Reference signal correction circuit

• US 10,557,894 B2
• Filed: 08/07/2017
• Issued: 02/11/2020
• Est. Priority Date: 08/07/2017
• Status: Active Grant

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Linear Technology Holding, LLC (Analog Devices, Inc.)
• Inventors: Lazarov, Kalin V., Chiacchia, Robert C.
• Primary Examiner(s): O Neill, Patrick
• Application Number:
  US15/671,080
• Publication Number:
  US 20190041471A1
• Time in Patent Office: 918 Days
• CPC Class Codes: G01R 19/2503 for measuring voltage only, e.g. digital volt meters (DVM's) G01R19/2506 - G01R19/257 take precedence
• CPC Class Codes: G01R 19/32 Compensating for temperature change
• CPC Class Codes: G01R 33/0029 Treating the measured signals, e.g. removing offset or noise
• CPC Class Codes: G01R 33/0082 Compensation, e.g. compensating for temperature changes
• CPC Class Codes: G01R 35/007 Standards or reference devices, e.g. voltage or resistance standards, "golden references"
• CPC Class Codes: G05F 1/468 characterised by reference voltage circuitry, e.g. soft start, remote shutdown
• CPC Class Codes: G05F 3/02 Regulating voltage or current
• 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: H01L 23/562 Protection against mechanical damage H01L23/02, H01L23/28 take precedence

Abstract

In a system and method for correcting a stress-impaired signal in a circuit, a calibration circuit produces a first calibrated voltage based on a base-emitter voltage of one or more pnp transistors, a second calibrated voltage based on a base-emitter voltage of one or more npn transistors, and a voltage proportional to absolute temperature. A set of reference values are generated based on these voltages. A gain correction factor is calculated based on a function of the set of reference values and a set of temperature-dependent values, and the stress-impaired signal is corrected based on the gain correction factor.

Claims

1. A method, comprising:

receiving a first calibrated voltage based on a base-emitter voltage of one or more pnp transistors, a second calibrated voltage based on a base-emitter voltage of one or more npn transistors, and a reference voltage;

determining a set of reference values based on the first calibrated voltage, the second calibrated voltage, and the reference voltage;

calculating a gain correction factor based on a function of the set of reference values and a set of temperature-dependent values;

receiving an output signal based on the reference voltage; and

adjusting the output signal based on the gain correction factor.

2. The method of claim 1, further comprising:

calculating a temperature based on an initial gain correction value and a first reference value of the set of reference values;

calculating the set of temperature-dependent values based on the calculated temperature; and

repeating the calculation of the temperature, the set of temperature-dependent values, and the gain correction factor until the temperature and the gain correction factor converge to respective values, wherein each temperature calculation is based on a last-calculated gain correction factor.

3. The method of claim 2, further comprising:

determining the set of temperature-dependent values based on indexing a lookup table by the calculated temperature;

wherein calculating the gain correction factor comprises multiplying each temperature-dependent value in the set of temperature-dependent values by a respective reference value of the set of reference values, summing each result, and determining a reciprocal of the sum.

4. The method of claim 1, further comprising:

receiving a first voltage that is proportional to absolute temperature based on a base-emitter voltage of one of the pnp transistors,

wherein a first reference value of the set of reference values is determined based on the first calibrated voltage and the reference voltage,

wherein a second reference value of the set of reference values is determined based on the second calibrated voltage and the reference voltage,

wherein a third reference value of the set of reference values is determined based on the first voltage and the reference voltage.

5. The method of claim 4, wherein calculating the gain correction factor comprises:

determining the gain correction factor from one or more polynomial equations based on the set of reference values the set of temperature-dependent values, the first calibrated voltage, the second calibrated voltage, the first voltage, and the reference voltage.

6. The method of claim 4, wherein the first calibrated voltage corresponds to a sum of the base-emitter voltage of the one or more pnp transistors and the first voltage.

7. The method of claim 6, wherein the first calibrated voltage, the second calibrated voltage, and the first voltage are generated by a reference circuit, the reference circuit configured to:

operate first and second pnp transistors in a matched pair configuration based on a first base current through a first base of the first pnp transistor and a second base current through a second base of the second pnp transistor, the one or more pnp transistors comprising the first and second pnp transistors; and

generate an initial proportional-to-absolute-temperature (PTAT) voltage at a first node of a voltage divider, connected at the first base of the first pnp transistor, based on removing a current based on the first base current from the voltage divider,

wherein the first voltage is based on a function of the initial PTAT voltage.

8. The method of claim 7, wherein the removed current is based on a difference between a first voltage potential at the first base of the first pap transistor and a second voltage potential based on a resistor connected to a second base of the second pnp transistor.

9. The method of claim 7, wherein a multiplexer provides, to an analog-to-digital converter, an analog signal selected from the first calibrated voltage, the second calibrated voltage, the first voltage, and one or more analog input signals,

wherein the analog-to-digital converter generates each respective reference value of the set of reference values based on the reference voltage and a selected one of the first calibrated voltage, the second calibrated voltage, and the first voltage, and generates the output signal based on the reference voltage and the analog input signal, and

wherein a processor receives the set of reference values and the output signal from the analog-to-digital converter, calculates the gain correction factor, and adjusts the output signal based on the gain correction factor.

10. The method of claim 1, wherein the reference voltage is a stress-impaired reference voltage.

11. A circuit, comprising:

means for receiving a first calibrated voltage based on a base-emitter voltage of one or more pnp transistors, a second calibrated voltage based on a base-emitter voltage of one or more npn transistors, and a reference voltage;

means for determining a set of reference values based on the first calibrated voltage, the second calibrated voltage, and the reference voltage;

means for calculating a gain correction factor based on a function of the set of reference values and a set of temperature-dependent values;

means for receiving an output signal based on the reference voltage; and

means for correcting the output signal based on the gain correction factor.

12. The circuit of claim 11, wherein the reference voltage is a stress-impaired reference voltage.

13. A system for calibrating an output signal, comprising:

a calibration circuit providing a first calibrated pnp voltage based on a base-emitter voltage of one or more pnp transistors and a second calibrated npn voltage based on a base-emitter voltage of one or more npn transistors;

a multiplexer connected to the calibration circuit and a sense terminal, and configured to provide an analog signal selected from a sense signal at the sense terminal, the first calibrated pnp voltage, and the second calibrated npn voltage; and

an analog-to-digital converter configured to generate a digital output signal based on the analog signal selected by the multiplexer and a reference voltage;

a processor, the processor configured to;

control the multiplexer to sample the first calibrated pnp voltage, the second calibrated npn voltage, and the sense signal for the analog-to-digital converter;

receive a set of reference values from the analog-to-digital converter based on the reference voltage and a sampling of the first calibrated pnp voltage and the second calibrated npn voltage by the multiplexer;

calculate a gain correction factor based on a set of reference values and a set of temperature-dependent values;

adjust the digital output signal based on the gain correction factor to correct for errors introduced by the reference voltage.

14. The system of claim 13, wherein the processor is further configured to:

calculate a temperature based on an initial gain correction value and a first reference value of the set of reference values;

calculate the set of temperature-dependent values based on the calculated temperature; and

repeat calculations of the temperature, the set of temperature-dependent values, and the gain correction factor until the temperature and the gain correction factor converge to respective values, wherein each temperature calculation is based on a last-calculated gain correction factor.

15. The system of claim 14, wherein the processor is further configured to:

determine the set of temperature-dependent values based on indexing a lookup table by the calculated temperature;

wherein calculating the gain correction factor comprises multiplying each temperature-dependent value in the set of temperature-dependent values by a respective reference value of the set of reference values, summing each result, and determining a reciprocal of the sum.

16. The system of claim 14, wherein the processor is further configured to:

provide an output temperature value based on a convergence of the repeated calculations of the temperature.

17. The system of claim 13, wherein the calibration circuit further provides a first voltage that is proportional to absolute temperature based on the base-emitter voltage of one of the pnp transistors,

wherein a first reference value of the set of reference values is determined based on the first calibrated pnp voltage and the reference voltage,

wherein a second reference value of the set of reference values is determined based on the second calibrated npn voltage and the stress-impaired reference voltage, and

wherein a third reference value of the set of reference values is determined based on the first voltage and the reference voltage.

18. The system of claim 17, wherein the gain correction factor is determined from one or more polynomial equations based on the set of reference values the set of temperature-dependent values, the first calibrated pnp voltage, the second calibrated npn voltage, the first voltage, and the reference voltage.

19. The system of claim 18, wherein the first calibrated pnp voltage corresponds to a sum of the base-emitter voltage of the one or more pnp transistors and the first voltage.

20. The system of claim 19, wherein the calibration circuit is configured to:

operate first and second pnp transistors in a matched pair configuration based on a first base current through a first base of the first pnp transistor and a second base current through a second base of the second pnp transistor, the one or more pnp transistors comprising the first and second pnp transistors; and

generate an initial proportional-to-absolute-temperature voltage (PTAT) at a first node of a voltage divider, connected at the first base of the first pnp transistor, based on removing a current based on the first base current from the voltage divider,

wherein the first voltage is based on a function of the initial PTAT voltage.

21. The system of claim 20, wherein the removed current is based on a difference between a first voltage potential at the first base of the first pnp transistor and a second voltage potential based on a resistor connected to a second base of the second pnp transistor.

22. The system of claim 20, wherein the multiplexer provides an analog signal selected from a sense signal at the sense terminal, the first calibrated pnp voltage, the second calibrated npn voltage, and the first voltage,

wherein the analog-to-digital converter generates each respective reference value of the set of reference values based on the reference voltage and a selected one of the first calibrated pnp voltage, the second calibrated npn voltage, and the first voltage.

23. The system of claim 13, wherein the reference voltage is a stress-impaired reference voltage.