GB2035629A - Regulated high voltage power supply - Google Patents

Abstract

In a voltage supply wherein a voltage multiplier 12' produces an output voltage level in proportion to its driving frequency, the output voltage level is regulated by incorporating in a feedback loop round the multiplier a voltage controlled oscillator 14' to vary the driving frequency in accordance with the output voltage level of the voltage multiplier. To improve operating efficiency, a buffer 18 including current amplifiers may be disposed between the output of the voltage controlled oscillator 14' and the input of the voltage multiplier 12'. Furthermore, a level shift means I3, Q8-11 may be incorporated for disabling the voltage controlled oscillator 14' and for impressing a rail voltage level +v at the output terminal To of the voltage multiplier (12'), whenever there is no command signal at Tc. <IMAGE>

Description

SPECIFICATION Regulated high voltage power supply The present invention relates to a voltage supply of the type having a frequency responsive voltage multiplier incorporated therein.

Voltage supplies of this type are used where a D.C.

output voltage must be produced at a higher level than an input rail voltage. Such voltage supplies are found where increased drive voltage is necessary for LCD's, the write voltage of EAROM's or static RAM's, and to increase operating speed in CMOS logic or microprocessor circuitry. Operating efficiencies for such voltage supplies in the prior art are relatively high only in a narrow range of loading. Furthermore, the output voltage from such prior art supplies is poorly regulated and is highly sensitive to variations in either output loading or input rail voltage.

The voltage supply of the invention operates to substantially overcome the disadvantages encountered in the prior art. Regulation is accomplished by incorporating a voltage controlled oscillator in a feedback loop between the input and output of the voltage multiplier to vary the driving frequency thereof in accordance with the output voltage level.

Improved efficiency is accomplished by including current amplification in a buffer means which matches the input characteristics of the voltage multiplier with the output characteristics of the voltage controlled oscillator. A level shift network is incorporated in a particular embodiment to inactivate the voltage multiplier while supplying its rail voltage as the output.

Figure lisa block diagram for the voltage supply of the invention; and Figure2 is a schematic diagram wherein the Figure 1 elements are combined with other circuitry in one preferred embodiment of the invention.

As shown in the block diagram of Figure 1, the voltage supply 10 of this invention includes a voltage multiplier 12 of the type that is driven at a frequency to produce an output voltage level in proportion to the frequency. A voltage controlled oscillator (VCO) 14 is disposed in a feedback loop around the voltage multiplier 12 to vary the driving frequency thereof in accordance with the output voltage level. Because the input to the voltage multiplier 12 is driven from its own output through the VCO 14, the output level of the voltage supply 10 reaches a stabilized or regulated value. This value is relatively independent of the load, the frequency response characteristic of the voltage multiplier 12, and the voltage response characteristic of the VCO 14.Furthermore, power is conserved in that the VCO 14 only oscillates at sufficiently high frequencies to maintain the output voltage level for the load being applied.

Although many embodiments of the invention are possible, circuitry for one preferred embodiment is illustrated in Figure 2 where the voltage multiplier 12' and the VCO 14' are shown. The voltage multiplier 12' includes diodes D1, D2, D3, D4, 5, D6, D7, D5, and Dg arranged in a ladder network with capacitors C1, C2, C3, C4, C5, Ce, C7 and C8. D1-D9 are connected in series between a rail level +V and an output terminal T,, while C1-C8 are separately connected between the interconnecting nodes of D1 -D5 respectively and a pair of complementary clock input terminals (2) and m alternately.This ladder network operates to boost the voltage at term inal T, in a similar manner to the well known Cockcroft Walton voltage multiplier, as is explained in an article entitled, On-Chip High-Voltage Generation in MNOS Integrated Circuits Using an Improved Voltage Multiplier Technique, which was published in the IEEE Journal of Solid-State Circuits, Vol. SC-11, No. 3, June 1976. Therefore, current is pumped along the diode chain DDs as the coupling capacitors C1, C3, C5 and C7 are charged and discharged during alternate half cycles of the clock signal, while coupling capacitors C2, C4, C8 and C5 are discharged and charged during the same half cycles.Of course, the voltage at each node in the diode chain increases progressively up to the output voltage level at T Although the ladder network of the voltage multiplier 12' was selected for the Figure 2 embodiment of the invention, those skilled in the art will realize without further explanation that other frequency responsive voltage multiplying networks could be utilized in other embodiments of the invention.

Furthermore, a capacitor (not shown) could be connected between ground and the output of the voltage multiplier 12' where a reduction in ripple is desired.

The VCO 14' includes an odd numbered plurality of inverter stages connected in a continuous loop or ring such as It, 12, and 13. A means 16 is also included for controlling the current to one or more of the inverter stages in accordance with the voltage level applied at a terminal Tv. Because an odd number of inverter stages are connected in the continuous loop, VCO 14' produces an oscillatory signal at the output of each inverter stage 11, 12 and 13. The frequency ofthese oscillatory signals depends on the combined functional characteristics of the inverter stages, especially their input capacitance which must be charged and discharged during each frequency cycle.Once the circuitry of the inverter stages 11, 12 and 13 has been chosen, however, their functional characteristics are fixed and the frequency oftheVCO 14' is then determined by the current control means 16 as is explained in U. S. Patent No.

4,072,910.

Although many different circuits could be utilized for the current control means 16 and each of the inverter stages 11,12, and 13, the embodiment of Figure 2 is directed to a particular voltage supply application wherein a command signal at a terminal Tc selectively determines which of two positive output levels is supplied. This embodiment is particularly appropriate for supplying the bi-level voltages of one polarity that are required during the read and write periods in some memory storage applications. The command signal at terminal Tc is applied to one input of a NAND gate which is disposed as inverter stage 13.The output of the VCO 14' is taken from the output of the NAND gate which is also connected to each gate electrode in a pair of complementary MOS transistors Q1 and Q2 that are disposed in a known CMOS arrangement as inverter stage I1.The drain-source channels of Qi and Q2 are series connected with the output from inverter stage Ii being taken from between these drain-source channels and connected to the input of inverter stage 12.The other input of the NAND gate is connected to the output of inverter stage 12 which may be of any known circuit arrangement, such as the CMOS arrangement of inverter stage I1.The NAND gate of inverter stage 13 only inverts the output of inverter stage 12 when the command signal at terminal Tc is positive. Therefore, without the positive level command signal no oscillatory signals are developed in the continuous loop of the VCO 14' which is then shut down with a D.C. level appearing at its output.

The current control means 16 includes MOS transistors Q3 and Q4 of the same conductivity type as Q2 and MOS transistors OS and Q6 of the same conductivity type as Q1. 03 and OS function to supply current to the inverter stage Ii from the low and high voltage rails respectively. The magnitude of this current supply is controlled through Q4 and Q6 which are combined with Q3 and Q5 respectively as conventional current mirror amplifiers CMA-1 and CMA-2.The voltage level at terminal Tv is connected at the input of CMA-1 and therefore controls the current supplied from the high voltage rail through O. Furthermore, the drain-source channel of Q6 in CMA-1 is series connected to the drain-source channel of Q4so that the same magnitude of current flows through these channels. Consequently, the voltage level at terminal Tv also controls the current supplied from the low voltage rail through O3 and this current must be equal in magnitude to that supplied from the high voltage rail.Of course, the polarity of the output from inverter 13 controls whether inverter Ii conducts current from either the high or low voltage rail and the CMA's -1 and 2 are structured to control the magnitude of this current in inverse proportion to the voltage level at terminal Tv.

This is so because the gate to source voltage of QS and 08 increases or decreases as the voltage level at the terminal Tv is decreased or increased respectively, above the conductive threshold level of Q5 and Oe. Since the frequency of VCO 14' varies in proportion to the current supplied to the inverter stage Ii as previously mentioned, that frequency will also increase or decrease as the voltage level of terminal Tv is decreased or increased respectively, above the conductive threshold level of Q5 and O.

Furthermore, the frequency range control of the VCO 14' is very broad and its frequency can be either increased or decreased monotonically throughout this control range.

Although the voltage multiplier 12 could be driven directly by the VCO 14 in many embodiments of the invention as shown in Figure 1, a buffer means 18 is included in the Figure 2 embodiment for matching the input characteristics of the ladder network in the voltage multiplier 12' with the output characteristic of the VCO 14'. Because the output of the VCO 14' is taken from the NAND gate, at least one inverter (not shown) is included in the buffer means 18 to provide the 1800 phase relationship between the drive signals at the terminals (2) and.Also, since the output level of the voltage supply 10' is boosted within the voltage multiplier 12' by charging C1 through C8 with current applied at terminals 3 (2)and the load driven by the voltage supply 10' may necessitate that current amplification be provided within the buffer means 18. The output from the NAND gate may be connected through an odd and even number of inverting amplifiers respectively to the terminals m andWin providing a means for such current amplification.Furthermore, adequate design consideration must be given to matching the characteristics of the paths taken between terminals (2) andW within the buffer means 18, so that the rise time on one terminal and the fall time on the other terminal are essentially complementary. If complementary rise and fall times are not achieved, the oscillatory signal driving terminals (2) andmwill be skewed to cause the charging of C1, C3, C5 and C7 to be out of phase with the discharging of C2, C4, C6 and C5 and vice versa.Where current amplification is provided within the buffer means 18 as discussed above, CMOS inverters may be utilized to resolve this skew problem by fixing the ratios of the P channel widths to the N channel widths in the CMOS inverters to match the characteristics of the paths taken to terminals (2) and.

Depending on the magnitude of the high voltage rail, a means may be necessary for offsetting the voltage level at the input terminal Tv of the VCO 14' relative to the voltage level at the output terminal To of the voltage multiplier 12' to determine the regulated level of that output at terminal To. To accomplish such regulation in the Figure 2 circuitry, the gate-source voltage of Q5 and 0e must be increased from its conductive threshold level in proportion with decreases in the output voltage level. Although those skilled in the art will recognize without further explanation that this offset may be accomplished in several different ways, in the Figure 2 embodiment of the invention it is accomplished by series connecting a number of diodes DA through DN to drop the voltage level between terminals To and Tv.The drain source channel of a MOS transistor Q7 is also connected between terminal Tv and the low voltage rail while the high voltage rail is applied to the gate electrode of Q7 which then functions as a current sink.

In the memory read'write application of the Figure 2 embodiment, the high voltage rail must be supplied at terminal To of the voltage multiplier 12' when the low level of the command signal is applied to terminal Tc. This is accomplished with a level shifting meansfordisablingtheVCO 14' and for impressing the high rail voltage at terminal To in response to the command signal. The high voltage rail is applied to terminal To through the drainsource channel of a MOS transitor 08. The gate electrode of Us is connected to terminal Tc through the series connected drain-source channels of transistors Q9 and Qo of complementary conductivity type to Q8 and also connected to terminal To through the drain-source channel of a MOS transistor Qtt of the same conductivity type as 08. The gate electrodes of Qg and Qao are commonly connected and the high voltage rail is applied thereto, while the gate electrode of Q11 is connected to terminal Tc through an inverter 14.The VCO 14' is disabled through its NAND gate when the level shifting means is incorporated.

As was discussed previously, the VCO 14' is disabled when the low level of the command signal is applied to the one input ofthe NAND gate. This results in the shutting down of the voltage multiplier 12' because the VCO 14' then produces a D.C.

output. However, Qg and 010 become conductive when the low level of the command signal is applied to terminal Tc which renders Os conductive and applies the high voltage rail at terminal To. This low level command signal renders Q" non-conductive through the inverter 14.However, when the high level of the command signal is applied to terminal Tc, Q11 is rendered conductive to apply the output from the voltage multiplier 12' at the gate electrode of Q8 which then becomes non-conductive to isolate the high voltage rail from the terminal To. Qg and Qlo also become non-conductive to isolate the gate electrode of Os from terminal Tc when the high level command signal is applied.

Although this invention has been disclosed herein by describing only the preferred embodiments thereof, it should be understood by those skilled in the art that numerous changes in the details of construction and the combination or arrangement of parts could be made in the described embodiments without departing from the true scope and spirit of the invention. Therefore, the present disclosure should be construed as illustrative rather than limiting.

Claims (11)

1. A voltage supply of the type in which a voltage multiplier is driven at a frequency to produce an output voltage level in proportion to the driving frequency, wherein a voltage controlled oscillator is disposed in a feedback loop around the voltage multiplier to vary the driving frequency thereof in accordance with the output voltage level.

2. The voltage supply of claim 1 further including means for disabling said voltage controlled oscillator and for impressing a rail voltage level at the output terminal ofthe voltage multiplier in response to a command signal.

3. The voltage supply of claim 2 wherein said command signal disables said voltage controlled oscillator through a gate and applies said rail voltage level to the output terminal of the voltage multiplier through the drain-source channel of a first MOS transistor having its gate electrode connected to the output terminal of the voltage multiplier through the drain-source channel in a second MOS transistor of the same conductivity type as said first transistor and also connected to receive said signal through the series connected drain-source channels in third and fourth MOS transistors of complementary conductivity type to said first transistor, said second transistor having its gate electrode connected to receive said signal through an inverter and said third and fourth transistors having their gate electrodes commonly connected to said rail voltage level.

4. The voltage supply of claim 1 wherein said voltage controlled oscillator is connected to the voltage multiplier through buffer means for amplifying the flow of current therebetween.

5. The voltage supply of claim 1 wherein said voltage controlled oscillator includes an oddnumbered plurality of inverter stages connected in a continuous loop and means for controlling the current to one or more of said inverter stages in inverse proportion with the voltage level at the output of the voltage multiplier to thereby determine the frequency of said oscillator.

6. The voltage supply of claim 5 wherein first and second MOS transistors of complementary types are arranged as a first inverter stage with their drainsource channels series connected and wherein said current controlling means separately connects the drain-source channels of said first and second transistors to high and low rail voltage levels respectively, through respective drain-source channels in third and fourth MOS transistors of the same conductivity types as said respective first and second transistors to which they connect; said third transistor having the rail voltage side of its drainsource channel connected to one side of the drainsource channel in a fifth MOS transistor of its same conductivity type; said fourth transistor having its gate electrode connected to the gate electrode of a sixth MOS transistor of the same conductivity type; said fifth and sixth transistors having one side of their drain-source channels commonly connected to the gate electrodes of said fourth and sixth transistors; said sixth transistor having the other side of its drain-source channel connected to low rail voltage level; the output from the voltage multiplier being applied to the commonly connected gate electrodes of said third and fifth transistors and current being supplied to said first inverter stage through the drain-source channel of either said third or fourth transistors of a magnitude inversely proportional to the output level of the voltage multiplier.

7. The voltage supply of claim 6 wherein the input of a second inverter stage is connected between the drain-source channels of said first and second transistors, while a NAND gate is disposed as a third inverter stage with its output commonly connected to the gate electrodes of said first and second transistors; said NAND gate having its inputs separately connected to the output from said second inverter stage and to a command signal input for disabling said voltage controlled oscillator.

8. The voltage supply of claim 7 further including means for offsetting the gate-source voltage of said third and fifth transistors relative to the output voltage of the voltage multiplier so that as that output decreases from its ultimate value, the gatesource voltage of said third and fifth transistors increases proportionately from its conductive threshold level to thereby increase the flow of current through said first inverter stage.

9. The voltage supply of claim 8 wherein said voltage offsetting means includes diodes disposed in series between the output of the voltage multiplier and the gate electrodes of said third and fifth transistors.

10. The voltage supply of claim land further including means for offsetting the voltage level between the output of the multiplier and the input of said voltage controlled oscillator to determine the regulated level of the multiplier output.

11. A voltage supply substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawing.