Patent Publication Number: US-6211727-B1

Title: Circuit and method for intelligently regulating a supply voltage

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a voltage regulator and more specifically to a circuit and method for intelligently regulating a supply voltage to a served device in which the supply voltage is regulated according to one or more performance parameters of the served device. 
     BACKGROUND OF THE INVENTION 
     The performance characteristics of a Complimentary Metallic Oxide Semiconductor (“CMOS”) device are maximized when the device operates at a certain supply voltage (the “optimal supply voltage” V OPT ). Although the value of the optimal supply voltage for a CMOS device is specified when the device is designed (the “design voltage”), variations and imperfections in the manufacturing process cause the optimal supply voltage to vary from device to device. Moreover, when the CMOS device is placed in operation, the voltage supplied to the device is rarely equal to the optimal supply voltage, or even the design voltage. In fact, the supply voltage will likely vary over time as operating conditions change. 
     As a result of these variations, CMOS devices are designed to operate within a specified voltage range, such as plus or minus five to ten percent, around the design voltage. The bottom end of the specified voltage range is limited by the threshold voltage of the CMOS device, which is the minimum voltage required to operate the device. When the voltage supplied to the CMOS device is at or near the threshold level, the device will operate, but at a much slower speed. Conversely, the top end of the specified voltage range is limited by the reliability constraints of the CMOS device. When the voltage supplied to the CMOS device is at or near its maximum operating level, the device will operate at maximum speed, but its power dissipation will be excessive. Accordingly, the goal of any voltage regulation circuit should be to maintain the supply voltage to the CMOS device at or near the optimal supply voltage for the device. Most voltage regulators, however, maintain the supply voltage at or near the design voltage; not the optimal supply voltage. 
     As discussed above, the manufacture of integrated circuit devices is not 100% repetitive. That is, the geometry of each device varies due to imperfections and variations in the manufacturing process, which in turn affects the performance characteristics of the device. Although, these devices are designed to operate within a specified voltage range, these imperfections and variations may cause some of the devices to operate too slowly, dissipate too much power, or not operate at all, at the minimum or maximum specified voltage, thus making those devices unusable and thereby decreasing the production yield. Furthermore, the production yield for a given device decreases as its complexity increases. 
     One approach taken by some designers and manufacturers to increase production yield is to provide jumpers or programmable connections on the device to alter its performance so that it operates within the specified voltage range. This method, however, only provides a “coarse” adjustment and does not assure that the device will operate at its optimal level for a given voltage, and will not track the performance of the device, especially over temperature variations. 
     These problems are multiplied as circuit designers and manufacturers continue to decrease the overall geometry of CMOS devices because the design voltages and associated operating ranges are also decreased. For example, to achieve a certain gate length, such as 0.25 microns, the supply voltage cannot exceed 3.3 volts. If the gate length is decreased to 0.18 microns, the supply voltage cannot exceed 2.0 volts. This smaller voltage range will necessarily further decrease the production yield. Moreover, systems designers employing CMOS technologies often limit the devices they use based on a range of supply voltages. As the dimensions and supply voltages of these devices decrease, the devices themselves may become unattractive to designers who are limited in device selection based on system requirements. 
     Accordingly, it is desirable to have a circuit and method for intelligently regulating a supply voltage to a served device in which the supply voltage is regulated according to one or more performance parameters of the served device. 
     SUMMARY OF THE INVENTION 
     The present invention provides a circuit and method for intelligently regulating a supply voltage to a served device according to one or more performance parameters of the served device. More specifically, the present invention comprises a sensing circuit coupled to the served device for measuring at least one performance parameter of the served device and producing a performance signal which is representative of the measured parameter(s), a discriminator circuit for comparing the performance signal to a reference signal and producing a control signal, and a voltage regulating circuit for adjusting the supply voltage to the served device in response to the control signal. 
     The present invention also provides a circuit for intelligently controlling a voltage regulating circuit, which provides a supply voltage to a served device. In this embodiment, the present invention comprises a sensing circuit coupled to the served device for measuring at least one performance parameter of the served device and producing a performance signal which is representative of the measured parameter(s), and a discriminator circuit for comparing the performance signal to a reference signal and producing a control signal for controlling the voltage regulating circuit. 
     The present invention also provides a method for regulating a supply voltage to a served device. The method comprising the steps of measuring at least one performance parameter of the served device and producing a performance signal which is representative of the measured parameter(s), comparing the performance signal to a reference signal and producing a control signal, and regulating the supply voltage to the served device in response to the control signal. 
     One advantage of the present invention is that the served device operates at or near its optimal supply voltage. As a result, the served device operates at its required speed without unnecessary power dissipation. Another advantage of the present invention is that the production yield for the served device is increased because the question of whether the served device is usable is determined by the performance of the served device and the ability of the present invention to regulate the supply voltage, rather than the performance of the served device over a specified voltage range. 
     Other objects, features and advantages of the present invention shall be apparent to those of ordinary skill in the art upon reference to the following detailed description taken in conjunction with the accompanying drawings. For example, although CMOS devices are described, the present invention can be applied to other types of semiconductor devices, as well as other electrical devices. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and further advantages of the invention may be better understood by referring to the following description in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a block diagram of an intelligent supply voltage regulator in accordance with one embodiment of the present invention; and 
     FIG. 2 is a circuit diagram of an intelligent supply voltage regulator in accordance with one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring now to the Drawings, and first to FIG. 1, a block diagram of an intelligent power supply regulator in accordance with one embodiment of the present invention is illustrated. In this embodiment, the present invention is used to adjust a supply voltage V SUP  until an adjusted supply voltage V ADJ  to a served device  12  is at or near the optimal supply voltage V OPT  of the served device  12 . Once the adjusted supply voltage V ADJ  is at or near the optimal supply voltage V OPT , the present invention continues to measure the performance parameters of the served device  12  and adjust the supply voltage V SUP  as is necessary to maintain the adjusted voltage V ADJ  at or near the optimal supply voltage V OPT  at all times despite operating and temperature variations. 
     The intelligent power supply regulator comprises a sensing circuit  14 , a discriminator circuit  16  and a voltage regulating circuit  18 . The sensing circuit  14  is coupled to the served device  12  so that at least one performance parameter of the served device  12  can be continuously measured. Since the performance parameters are continuously measured, the adjusted voltage V ADJ  can be maintained at or near the optimal supply voltage V OPT  despite operating and temperature variations. The sensing circuit  14  then produces a performance signal V PRFM  representative of the measured parameter(s). 
     A performance parameter can be any measurable property of the served device  12  that varies with a change in the adjusted supply voltage V ADJ . For example, the optimal supply voltage V OPT  for the served device  12  can be determined by measuring the transconductance of the served device  12 . 
     The method of coupling the sensing circuit  14  to the served device  12  will depend upon the parameter(s) to be measured, and the physical and functional properties of the served device  12 . For example, a sensing circuit  14  fabricated on the same integrated circuit  20  as the served device  12  can measure the physical performance properties of the integrated circuit  20  without being directly connected to the served device  12 . 
     As will be understood by those skilled in the art, the physical location of the sensing circuit  14 , the discriminator circuit  16  and the voltage regulation circuit  18  will depend upon the performance parameters that are to be measured and the operating characteristics and/or functionality of the served device  12 . For example, in most lower power integrated circuits, such as CMOS, it is either not possible or not feasible to incorporate the voltage regulation circuit  18  in the same integrated circuit  20  as the served device  12  because of the power dissipation of the voltage regulation circuit  18 . Yet, some circuit technologies may allow or make it advantageous to incorporate the voltage regulating circuit  18 , the sensing circuit  14 , the discriminator circuit  16 , and the served device  12  into a single device or circuit (not shown). So except as described herein, the present invention is not limited by the physical location of the sensing circuit  14 , the discriminator circuit  16 , or the voltage regulating circuit  18 . 
     The discriminator circuit  16  compares the performance signal V PRFM  with a reference signal V REF  and produces a control signal V CRTL . The discriminator circuit  16 , depending on the parameters measured, may contain additional circuitry to modify the performance signal V PRFM  and/or reference signal V REF  so that the two signals can be properly compared and a result determined. Moreover, additional control circuitry may be included to ensure that the control signal V CRTL  is compatible with and properly controls the voltage regulating circuit  18 . 
     The control signal V CRTL  is used to control the voltage regulating circuit  18  so that the supply voltage V SUP  is adjusted until the adjusted supply voltage V ADJ  is at or near the optimal supply voltage V OPT  of the served device  12 . Thereafter, the control signal V CRTL  is used to maintain the adjusted voltage V ADJ  at or near the optimal supply voltage V OPT  despite operating and temperature variations. 
     Still referring to FIG. 1, another embodiment of the present invention is used to control an existing or off-the-shelf voltage regulating circuit  18 , which adjusts the supply voltage V SUP  to provide the adjusted supply voltage V ADJ . This embodiment also continuously maintains the adjusted voltage V ADJ  at or near the optimal supply voltage V OPT  despite operating and temperature variations. In this case, the intelligent power supply regulator comprises a sensing circuit  14  and a discriminator circuit  16 . Otherwise, this embodiment functions in the same manner as previously described. 
     Now referring to FIG. 2, another embodiment of the present invention is illustrated. As previously described, the intelligent power supply regulator comprises a sensing circuit  14 , a discriminator circuit  16  and a voltage regulating circuit  18 . The served circuit  12 , the sensing circuit  14  and the discriminator circuit  16  are all located on the same integrated circuit  20 . 
     The sensing circuit  14  is designed to measure the transconductance of the served device  12  so that the supply voltage V SUP  can be adjusted until the adjusted supply voltage V ADJ  is at or near the optimal supply voltage V OPT  for the served device  12 . The sensing circuit  14  continuously measures the transconductance using a ring oscillator circuit, which is an odd number of series-connected invertors  22  biased by the adjusted supply voltage V ADJ  and having a feedback loop. Since the transconductance of the served device  12  is continuously measured, the adjusted voltage V ADJ  can be maintained at or near the optimal supply voltage V OPT  despite operating and temperature variations. The ring oscillator circuit (sensing circuit  14 ) produces a signal V PRFM  that oscillates at a frequency relative to the transconductance, a performance characteristic, of the served device  12 . The output of the ring oscillator (sensing circuit  14 ) is connected to the discriminator circuit  16 . 
     The discriminator circuit  16  comprises a frequency divider circuit  24  and a frequency discriminator circuit  26 . The frequency divider circuit  24  reduces the frequency generated by the ring oscillator circuit (sensing circuit  14 ) to a frequency that can be conveniently compared to a reference frequency V REF , such as an external clock. The frequency discriminator circuit  26  compares the performance signal V PRFM  with the reference signal V REF  and produces a control signal V CRTL , which is connected to the control circuit  32  of the voltage regulating circuit  18 . 
     The voltage regulating circuit  18 , which can be a switched mode voltage regulator, is connected to a battery or some other unregulated supply voltage V SUP . Typically the voltage regulating circuit  18  will contain a power transistor  28 , a passive regulation circuit  30 , which contains elements D, L and C, and a control circuit  32 . The control circuit  32 , in response to the control signal V CRTL  from the frequency discriminator  16 , adjusts the supply voltage V SUP  until the adjusted supply voltage V ADJ  is at or near the optimal supply voltage V OPT  for the served device  12  and thereafter maintains the adjusted supply voltage V ADJ  at or near the optimal supply voltage V OPT . 
     Although preferred embodiments of the invention have been described in detail, it will be understood by those skilled in the art that various modifications can be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.