Voltage regulator with power boost system

Abstract: An improved voltage regulator system is provided which includes a differential amplifier (10), an output transistor (T6) having a control electrode coupled to an output of the differential amplifier (10) and a current carrying electrode fed back to an input of the amplifier, an input control transistor (T13) having a first current carrying electrode connected to the control electrode of the output transistor (T6) and a second current carrying electrode connected to a point of fixed potential (V CC ) and means for selectively applying a control signal to a control electrode of the input control transistor (T13).

Description: This invention relates to integrated semiconductor circuits and more particularly to voltage regulator systems having a power boost circuit. Voltage regulators are used for high performance systems, such as high speed dynamic random access memory systems, which are capable of rapidly charging large capacitive loads during selected periods of time while operating at low power at other times. It is known in the art to, e.g., precharge clock drivers to increase turn-on speed and to minimize power usage during standby conditions. More specifically, in U.S. Patent 4,431,927, filed April 22, 1981, by S.E. Eaton, Jr. et al, there is disclosed a clock generator wherein signals are provided to precharge bootstrap capacitors. In U.S. Patent 4,774,691, filed November 12, 1986, by H. Hidaka, there is disclosed the use of precharge signals to reduce peak currents during the start of bit line operations in a memory. U.S. Patent 4,176,387, filed on February 27, 1978, by P.D. Harper, discloses apparatus for activating and deactivating a device to allow current to flow through a slow current decay path during one period of time and to flow through a fast decay path during another period of time. U.S. Patent 3,437,912, filed on December 30, 1966, by D. Morris, discloses a constant potential power supply wherein a trigger circuit controls a switch to selectively apply charging current to a capacitor. US-A-4649291 discloses a voltage reference circuit including a function circuit which has a plurality of active elements and performs a predetermined circuit function and which is coupled between a node and a reference terminal; a potential setting circuit, coupled between a power supply terminal and the above-mentioned node, for setting a potential at this node; and a capacitor, coupled between this node and the reference terminal, for smoothing the potential at this node. The function circuit generates a control signal and a conductance between the power supply terminal and the node is varied in response to this control signal, so that the potential setting circuit keeps the potential at this node within a predetermined range, regardless of the current consumed at the function circuit. EP-A-0248381 discloses a power voltage regulator circuit having a power terminal to which an external power voltage is supplied, an output line, and a voltage-drop circuit connected between the power terminal and the output line. The voltage drop circuit includes an N-channel MOS transistor having a drain connected to the power terminal and a source connected to the output line, a constant voltage generator for supplying a voltage, lower than the external power voltage, to a gate of the MOS transistor, and a semiconductor well whose surface area serves as a channel region of the MOS transistor. The teaching of this document forms the preamble to claim 1. Although the basic voltage regulator circuits can supply high currents or power to the load for present day performance requirements the time elapse between the demand for high power from the output terminal Vout and the time at which the basic regulator circuit can supply the required high power is too long. Today's and future integrated semiconductor circuits cannot tolerate such long delays. It is an object of this invention to provide a reliable, compatible and more stable on-chip low voltage regulator system having improved performance which rapidly charges large capacitive loads to given voltages lower than that of the external supply voltage during selected intervals of time while using minimum power during standby periods or at other intervals of time. In accordance with the teachings of this invention, an improved voltage regulator system is provided which includes a differential amplifier, an output transistor having a control electrode coupled to an output of the differential amplifier and a current carrying electrode fed back to an input of the amplifier and an input control transistor having a first current carrying electrode connected to the control electrode of the output transistor and a second current carrying electrode connected to a point of fixed potential. In a preferred embodiment of the invention, the differential amplifier includes a current mirror, the output transistor is an N-channel field effect transistor with the current carrying electrode being an output of the voltage regulator system and the input control transistor is a P-channel field effect transistor having the second current carrying electrode connected to a positive power supply voltage terminal, with an input signal to a driver circuit coupled to a control electrode of the P-channel field effect transistor, the driver circuit receiving its power supply voltage from the output of the voltage regulator system. The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of the preferred embodiments of the invention, as illustrated in the accomnanving drawings. Fig. 1 illustrates a circuit diagram of one embodiment of the voltage regulator system of the present invention, and Fig. 2 indicates voltages plotted against time which occur at various points in the system of Fig. 1 during the operation of the system. Referring to Fig. 1 of the drawings in more detail, there is illustrated an embodiment of the voltage regulator system of the present invention, preferably made in an integrated semiconductor substrate in complementary metal oxide semiconductor (CMOS) technology, which includes a differential amplifier arranged in the form of a current mirror having P-channel field effect transistors T1 and T2 and N-channel field effect transistors T3, T4 and T5. It should be noted that the CMOS circuits in Fig. 1 of the drawings have P-channel field effect transistors indicated by a rectangle with a diagonal line formed within the rectangle and with a line adjacent and parallel to one side of the rectangle indicating the gate or control electrode of the transistor, and N-channel field effect transistors indicated simply by a rectangle without the diagonal line and with a line adjacent to one side of the rectangle indicating the gate or control electrode of the transistor. In Fig. 1 of the drawing, the transistor T3 is serially connected with and interposed between transistors T1 and T5, with transistor T1 being connected to a positive voltage power supply terminal Vcc, preferably having a voltage of about 5.0 volts, and with transistor T5 being connected to a point of fixed potential, preferably ground. A control electrode of transistor T1 is connected to the common point or node A between the transistors T1 and T3 and a control electrode of each of the transistors T3 and T5 is connected to a reference voltage terminal Vref having a voltage of preferably 3.5 volts, which may be supplied from any suitable voltage source. Transistors T2 and T4 are also serially connected, with transistor T2 being connected to the power supply terminal Vcc and transistor T4 being connected to the common point between transistors T3 and T5. An N-channel field effect output transistor T6 has a gate or control electrode connected to an output of the differential amplifier 10 at the common point or node B between transistors T2 and T4, with the drain electrode of the transistor T6 connected to the power supply terminal Vcc and the source electrode of the transistor T6 connected to a gate or control electrode of the transistor T4 in a feedback arrangement. The source electrode of the output transistor T6 is also connected to an output terminal Vout having a voltage of about 3.5 volts, which acts as an on-chip low voltage power supply terminal for dense, high speed circuits designed for 3.5 volt operation and formed on the same chip with other circuits designed for 5.0 volt operation, such as the differential amplifier 10. A low voltage on-chip circuit shown in Fig. 1 of the drawing which uses the output terminal Vout as a power supply terminal is a driver circuit 12 formed as a buffer circuit having first and second inverters I1 and I2, with the inverter I1 including a P-channel field effect transistor T7 serially connected with an N-channel field effect transistor T8 and the inverter I2 including a P-channel field effect transistor T9 serially connected with an N-channel field effect transistor T10. The source electrodes of the transistors T7 and T9 are connected to the output terminal Vout and the source electrodes of the transistors T8 and T10 are connected to a point of reference potential, such as ground. An output of the first inverter I1 at node C is connected to each of the gate or control electrodes of the transistors T9 and T10 of the second inverter I2. The output of the second inverter I2 at node D is connected to a large capacitive load indicated by the capacitor C L . An input terminal Vin is connected to an input of a delay circuit 14 with the output of the delay circuit 14 being connected to each of the gate or control electrodes of the transistors T7 and T8 of the first inverter I1. Also connected to the input terminal Vin is an input of a monostable or single shot multivibrator circuit 16 which has its output connected to a buffer or inverter stage 18. The inverter stage 18 includes a P-channel field effect transistor T11 serially connected with an N-channel field effect transistor T12, with the source of the transistor T11 being connected to the power supply terminal Vcc and the source of the transistor T12 being connected to a point of reference potential, such as ground. A gate or control electrode of the transistor T11 is connected to a point of reference potential, such as ground, and a gate or control electrode of the transistor 12 is connected to the output of the monostable multivibrator circuit 16. A high power control transistor T13, indicated as a P-channel field effect transistor, has a source electrode connected to the power supply terminal Vcc and a drain electrode connected to the gate electrode of the output transistor T6, with the gate or control electrode of the transistor T13 being connected to the output of the inverter stage 18 at node E. The operation of the basic voltage regulator shown in Fig. 1 which includes the differential amplifier 10 and the output transistor T6 is well known. A reference voltage, such as 3.5 volts, from any suitable source is applied to the reference terminal Vref and the voltage at the output terminal Vout stabilizes at about 3.5 volts. If the voltage at the output terminal Vout decreases, the N-channel transistor T4 begins to turn off causing an increase in voltage at node B to turn on the N-channel transistor T6 harder, while at the same time more current is being forced through N-channel transistor T3, since transistor T5 acts as a sink transistor or current source, which lowers the voltage at node A turning on the P-channel transistor T2 harder to further turn on harder the N-channel output transistor T6 which is now capable of supplying large amounts of current to the output terminal Vout and raising the voltage at terminal Vout. When the voltage at terminal Vout is raised, the N-channel transistor T4 begins to turn on harder, which lowers the voltage at node B and begins-to turn off the N-channel output transistor T6. This process continues until the voltage at Vout stabilizes at the same or similar value as that of the reference voltage at Vref. Although this basic voltage regulator circuit can supply high currents or power to the output terminal Vout, for present day performance requirements the time elapse between the demand for high power from the output terminal Vout and the time at which this basic regulator circuit can supply the required high power is too long. Today's and future integrated semiconductor circuits cannot tolerate such long delays. Thus, in accordance with the teachings of this invention, the high power control transistor T13 has been added to the voltage regulator system to provide high power or large currents to the output terminal Vout in a much shorter period of time than can be provided by the basic voltage regulator circuit 10 and T6. For a better understanding of the operation of the voltage regulator with power boost system of the present invention, reference may be had to the pulse program illustrated in Fig. 2 of the drawing, along with the circuit diagram shown in Fig. 1. At time t0 of the pulse program shown in Fig. 2, the voltage at the reference terminal Vref is at 3.5 volts and the voltage at the output voltage Vout has stabilized at the same voltage 3.5 volts in the manner described hereinabove in connection with the operation of the basic voltage regulator 10 and T6. The voltage at node E or at the gate or control electrode of the high power control transistor T13 is high, approximately at 5.0 volts, turning off the control transistor T13 since the transistor T11 of the inverter stage 18 is on. Also, at time t0 the voltage at the input terminal Vin is low or at 0 volts and the voltage across the large capacitive load C L or at the node D is low or at 0 volts, with the voltage at node B of the differential amplifier 10 being at approximately 4.3 volts, or at a voltage of 3.5 volts plus the threshold voltage of the output transistor T6, sufficient to turn on the control transistor T6 so as to maintain the voltage at the output terminal Vout at about 3.5 volts during standby. When it is desired to charge the load C L to a high voltage, i.e., to approximately 3.5 volts, at time t1 the voltage at the terminal Vin is increased to 3.5 volts to turn on the monostable or single shot multivibrator circuit 16 which, for a given time interval, turns on the N-channel transistor T12 of the inverter stage 18 lowering the voltage at node E of the inverter stage 18 to turn on the high power control transistor T13. With the control transistor T13 turned on, the voltage at node B of the differential amplifier 10 increases rapidly to quickly turn on hard the output transistor T6, which supplies a large amount of current to the output terminal Vout and in turn to the large capacitive load C L , which is coupled to the output terminal Vout, to rapidly increase the voltage on the load C L , as indicated in Fig. 2 of the drawing by the solid line. The voltage at the monostable multivibrator circuit output then returns to its initial low state and the voltage at node E returns to approximately 5.0 volts, turning off the high power control transistor T13. With the control transistor T13 being off, the differential amplifier 10 again controls the output transistor T6. It should be noted that while the input signal or pulse at the input terminal Vin is applied to the input terminal of the monostable multivibrator circuit 16, it is also being applied to the input of the delay circuit 14. After a predetermined delay in the delay circuit 14, the high voltage is applied to the first inverter I1 where it turns on the N-channel transistor T8 to lower the voltage at node C which turns on the P-channel transistor T9 to connect the output terminal Vout to the large capacitive load C L . It should be understood that the time of delay in the delay circuit 14 should be such that the P-channel transistor T9 of the second inverter I2 turns on very shortly after the N-channel output transistor T6 is turned on hard by the P-channel control transistor T13, and that the width of the pulse produced by the monostable multivibrator circuit 16, indicated by the width of the pulse at node E, i.e., the difference in time between times t1 and t2 in the pulse program of Fig. 2, is wide enough to provide on the load C L a full charge of 3.5 volts. The voltage at the input terminal Vin should remain high for at least the duration of the time that the load capacitor C L is charged. It should be noted in Fig. 2 as indicated by the solid line that the large capacitive load C L is fully charged to 3.5 volts between times t1 and t2, which may be of a time span of no more than 5 nanoseconds, whereas the time required to fully charge the load C L to 3.5 volts by the known basic voltage regulator 10 and T6 is from time tl to time t3, which may be as long as 10 nanoseconds, as indicated by the dashed line in graph C L of Fig. 2. The basic voltage regulator circuit 10 and T6 requires more time to fully charge the load C L because more time is required to increase the voltage at node B of the differential amplifier 10, as indicated in the graph of the voltage at node B by the dashed line extending between times t1 and t3, which may be a span of 10 nanoseconds. The time for the voltage at the output terminal Vout to fully recover to the 3.5 volt level when only the basic voltage regulator circuit is used is also indicated as a dashed line between times t1 and t3 in the graph of Vout in Fig. 2 of the drawings. It should be noted that due to the very high charge demand from the very large capacitive load C L , even the voltage at the output terminal Vout in the system of the present invention decreases somewhat between times t1 and t3, but this decrease, generally no greater than 0.2 volts, is very small compared with the decrease, often equal to at least 0.8 volts for similarly large capacitive loads, experienced at the output terminal Vout of the basic voltage regulator circuit 10 and T6. After the load C L has been fully charged, the voltage at node B returns to approximately 4.3 volts, or to the voltage at the output terminal Vout plus the threshold voltage of the output transistor T6,and the voltage at the output terminal Vout remains stable at about 3.5 volts, with the voltage across the capacitive load remaining also at 3.5 volts, until the voltage state at input terminal Vin changes and subsequently the capacitive load C L is discharged to ground through the N-channel transistor T10 of the second inverter of the driver circuit 12. Although a driver circuit 12 connected to a capacitive load C L has been shown as circuitry connected to the output terminal Vout, it should be understood that any capacitive load may be coupled to the output terminal Vout which must be charged at some particular time initiated by an input signal or pulse which is applied to the circuit to be charged and to the circuit which can quickly turn on the output transistor hard. Furthermore, although a differential amplifier has been illustrated which utilizes a current mirror circuit, it should be understood that any appropriate amplifier can be used for stabilizing the voltage at the output terminal Vout during intervals when a high current is not required for charging the circuit coupled to the output terminal Vout. Likewise, it should be noted that the N-channel output transistor T6 may be replaced by some other type of transistor, e.g., a P-channel field effect transistor. When the output transistor is a P-channel transistor, the gate or control electrode of the P-channel output transistor should be connected to node A instead of to node B and the control transistor T13 should be an N-channel field effect transistor having its drain electrode connected to the gate or control electrode of the P-channel output transistor T6 and its source electrode connected to a point of fixed potential such as ground, with suitable circuitry provided to turn on the N-channel control transistor T13 when high charging currents are required by the load circuit coupled to the output terminal Vout. Accordingly, it can be seen that a voltage regulator with power boost system has been provided which anticipates the need for a large supply of charging current from an output voltage terminal having a lower voltage than that of the external power supply on the chip and supplies it quickly to the capacitive load, yet uses very little power during standby conditions.

Claims: A voltage regulator system for supplying an output voltage (V OUT ) on an output, comprising first means for receiving a power supply voltage (V CC ); second means (10) coupled to a constant voltage (V REF ), the constant voltage being of a magnitude different from that of the power supply voltage (V CC ), the second means also being coupled to the output; a load (C L ); and an output transistor (T6) having a control electrode coupled to the second means (10), a first electrode coupled to the first means and a second electrode coupled to the load, whereby the output transistor (T6) is controlled by the second means (10) to clamp the voltage of the load to the constant voltage (V REF ) during a steady-state period; characterized by third means (T13) having a control electrode, a first electrode coupled to the control electrode of the output transistor (T6) and a second electrode coupled to a point of fixed potential; fourth means (16, 18) responsive to a control signal (V IN ) for generating a turn-on pulse to the control electrode of the third means (T13), whereby the output transistor (T6) is controlled by the fourth means (16, 18) and the third means (T13) so that the load is charged by the supply voltage (V CC ) for the duration of the turn-on pulse. The system of claim 1 characterized in that the second means comprises a differential amplifier (10) coupled to the power supply voltage (V CC ) and has first and second inputs and an output (B); the first input being coupled to the constant voltage (V REF ); the output transistor (T6) has the control electrode coupled to the output (B) of said differential amplifier (10), the second electrode coupled to the second input of said differential amplifier (10); the third means (T13) comprises a control transistor (T13) having a control electrode, a first electrode coupled to the control electrode of said output transistor (T6) and a second electrode coupled to a point of fixed potential; and the fourth means (16, 18) couples to the control electrode of said control transistor (T13) for selectively turning on said control transistor (T13). The system as set forth in claim 2 characterized in that said differential amplifier (10) includes a current mirror (T1, T2, T3, T4, T5). The system as set forth in any one of the above claims characterized in that said output transistor (T6) is an N-channel field effect transistor. The system as set forth in any one of the above claims 2 to 4 characterized in that said control transistor (T13) is a P-channel field effect transistor and said second electrode is connected to power supply voltage (V CC ). The system as set forth in any one of the above claims characterized in that said fourth means (16, 18) includes a monostable multivibrator circuit (16) and an input terminal (V IN ) coupled to the control electrode of said control transistor (T13) through said monostable multivibrator circuit (16). The system as set forth in claim 6 characterized by further including a load having a capacitor (C L ) and an input coupled to said input terminal (V IN ), said load being interposed between the first current carrying electrode of said output transistor (T6) and a second point of fixed potential (GND). The system as set forth in claim 7 characterized in that said load further includes a driver circuit (12) having an input coupled to said input terminal (V IN ) and an output connected to said capacitor (C L ). The system as set forth in any one of the claims 6 to 8 characterized by further including a delay circuit (14) having an input connected to said input terminal (V IN ) and an output coupled to the input of said driver circuit (12). The system as set forth in any one of the claims 6 to 9 characterized in that said monostable multivibrator circuit (16) includes an input and an output and said means (16, 18) further includes an inverter stage (18) having an input coupled to the output of said monostable multivibrator circuit (16) and an output coupled to the control electrode of said control transistor (T13), the input of said monostable multivibrator circuit (16) being coupled to said input terminal (V IN ). The system as set forth in claim 10 characterized in that said inverter stage (18) is interposed between the first current carrying electrode of said output transistor (T6) and the point of fixed potential. The system as set forth in any one of the claims 8 to 11 characterized in that said driver circuit (12) includes first and second inverters (I1, I2), each of said inverters (I1, I2) having an input and an output, the input of said first inverter being coupled to said input terminal, the output of said first inverter being connected to the input of said second inverter and the output of said second inverter being connected to said capacitor (C L ).

Inventors: SARTWELL ALFRED L, THOMA ENDRE P, SARTWELL, ALFRED L., THOMA, ENDRE P.
Applicants: IBM, INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 1990
Main classification: G05F1
IPC codes: G11C11, G05F3, G05F1