# Patent

## Title
Semiconductor device with a negative voltage regulator

## Abstract

A semiconductor device includes a negative voltage regulator capable of regulating a negative input voltage and outputting a negative output voltage. The negative voltage regulator has a driver for adjusting the negative output voltage, a first operational amplifier for outputting a driving voltage for controlling a current on a first transistor included in the driver according to a feedback voltage and a reference voltage, a second operational amplifier for outputting a driving voltage for controlling a current of a second transistor, a current source circuit having two triple-well NMOS transistors for providing the driver a current, and a voltage potential divider for generating the feedback voltage by dividing potentials of a voltage source and the negative output voltage and outputting the feedback voltage to the first operational amplifier and the second operational amplifier for adjusting the currents of the first and second transistors thereby regulating the negative output voltage.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This is a continuation-in-part of U.S. application Ser. No. 10/709,524, which was filed on 12 May, 2004 now U.S. Pat. No. 6,888,340 and is included herein by reference.


BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device with a negative voltage regulator, and more particularly, to a semiconductor device with a negative voltage regulator utilizing triple-well NMOS transistors.
2. Description of the Prior Art
There are a lot of applications that utilize regulators for tasks of regulating voltages. Many designs and patents of regulators have been developed for improving the performance of regulator circuits. One of the examples is U.S. Pat. No. 6,600,692, “Semiconductor Device with a Voltage Regulator” to Tanzawa, which is included herein by reference.
Many applications require circuits that can boost up an input power supply DC voltage to a higher DC voltage used for specialized operations. The reason for the voltage boost up is that often only standardized power supply voltages are available for supplying power to electronic circuits. However, sometimes there are situations where a circuit needs a higher voltage than one available from the associated power supply. In addition, other circuits even require a negative voltage though only positive voltages from a power supply are available. One example of such a circuit is an electrical erasable programmable read only memory (EEPROM), typically termed in the art as “flash memory”. A flash memory may require a negative voltage to perform erase operations. However, there are few achievements in regulating negative voltages. Techniques for regulating positive voltages, such as illustrated in U.S. Pat. No. 6,600,692 are not applicable to regulating negative voltages. In general, a negative pump is often utilized to generate a negative voltage. Please refer to FIG. 1. FIG. 1 is a block diagram of a prior art negative voltage generator 100. The negative voltage generator 100 includes an oscillator 110 and a negative pump 120. The oscillator 110 outputs its output to the negative pump 120, and then a negative voltage VOUT1 is output from the negative pump 120. Please refer to FIG. 2. FIG. 2 is a block diagram of a prior art negative voltage regulator 200. The negative voltage generating circuit part includes an oscillator 210 and a negative pump 220 the same as the circuit in FIG. 1. The negative voltage regulating circuit part includes an AND gate 230, a voltage potential divider 240 and a comparator 250. Vref21 and Vref22 are two reference voltages. R21 and R22 are two voltage dividing resistors. Compared to the unregulated voltage VOUT1 in FIG. 1, the voltage potential divider 240 divides the output voltage of the negative pump 220, VOUT2, and the reference voltage Vref21, and then inputs the voltage VFEBK2 generated in the voltage division into the comparator 250 to be compared with the reference voltage Vref22. The output of the comparator 250 and the output of the oscillator 210 are input to the AND gate 230, and the output of the AND gate 230 is then input to the negative pump 220. Thereby a regulation loop is formed, and the voltage VOUT2 is a regulated negative output voltage.
For circuits that require high precision, the conventional negative voltage regulator 200 illustrated in FIG. 2 is not ideal. The operation of the conventional negative voltage regulator 200 illustrated in FIG. 2 is described as below. When the potential of the voltage VOUT2 is lower than a predetermined potential, the feedback voltage VFEBK will be pulled down and the output of the comparator 250 is made digital 0 (low potential). The output of the AND gate 230 is made digital 0, hence the negative pump 220 stops charging along with the oscillator 210 and pulls up the potential of the voltage VOUT2. Contrarily, when the potential of the voltage VOUT2 is higher than the predetermined potential, the feedback voltage VFEBK will be pulled up and the output of the comparator 250 is made digital 1 (high potential). Therefore the negative pump 220 charges along with the oscillator 210 and then decreases the potential of the voltage VOUT2. The regulation as described above is limited by the comparison range of the comparator 250 and the AND gate 230, and is similar to digital feedback regulation. The potential of the regulated voltage VOUT2 still suffers significant ripple. In addition, the performance of the conventional negative voltage regulator 200 does not sufficiently meet the requirements of circuits that need to utilize negative voltages.
SUMMARY OF INVENTION
It is therefore a primary objective of the claimed invention to provide a semiconductor device with a negative voltage regulator.
Briefly described, the claimed invention discloses a semiconductor device with a negative voltage regulator. The semiconductor device includes a negative voltage regulator capable of regulating a negative input voltage and outputting a negative output voltage at a first output node. The negative voltage regulator comprises a driver for adjusting the negative output voltage, a first operational amplifier capable of outputting a driving voltage for controlling a current of a first transistor included in the driver according to a feedback voltage and a first reference voltage, a second operational amplifier capable of outputting a driving voltage for controlling a current of a second transistor included in the driver according to a second reference voltage and the feedback voltage, a current source circuit comprising two triple-well NMOS transistors and capable of providing the driver a current, and a voltage potential divider capable of generating the feedback voltage by dividing potentials of a second voltage source and the negative output voltage and outputting the feedback voltage to the first operational amplifier and the second operational amplifier for adjusting the current on the first transistor and the current on the second transistor and thereby regulating the negative output voltage.
It is an advantage of the present invention that utilization of triple-well NMOS transistors enables the biasing at a negative voltage and hence achieves negative voltage regulation. The problem of excessive ripples of the negative output voltage in the conventional negative regulator is reduced and the requirements of circuits that utilize negative voltages are met.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.



BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a block diagram of a prior art negative voltage generator.
FIG. 2 is a block diagram of a prior art negative voltage regulator.
FIG. 3 is a block diagram of the present invention semiconductor device with a negative voltage regulator.



DETAILED DESCRIPTION
Please refer to FIG. 3. FIG. 3 is a block diagram of the present invention semiconductor device 300 with a negative voltage regulator 30. The negative voltage regulator 30 includes a voltage source regulator 310, a current source circuit 320, a voltage potential divider 340, a driver 350 and two operational amplifiers 361 and 362. An unregulated negative input voltage VIN3 is input to the negative voltage regulator 30 at an input node NIN. The negative voltage regulator 30 is capable of regulating the negative input voltage VIN3 and outputting a regulated negative output voltage VOUT3 at an output node NOUT. 330 is a reference voltage generator, such as a band gap circuit, included in the present semiconductor device 300. The reference voltage generator 330 is capable of generating reference voltages utilized in the circuits included in the device 300. Reference voltages Vref31 and Vref32 are two examples of the reference voltages generated by the reference voltage generator 330.
The voltage regulator 310 is utilized to regulate a voltage source VDD. The voltage regulator 310 includes a PMOS transistor p3 and an operational amplifier 363. The source of the PMOS transistor p3 is electrically connected to the high level voltage source of the circuit, that is, VDD, and the drain of the PMOS transistor p3 is electrically connected to a node NS. As shown in FIG. 3, the two input ends of the operational amplifier 363 are separately electrically connected to the drain of the PMOS transistor p3 and a reference voltage Vref31 provided by the reference voltage generator 330, and the output end of the operational amplifier 363 is electrically connected to the gate of the PMOS transistor p3. The voltage regulator 310 is capable of providing a stable voltage source VS independent of the unstable voltage source VDD at the node Ns by fixing the voltage potential of the drain of the PMOS transistor p3 to the potential of the reference voltage Vref31. The current source circuit 320 includes two triple-well NMOS transistors n1 and n2. The current on the NMOS transistor n1 is proportional to the current on the NMOS transistor n2. The sources of the NMOS transistors n1 and n2 are electrically connected to the input node NIN. Since the NMOS transistors n1 and n2 are triple-well NMOS transistors, the voltage potentials at their drains and sources can be negative. The negative input voltage VIN3 is input to the negative voltage regulator 30 at the sources of the NMOS transistor n1 and n2. The voltage potential divider 340 is utilized to divide the negative output voltage VOUT3 and feedback the division to the present voltage regulator 30. There are many embodiments of the voltage potential divider. The voltage potential divider 340 illustrated in FIG. 3 is the simplest one. As shown in FIG. 3, the voltage potential divider 340 includes two dividing resistors R31 and R32. The two ends of the voltage potential divider 340 are electrically connected to the output node NOUT of the negative voltage regulator 30 and the node NS for dividing the voltage VS and the negative output voltage VOUT3 and feeding back the division to the present voltage regulator 30. The driver 350 includes two PMOS transistors p1 and p2. The sources of the transistors p1 and p2 are electrically connected to the node NS receiving the stable voltage source VS. The gates of the transistors p1 and p2 are electrically connected to the output ends of the operational amplifiers 361 and 362 respectively, therefore the output voltages of the operational amplifiers 361 and 362 control the current I1 that flows through the transistor p1 and the current I2 that flows through the transistor p2 respectively. Each of the two operational amplifiers 361 and 362 receives the reference voltage Vref32 generated by the reference voltage generator 330 at one input end, and electrically connects to the node NFEBK3 by the other input end receiving the feedback voltage VFEBK3.
As illustrated in FIG. 3 and the described above, the operation of the present negative voltage regulator 30 can be presented as follows. First, assume that the voltage regulator 310 and the voltage potential divider 340 are well designed and the values of the reference voltages Vref31 and Vref32 are well chosen for coordination. When the negative output voltage VOUT3 is higher than a target potential, the feedback voltage VFEBK3 increases and exceeds the reference voltage Vref32 accordingly. Thereby the output voltage of the operational amplifier 361 is at high level and the output voltage of the operational amplifier 362 is at low level, which leads to a decreasing of the current I1 and an increasing of the current I2. However, the currents on the transistor n1 and n2 are proportional. If the current I1 decreases and the current I2 increases, there must be some current flowing from the node NOUT to the transistor n1 to complement the current I1. This current will pull down the feedback voltage VFEBK3 and the negative output voltage VOUT3, that is, adjust the negative output voltage VOUT3 to the target potential level. On the contrary, if the negative output voltage VOUT3 is lower than the target potential, the feedback voltage VFEBK3 decreases and becomes lower than the reference voltage Vref32 accordingly. Thereby the output voltage of the operational amplifier 361 is at low level and the output voltage of the operational amplifier 362 is at high level, which leads to an increasing of the current I1 and a decreasing of the current 12. Similarly, if the current 11 increases and the current I2 decreases, there must be some part of current I1 flowing from the node NOUT to the voltage potential divider 340. This current will pull up the feedback voltage VFEBK3 and the negative output voltage VOUT3, that is, adjust the negative output voltage VOUT3 to the target potential level.
The present invention feeds back the division of the negative output voltage VOUT3 to the negative voltage regulator 30 for controlling the currents I1 and I2 through the transistors p1 and p2 included in the driver 350, and adjusts the potential of the negative output voltage VOUT3 to a target potential level by the variation of the currents I1 and I2. One of the characteristics of the present invention is the utilization of the two triple-well NMOS transistors. As it is known, it is better to bias the source and the base of a transistor at the same voltage potential. The triple-well NMOS transistors utilized in the present invention enables the sources and the drains of the transistors n1 and n2 to be connected to negative voltages. Therefore the sources of the transistors n1 and n2 can be the input node of the present invention negative voltage regulator, and the drain of the transistor n1 can be the output node of the present invention negative voltage regulator. Consequently the negative voltage regulation is implemented.
The circuit illustrated in FIG. 3 is one of the embodiments of the present semiconductor device with a negative voltage regulator. In implementation, the divider 340 may connect to the output node NOUT and a reference voltage Vref33 other than VS, and the elements comprised in the divider 340 and the structure of the divider 340 may be different with suitable design. The voltage regulator 310 may be omitted or be replaced by another band gap circuit. The structure of the driver 350 shown in FIG. 3 is the simplest example. Other circuits with different structures but the same function may replace the driver 350 in the present invention.
In summary, the present invention takes advantage of the property of the triple-well NMOS transistors and provides a precise and effective negative voltage regulator. The output regulated negative voltage of the present invention is stable and thereby improves the performance of the circuits that need to utilize negative voltage. It has been shown by experiment that, if the negative input voltage is −7 V with noise of 200 mV, the negative output voltage regulated by the present negative voltage regulator will be −7V with noise of less than 50 mV. In contrast to the conventional negative voltage regulator, the claimed negative voltage regulator provides negative voltage regulation with high performance and supports the operation of flash memory cards.
Please refer to FIG. 3 again. In addition to the negative voltage regulator 30 and the reference voltage generator 330, the semiconductor device 300 further comprises the negative pump 120, a clock generator 12 installed for outputting an oscillating signal OSC, the oscillator 110, and a voltage detector 14. After receiving an enable clock CLKEN generated by the voltage detector 14, the clock generator 12 generates a clock signal CLK based on the oscillating signal OSC. The negative pump 120 negatively charge-pumping the negative input voltage VIN3 according to received clock signals CLKS. The voltage detector 14 outputs the enable clock CLKEN according to the voltage level of the negative input voltage VIN3.
The voltage detector 14 comprises a comparator 16, and a plurality of serially connected pMOS transistors ph1 to ph5. The comparator 16 comprises a positive end 18 electrically connected to a gate of the transistor ph1, a negative end 20 electrically connected to ground, and an output end 22 installed for outputting the enable clock CLKEN. The transistors ph1 and ph2 have their bases electrically connected to the stable voltage source VS, while the transistors ph3 to ph5 have their bases electrically connected to the voltage source VDD.
The operation of the voltage detector 14 is described as follows: when the negative input voltage VIN3 output from the negative pump 120 is still higher than a predetermined voltage, say −10 volts, since the gate of the transistor ph1 has a voltage level still higher than zero volts, the comparator 16 generates the enable clock CLKEN, and the clock generator 12 generates the clock signal CLK based on the oscillating signal OSC and the negative pump 120 negatively charge-pumps the negative input voltage VIN3; when the negative input voltage VIN3 is lower than the predetermined voltage, since the gate of the transistor ph1 has the voltage level lower than zero volts, the comparator 16 stops generating the enable clock CLKEN, and the clock generator 12 stops generating the clock signal CLK and the negative pump 120, without receiving any clock signals CLKs, stops negatively charge-pumping the negative input voltage VIN3. Therefore, the negative pump 120 is free of junction breakdown resulting from to low, lower than −13 volts for example, the negative input voltage VIN3.
Of the preferred embodiment, the transistors ph3 to ph5 have their bases all electrically connected to the voltage source VDD. However, since the voltage source VDD will swing from 2.5 to 3.7 volts, the transistors ph3 to ph5 can have their bases electrically connected to the stable voltage source VS, so that the voltage detector 14 can detect the negative input voltage VIN3 more accurately. Moreover, the transistors ph1 to ph5 are functioning together as a voltage potential divider, which can also be realized by two serially connected resistors, such as the dividing resistors R31 and R32 of the voltage potential divider 340.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.

## Claims

1. A semiconductor device with a negative voltage regulator comprising:
a negative voltage regulator capable of regulating a negative input voltage and outputting a negative output voltage at a first output node, the negative voltage regulator comprising:
a driver for adjusting the negative output voltage, the driver comprising a first transistor and a second transistor, a first node and a second output node, wherein the first node is electrically connected with a first voltage source and the second output node is electrically connected with the first output node of the negative voltage regulator;
a first operational amplifier comprising a first input end, a second input end and an output end electrically connected with a feedback voltage, a first reference voltage and the first transistor respectively, the first operational amplifier capable of outputting a driving voltage for controlling a current of the first transistor according to the feedback voltage and the first reference voltage;
a second operational amplifier comprising a first input end, a second input end and an output end electrically connected with a second reference voltage, the feedback voltage and the second transistor respectively, the second operational amplifier capable of outputting a driving voltage for controlling a current of the second transistor according to the second reference voltage and the feedback voltage;
a current source circuit capable of providing the driver a current, the current source circuit comprising two triple-well n-type metal-oxide semiconductor (NMOS) transistors, wherein drains of the two triple-well NMOS transistors are electrically connected with a drain of the first transistor and a drain of the second transistor separately and sources of the two triple-well NMOS transistors are electrically connected with the negative input voltage;
a voltage potential divider comprising a first end, a second end and a feedback node, wherein the first end and the second end are electrically connected with a second voltage source and the first output node respectively, and the feedback node is electrically connected with the first input end of the first operational amplifier and the second input end of the second operational amplifier, the voltage potential divider capable of generating the feedback voltage by dividing the potentials of the second voltage source and the negative output voltage and outputting the feedback voltage to the first operational amplifier and the second operational amplifier for adjusting the current of the first transistor and the current of the second transistor and thereby regulating the negative output voltage;
an oscillator;
a negative pump for negatively charge-pumping the negative input voltage, the negative pump having an input end electrically connected to an output end of the oscillator, and an output end electrically connected with the sources of the two triple-well NMOS transistors; and
a voltage detector electrically connected to the negative pump for controlling the negative pump to negatively charge-pumping the negative input voltage when the negative input voltage in higher than a predetermined voltage.

2. The semiconductor device of claim 1, wherein the voltage detector comprises:
a detection voltage potential divider comprising a third end electrically connected to a third voltage source, a fourth end for receiving the negative input voltage, and a detection feedback node, the detection voltage potential divider capable of generating a detection feedback voltage on the detection feedback node by dividing the potentials of the third voltage source and the negative input voltage; and
a comparator comprising a first input end for receiving the detection feedback voltage, a second input end electrically connected to a fourth voltage source, and an output end electrically connected to the negative pump, the comparator capable of comparing the detection feedback voltage with the fourth voltage source.

3. The semiconductor device of claim 2, wherein the third voltage source is the first voltage source.

4. The semiconductor device of claim 2, wherein the third voltage source is the second voltage source.

5. The semiconductor device of claim 2, wherein the fourth voltage source is ground.

6. The semiconductor device of claim 2, wherein the detection voltage potential divider comprises a plurality of serially connected p-type MOS transistors.

7. The semiconductor device of claim 6, wherein at least one of the p-type MOS transistors comprises a base electrically connected to the first voltage source.

8. The semiconductor device of claim 6, wherein at least one of the p-type MOS transistors comprises a base electrically connected to the second voltage source.