1. Field of the Invention
The present invention relates generally to voltage regulators, and more particularly to a frequency sensing voltage regulator that uses the system operating frequency to limit the amount of current delivered to a load, thereby regulating the variance of the supply voltage to the load.
2. Description of the Related Art
Voltage regulator circuits are known in which a voltage supply to a load is regulated by controlling the current supplied to the load. Typical of such prior art structures is the use of a negative feedback circuit for sensing the output voltage and/or output current which is used for comparison with a reference voltage/reference current. The difference between the output and the reference signal is used to adjust the current supplied to a load.
There are problems, however, with such voltage regulators. A considerable amount of power is drawn, and thus heat dissipated, because of the use of the negative feedback circuit. In addition, the negative feedback circuit decreases the response time to sharp current fluctuations. Furthermore, the comparator circuits and reference level generating circuits take up considerable layout area when the voltage regulator is incorporated in an integrated circuit (IC) structure.
Additional problems also occur when a voltage regulator is used to regulate the supply voltage to a synchronous device, such as a synchronous memory device, for example an SRAM. In an SRAM, an external supply voltage, Vcc, must be maintained within a predetermined level. The external supply voltage Vcc must be regulated to produce a regulated Vcc value during periods of considerable current fluctuation. For example, an SRAM load current may quickly fluctuate between microamps and milliamps during use. Such changes in the load current can cause significant variation on the regulated Vcc value, which can result in improper operation of the SRAM or possibly even damage to the SRAM.
Thus, there exists a need for a voltage regulator that is easy to implement, does not occupy significant layout area when the voltage regulator is incorporated in an integrated circuit (IC), and provides a minimal variance of the supply voltage Vcc over a wide current range.
The present invention is designed to mitigate problems associated with the prior art by providing a frequency sensing NMOS voltage regulator that is easy to implement, does not occupy significant layout area when the voltage regulator is incorporated in an integrated circuit (IC), and provides a minimal variance of the supply voltage Vcc over a wide current range. The present invention takes advantage of the fact that current tracks frequency in a linear fashion for synchronous systems.
In accordance with the present invention, a NMOS source follower transistor has a gate connected to a fixed gate voltage, a drain coupled to an external supply voltage through a PMOS switching transistor, and a source connected to a load. The gate of the PMOS transistor is controlled by a delay circuit through which the clock pulse of the system is passed. Through the use of the delay circuit and the PMOS transistor, the amount of current provided by the NMOS transistor is made a function of the cycle rate of the clock pulse, tracking the current requirements of the load. This results in a reduced variance of the regulated supply voltage Vcc over a wide current range.
These and other advantages and features of the invention will become apparent from the following detailed description of the invention which is provided in connection with the accompanying drawings.
The present invention will be described as set forth in the preferred embodiment illustrated in
The present invention provides a frequency sensing NMOS voltage regulator that is easy to implement, does not occupy significant layout area when the voltage regulator is incorporated in an integrated circuit (IC), and provides a minimal variance of the supply voltage Vcc over a wide current range.
Control circuit 14, which provides a predetermined gate voltage Vgate to transistor 12, includes a pair of PMOS transistors 30, 31, NMOS transistors 33, 34, 35, and resistors 37, 38, and 39. External supply voltage Vcc 20 and a reference voltage Vref 29 are used to supply the fixed gate voltage Vgate 16 to the gate of transistor 12 during operation of the voltage regulator 10. It should be understood that although one method of supplying a predetermined gate voltage to transistor 12, i.e., control circuit 14, has been illustrated, any method as is known in the art may be used with the present invention.
The clock pulse signal CLK PULSE 24 is connected to the reset input of each delay chain 50a-50c. The output of the last delay chain 50c is connected to a plurality of inverters 52, of which three are shown in this embodiment, connected in series.
The operation of the voltage regulator 10 of
As noted with respect to
When the input to inverters 52 is a logic high, the output 26 from delay circuit 40 will be low, keeping transistor 22 in an on state. When the input to inverters 52 is a logic low, the output 26 from the delay circuit 40 will be high, turning transistor 22 off. Each time the CLK PULSE 24 signal goes low, each of the delay chains of delay 40 will be reset, i.e., output a logic high regardless of the logic state being input to the delay chain from a previous delay chain, turning transistor 22 on. Thus, if the logic high time of the CLK PULSE 24 signal is longer than the delay time of delay circuit 40, the low ground signal will ripple through delay circuit 40 and shut off transistor 22. If the logic high time of the CLK PULSE 24 signal is less than the delay time of delay circuit 40, the logic low time of the CLK PULSE signal will reset each delay chain before the low ground signal can ripple out, pulling the output from delay circuit 40 high, thus keeping transistor 22 on. In this manner, the delay circuit 40 regulates the amount of current delivered to the load as a function of the frequency of the clock.
Clock pulse signal F3 has a shorter pulse period and thus a “high” time which is shorter than the delay time tdelay, thus not allowing the ground signal input to the first delay chain of delay circuit 40 to ripple through delay circuit 40, as each delay chain is reset each time the clock pulse signal goes low. Thus, transistor 22 remains on for the entire duration of clock pulse signal F3. Accordingly, the frequency of the clock pulse signal is used to adjust the current to the load 18 by controlling the gate voltage of transistor 22 (FIG. 1). In addition, the value of tdelay is set to correspond to the period, and thus frequency, at which the regulator begins to pulse off.
In accordance with the present invention, a frequency sensing NMOS voltage regulator is provided that is easy to implement since it only requires a simple delay circuit 40 which sets the cycle time, or frequency, at which the regulator starts pulsing off the supplied current to the load, does not occupy significant layout area when the voltage regulator is incorporated in an integrated circuit (IC), and provides a minimal variance of the regulated supply voltage Vreg over a wide current range.
It should be noted that while the invention has been described and illustrated in the environment of a memory circuit, the invention is not limited to his environment. Instead, the invention can be used in any synchronous system in which current varies linearly with clock frequency.
A typical processor system which includes a memory circuit which in turn has a voltage regulator according to the present invention is illustrated generally at 500 in
A processor system, such as a computer system, generally comprises a central processing unit (CPU) 502 that communicates with an input/output (I/O) device 504 over a bus 506. A second I/O device 508 is illustrated, but may not be necessary depending upon the system requirements. The computer system 500 also includes random access memory (RAM) 510. Power to the RAM 510 is provided by voltage regulator 10 in accordance with the present invention. Computer system 500 may also include peripheral devices such as a floppy disk drive 514 and a compact disk (CD) ROM drive 516 which also communicate with CPU 502 over the bus 506. Indeed, as shown in
In accordance with the present invention, voltage regulator 10 provides a minimal variance of the regulated supply voltage Vreg over a wide current range to a regulated device, e.g. a SRAM, or other synchronous device where load current varies linearly with clock frequency.
While a preferred embodiment of the invention has been described and illustrated above, it should be understood that this is exemplary of the invention and is not to be considered as limiting. Additions, deletions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as limited by the foregoing description but is only limited by the scope of the appended claims.
The present Application is a continuation of U.S. patent application Ser. No. 09/947,522, filed Sep. 7, 2001 (Issued as U.S. Pat. No. 6,586,916 on Jul. 1, 2003), which in turn is a continuation of U.S. patent application Ser. No. 09/692,472, filed Oct. 20, 2000 (Issued as U.S. Pat. No. 6,331,766 on Dec. 18, 2001), which in turn is a continuation of U.S. patent application Ser. No. 09/386,312, filed Aug. 31, 1999 (Issued as U.S. Pat. No. 6,175,221 on Jan. 16, 2001), the disclosures of which are herewith incorporated in their entirety.
Number | Name | Date | Kind |
---|---|---|---|
3914702 | Gehweller | Oct 1975 | A |
4267501 | Smith | May 1981 | A |
4638184 | Kimura | Jan 1987 | A |
4644184 | Miyawaki et al. | Feb 1987 | A |
4700124 | Anderson | Oct 1987 | A |
4956720 | Tomisawa | Sep 1990 | A |
5012141 | Tomisawa | Apr 1991 | A |
5130635 | Kase | Jul 1992 | A |
5568084 | McClure et al. | Oct 1996 | A |
5654663 | McClure et al. | Aug 1997 | A |
5847554 | Wilcox et al. | Dec 1998 | A |
5867048 | Chou | Feb 1999 | A |
5874830 | Baker | Feb 1999 | A |
6005819 | Shin | Dec 1999 | A |
Number | Date | Country | |
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20030197492 A1 | Oct 2003 | US |
Number | Date | Country | |
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Parent | 09947522 | Sep 2001 | US |
Child | 10443043 | US | |
Parent | 09692472 | Oct 2000 | US |
Child | 09947522 | US | |
Parent | 09386312 | Aug 1999 | US |
Child | 09692472 | US |