node O6 is close to the supply voltage VDDL.
When the input signal Si is at the low logic level, the NMOS transistor M61 is turned off and the NMOS transistor M62 is turned on. Then, the voltage level of the output node O6 is pulled down and the PMOS transistor M63 is thus turned on. The voltage level of a middle node N6 is pulled up close to the supply voltage VDDL (about 1.2V or 0.9V). The inverter 604 outputs a low voltage level (e.g. the signal S2) to the output node O6 according to the voltage level of the middle node N6.
FIG. 7 is a high-to-low level shifter 700 according to another embodiment of the invention. The high-to-low level shifter 700 comprises a high voltage unit 710 and a low voltage unit 720. The high voltage unit 710 comprises NMOS transistors M71 and M72 and an inverter 701. The low voltage unit 720 comprises a feedback circuit 703 and a feed-forward circuit 704. The NMOS transistors M71 and M72 and the inverter 701 are I/O devices. The feedback circuit 703 and the feed-forward circuit 704 comprise core devices. That is, the supply voltage VDDH supplied to the high voltage unit 710 is higher than the supply voltage VDDL supplied to the low voltage unit 720. For example, the supply voltage VDDH is 3.3V and the supply voltage VDDL is 1.2V or 0.9V. The NMOS transistors M71 and M72 and the inverter 701 can be operated normally between the supply voltage VDDH and the signal ground. The feedback circuit 703 and the feed-forward circuit 704 can be operated normally between the supply voltage VDDL and the signal ground.
Referring to FIG. 7, when the input signal Si is at the high logic level, the NMOS transistor M71 is turned on and the NMOS transistor M72 is turned off. Then, the voltage level of a middle node N7 is pulled down to the signal ground. The feed-forward circuit 704 is arranged to provide an output signal So to the output node O7 in response to a voltage level of a drain of the NMOS transistor M71. The feedback circuit 703 is arranged to modify the voltage level of the drain of the NMOS transistor M71 according to the output signal S0, e.g. the voltage level of the output node O7.
When the input signal Si is at the low logic level, the NMOS transistor M71 is turned off and the NMOS transistor M72 is turned on. Then, the voltage level of the output node O7 is pulled down to the signal ground. The feedback circuit 703 then modifies the voltage level of middle node N7 to be close to the supply voltage VDDL (about 1.2V or 0.9V). Sequentially, the feed-forward circuit 704 provides the output signal S0 on the output node O7 in response to the voltage level of the output node N7.
In summary, according to the above embodiments, the high voltage unit utilizes I/O devices and the low voltage unit utilizes core devices for high-speed high-to-low shifter applications. Specifically, the I/O devices which can be operated by a higher supply voltage (VDDH), and the core devices which can be operated by a lower supply voltage (VDDL). In some embodiments, the I/O devices and the core devices may have different threshold voltages (e.g. the former is greater than the later), or have different gate oxide thicknesses, or the like. Using the embodiment as illustrated in FIG. 2 as an example, since the NMOS transistor M21 or M22 is I/O device, the NMOS transistor M21 or M22 can operate at a high speed due to its high Vgs while being turned on; and, the PMOS transistor M23 and M24 can rapidly operate under the low supply voltage (VDDL) since they are implemented by core devices.
While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited to thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
Patent Application
20090058491
