Bandgap voltage comparator used as a low voltage detection circuit

• US 6,268,764 B1
• Filed: 02/18/2000
• Issued: 07/31/2001
• Est. Priority Date: 02/18/2000
• Status: Expired due to Term

• Current Assignee: Microchip Technology Incorporated
• Original Assignee: Microchip Technology Incorporated
• Inventors: Smit, Willem, Eagar, Layton
• Primary Examiner(s): Zweizig, Jeffrey
• Application Number:
  US09/506,999
• Time in Patent Office: 529 Days
• Field of Search: 323/313, 323/314, 323/315, 327/72, 327/77, 327/143, 327/538, 327/539, 327/543
• US Class Current: 327/539
• CPC Class Codes: G05F 3/265 using bipolar transistors only
• CPC Class Codes: G05F 3/30 Regulators using the difference between the base-emitter voltages of two bipolar transistors operating at different current densities G05F3/26 takes precedence
• CPC Class Codes: G06F 1/24 Resetting means
• CPC Class Codes: H03K 17/22 Modifications for ensuring a predetermined initial state when the supply voltage has been applied bi-stable generators H03K3/12
• CPC Class Codes: H03K 17/223 in field-effect transistor switches

Abstract

A bandgap voltage comparator requiring the summing of only two current sources is used to detect low voltage conditions for an logic on an integrated circuit that may be powered from a battery, fuel cell, solar cell and the like. Independent high and low voltage trip points may be programmed in the bandgap low voltage detection system. A power-on-reset delay may be used before asserting a voltage level ok status signal. Power may be disconnected from the bandgap voltage comparator low voltage detection system to conserve power, and power can be reapplied to quickly determine whether a desired voltage level is present.

Claims

1. A bandgap voltage comparator, comprising:

first and second transistors forming a first current mirror, wherein the second transistor is diode connected;

third and fourth transistors forming a second current mirror, wherein the third transistor is diode connected;

each of the first, second, third and fourth transistors comprising an emitter, base and collector;

a first resistor having a first and a second end, wherein the first end is connected to the base and the collector of the second transistor, and to the base of the first transistor;

the first resistor second end is connected to a first voltage node;

a second resistor having a first and a second end, wherein the first end is connected to the base and collector of the third transistor, and to the base of the fourth transistor;

the second resistor second end is connected to the first resistor first end; and

the first, second, third and fourth transistor emitters are connected to a second voltage node.

2. The bandgap voltage comparator of claim 1, wherein the first and second transistors have substantially the same emitter areas.

3. The bandgap voltage comparator of claim 1, wherein the third and fourth transistors have substantially the same emitter areas.

4. The bandgap voltage comparator of claim 1, wherein the third and fourth transistors have emitter areas from about four to forty-eight times the emitter areas of the first and second transistors.

5. The bandgap voltage comparator of claim 4, wherein the third and fourth transistor emitter areas are an integer multiple of the first and second transistor emitter areas.

6. The bandgap voltage comparator of claim 1, wherein the resistance of the first resistor is from about five to fifteen times the resistance of the second resistor.

7. The bandgap voltage comparator of claim 1, wherein the first voltage node is a common voltage node and the second voltage node is a positive voltage node referenced to the common voltage node.

8. The bandgap voltage comparator of claim 7, wherein a voltage value between the common voltage node and the positive voltage node is from about 0.6 to 5 volts.

9. The bandgap voltage comparator of claim 1, wherein the first, second, third and fourth transistors are PNP junction transistors.

10. The bandgap voltage comparator of claim 1, wherein the first, second, third and fourth transistors are NPN junction transistors.

11. The bandgap voltage comparator of claim 1, wherein the first, second, third and fourth transistors, and the first and second resistors are fabricated on an integrated circuit die.

12. The bandgap voltage comparator of claim 1, wherein a voltage trip point, V_TP, is determined by a bandgap voltage, V_tk, of the second and third transistors when the currents through the second and third transistors are equal.

13. The bandgap voltage comparator of claim 12, wherein the voltage trip point, V_TP, as a function of temperature, T_k, is determined by the equation:

14. The bandgap voltage comparator of claim 13, wherein C=3.56828, N=0.994657, and V_go=1.16056.

15. The bandgap voltage comparator of claim 14, wherein RF/RS is approximately equal to 5.384.

16. A bandgap comparator low voltage detection system, comprising:

a bandgap comparator comprising first and second transistors forming a first current mirror, and third and fourth transistors forming a second current mirror, wherein the second and third transistors are diode connected;

a resistor programming block comprising a plurality of resistors adapted to be configured into a first resistor having a resistance of RF and a second resistor having a resistance of RS, wherein the first resistor is connected to a base and collector of the second transistor and to a base of the first transistor, and the second resistor is connected to a base and collector of the third transistor and to a base of the fourth transistor; and

a bandgap comparator trip voltage detection circuit comprising a detection output and inputs for detecting a first current of the first current mirror and a second current of the second current mirror, wherein the detection output is at a first logic level when the second current is greater than the first current and is at a second logic level when the second current is less than the first current, whereby the first logic level indicates an operating voltage being above a desired voltage value and the second logic level indicates the operating voltage being below the desired voltage value.

17. The bandgap comparator low voltage detection system of claim 16, further comprising a retriggerable monostable one-shot delay circuit connected to the detection output, wherein a desired time delay is introduced when the detection output goes from the second logic level to the first logic level.

18. The bandgap comparator low voltage detection system of claim 17, further comprising an inverting buffer circuit connected between the detection output of the bandgap comparator trip voltage detection circuit and the retriggerable monostable one-shot delay circuit.

19. The bandgap comparator low voltage detection system of claim 18, further comprising a Schmitt trigger and an output enable circuit, wherein the output enable circuit disconnects voltage to the bandgap comparator low voltage detection system to conserve power thereto.

20. The bandgap comparator low voltage detection system of claim 19, wherein the bandgap comparator low voltage detection system is fabricated on an integrated circuit die and is adapted for controlling operation of digital logic circuits also fabricated on the integrated circuit die.

21. The bandgap comparator low voltage detection system of claim 20, wherein the digital logic circuits are selected from the group consisting of microcontrollers, microprocessors, digital signal processing logic, application specific integrated circuits, programmable logic arrays, and keyless and wireless entry circuits.