METHOD AND APPARATUS FOR TIME-DIFFERENTIAL COMPARISON OF AN ANALOG SIGNAL

• US 20090160489A1
• Filed: 12/21/2007
• Published: 06/25/2009
• Est. Priority Date: 12/21/2007
• Status: Active Grant

• Current Assignee: Power Integrations Incorporated
• Original Assignee: Power Integrations Incorporated
• Inventors: Polivka, William M.
• Granted Patent: US 8,154,321 B2
• Time in Patent Office: Days
• US Class Current: 327/48
• CPC Class Codes: G01R 19/12 Measuring rate of change
• CPC Class Codes: H03K 5/24 the characteristic being amplitude
• CPC Class Codes: H03M 1/60 with intermediate conversion to frequency of pulses

Abstract

A time-differential analog comparator is disclosed. An example apparatus according to aspects of the present invention includes a source of a variable frequency signal having a frequency responsive to an analog input. A counting circuit is coupled to count cycles of the variable frequency signal. The counting circuit is coupled to count in a first direction for a first time interval and is coupled to count in a second direction opposite to the first direction for a second time interval that occurs after an end of the first time interval. An evaluation circuit is coupled to the counting circuit. The evaluation circuit is responsive to the count of the cycles of the variable frequency signal after an end of the second time interval.

Claims

1. A time-differential analog comparator, comprising:

a source of a variable frequency signal having a frequency responsive to an analog input;

a counting circuit coupled to count cycles of the variable frequency signal, wherein the counting circuit is coupled to count in a first direction for a first time interval and coupled to count in a second direction opposite to the first direction for a second time interval that occurs after an end of the first time interval;

a timing circuit coupled to the counting circuit, wherein the first time interval and the second time interval are determined by the timing circuit; and

an evaluation circuit coupled to the counting circuit and the timing circuit, wherein the evaluation circuit is responsive to a count of the cycles of the variable frequency signal after an end of the second time interval.

2. The time-differential analog comparator of claim 1 wherein the analog input is an electrical signal.

3. The time-differential analog comparator of claim 1 wherein the analog input is an intrinsic parameter of a component of a circuit.

4. The time-differential analog comparator of claim 3 wherein the component of the circuit is included in an integrated circuit.

5. The time-differential analog comparator of claim 3 wherein the intrinsic parameter is responsive to temperature.

6. The time-differential analog comparator of claim 1 wherein the timing circuit is responsive to an input that begins a sequence of timing events that includes the first time interval and the second time interval.

7. The time-differential analog comparator of claim 6 wherein the sequence of timing events includes a pause interval between the first time interval and the second time interval.

8. The time-differential analog comparator of claim 1 wherein the timing circuit is coupled to generate a signal to change an external parameter between the first time interval and the second time interval.

9. A method of performing a time-differential comparison of an analog signal, comprising:

generating a repeating signal having a frequency that varies in response to the analog signal;

counting in a first direction during a first time interval in response to cycles of the repeating signal;

counting in a second direction during a second time interval in response to the cycles of the repeating signal; and

evaluating a count of the cycles of the repeating signal after an end of the second time interval.

10. The method of claim 9 further comprising changing an external parameter between an end of the first time interval and before a beginning of the second time interval.

11. The method of claim 9 further comprising initializing the count of the cycles of the repeating signal before a beginning of the first time interval.

12. The method of claim 9 further comprising outputting a decision signal in response to the evaluation of the count of the cycles of the repeating signal after the end of the second time interval.

13. A time-differential analog comparator, comprising:

a source of a variable frequency signal having a frequency responsive to an analog input;

a counting circuit coupled to count cycles of the variable frequency signal, wherein the counting circuit is coupled to count in a first direction for a first time interval and coupled to count in a second direction opposite to the first direction for a second time interval that occurs after an end of the first time interval; and

an evaluation circuit coupled to the counting circuit, wherein the evaluation circuit is responsive to the count of the cycles of the variable frequency signal after an end of the second time interval.

14. The time-differential analog comparator of claim 13 wherein the analog input is an electrical signal.

15. The time-differential analog comparator of claim 13 wherein the analog input is an intrinsic parameter of a component of a circuit.

16. The time-differential analog comparator of claim 15 wherein the component of the circuit is included in an integrated circuit.

17. The time-differential analog comparator of claim 15 wherein the intrinsic parameter is responsive to temperature.

18. The time-differential analog comparator of claim 13 further comprising a timing circuit coupled to the counting circuit, wherein the first time interval and the second time interval are determined by the timing circuit.

19. The time-differential analog comparator of claim 18 wherein the timing circuit is responsive to an input that begins a sequence of timing events that includes the first time interval and the second time interval.

20. The time-differential analog comparator of claim 19 wherein the sequence of timing events includes a pause interval between the first time interval and the second time interval.

21. The time-differential analog comparator of claim 18 wherein the timing circuit is coupled to generate a signal to change an external parameter between the first time interval and the second time interval.