Charge pump for improving memory cell low VCC performance without increasing gate oxide thickness

• US 6,215,708 B1
• Filed: 09/30/1998
• Issued: 04/10/2001
• Est. Priority Date: 09/30/1998
• Status: Expired due to Term

• Current Assignee: Integrated Device Technology Incorporated (Renesas Electronics Corporation)
• Original Assignee: Integrated Device Technology Incorporated (Renesas Electronics Corporation)
• Inventors: Lien, Chuen-Der, Wu, Chau-Chin
• Primary Examiner(s): PHAN, TRONG Q
• Application Number:
  US09/164,450
• Time in Patent Office: 923 Days
• Field of Search: 365/189.09, 365/189.11, 365/226, 365/230.06, 365/230.03, 365/189.06, 327/535, 327/536, 327/537, 327/538, 327/539, 327/540, 327/541, 371/67.1, 707/10
• US Class Current: 365/189.09
• CPC Class Codes: G11C 11/4085 Word line control circuits, e.g. word line drivers, - boosters, - pull-up, - pull-down, - precharge
• CPC Class Codes: G11C 5/145 Applications of charge pumps; Boosted voltage circuits; Clamp circuits therefor G11C5/141 takes precedence
• CPC Class Codes: G11C 8/08 Word line control circuits, e.g. drivers, boosters, pull-up circuits, pull-down circuits, precharging circuits, for word lines

Abstract

A memory circuit that operates in response to a V_CC supply voltage and a ground voltage is provided. The memory circuit includes a word line voltage generation circuit that generates a fixed word line voltage. The fixed word line voltage is selectively applied to word lines of the memory circuit. The word line voltage generation circuit generates the fixed word line voltage for all values of the V_CC supply voltage between the minimum V_CC supply voltage and the maximum V_CC supply voltage. The fixed word line voltage is referenced to the ground voltage, rather than the V_CC supply voltage. Because the ground voltage does not vary, the boosted word line voltage of the present invention can be controlled more precisely than prior art boosted word line voltages, which are referenced to the V_CC supply voltage. This improved control enables the boosted word line voltage to be fixed for the entire range of the V_CC supply voltage. This improved control also enables the boosted word line voltage to be selected to optimize the operating and design characteristics of the memory circuit.

Claims

1. A memory circuit that operates in response to a first supply voltage and a ground voltage, the first supply voltage varying between a minimum supply voltage and a maximum supply voltage during normal operating conditions of the memory circuit, the memory circuit comprising:

a memory cell array having a plurality of word lines;

a word line voltage generation circuit that generates a fixed word line voltage equal to the maximum supply voltage, provided that the first supply voltage is maintained between the minimum supply voltage and the maximum supply voltage; and

a word line access circuit for selectively transmitting the fixed word line voltage to the word lines.

2. The memory circuit of claim 1, wherein the word line voltage generation circuit comprises a reference voltage supply that generates a reference voltage.

3. The memory circuit of claim 2, wherein the reference voltage supply is referenced to the ground supply voltage.

4. The memory circuit of claim 2, wherein the reference voltage supply comprises a band gap reference regulator.

5. The memory circuit of claim 2, wherein the word line voltage generation circuit further comprises:

an oscillator that generates a clock signal;

a charge pump coupled to receive the clock signal from the oscillator, the charge pump generating the word line voltage in response to the clock signal;

a charge pump control circuit coupled to receive the word line voltage generated by the charge pump and the reference voltage generated by the reference voltage supply, the charge pump control circuit generating a control signal for enabling the charge pump when the word line voltage is less than the reference voltage.

6. The memory circuit of claim 1, wherein the word line voltage generation circuit comprises:

an oscillator that generates a clock signal;

a charge pump coupled to receive the clock signal from the oscillator, the charge pump generating the word line voltage in response to the clock signal; and

a voltage clamping circuit coupled to the charge pump, wherein the voltage clamping circuit clamps the word line voltage at the fixed word line voltage.

7. The memory circuit of claim 6, wherein the voltage clamping circuit comprises a plurality of series-connected diodes.

8. The memory circuit of claim 6, wherein the voltage clamping circuit comprises:

a V_PP voltage bus coupled to the charge pump circuit;

a first resistor coupled between the V_PP voltage bus and a first node;

a second resistor coupled between the first node and a ground voltage terminal; and

a bipolar transistor having a collector and an emitter connected across the V_PP voltage bus and the ground voltage terminal, and a base coupled to the first node.

9. The memory circuit of claim 6, wherein the voltage clamping circuit comprises:

a V_PP voltage bus coupled to the charge pump circuit;

a first resistor coupled between the V_PP voltage bus and a first node;

a second resistor coupled between the first node and a ground voltage terminal; and

a field effect transistor having a drain and a source connected across the V_PP voltage bus and the ground voltage terminal, and a gate coupled to the first node.

10. The memory circuit of claim 1, wherein the memory cell array comprises a plurality of SRAM memory cells.

11. A method of operating a memory circuit response to a first supply voltage and a ground voltage, the first supply voltage varying between a minimum supply voltage and a maximum supply voltage during normal operating conditions of the memory circuit, the method comprising the steps of:

generating a fixed word line voltage equal to the maximum supply voltage, wherein the fixed word line voltage is referenced to a ground voltage; and

applying the fixed word line voltage to selected word lines of a memory cell array.

12. The method of claim 11, wherein the step of generating the fixed word line voltage is performed by a band gap reference regulator.

13. The method of claim 11, wherein the step of generating the fixed word line voltage is performed by a voltage clamping circuit.

14. The method of claim 11, wherein the step of generating the fixed word line voltage comprises the steps of:

generating a clock signal;

generating a word line voltage with a charge pump in response to the clock signal;

generating a reference voltage equal to a predetermined fraction of the desired fixed word line voltage;

comparing the word line voltage and the reference voltage;

enabling the charge pump when the word line voltage times the pre-determined fraction is less than the reference voltage; and

disabling the charge pump when the word line voltage times the pre-determined fraction is greater than the reference voltage, whereby the word line voltage is forced to the fixed word line voltage.