Dual-mixer loss of signal detection circuit

• US 6,559,682 B1
• Filed: 05/29/2002
• Issued: 05/06/2003
• Est. Priority Date: 05/29/2002
• Status: Expired due to Term

• Current Assignee: Microsemi Storage Solutions, Inc (Microchip Technology Incorporated)
• Original Assignee: Vitesse Semiconductor Corp (Microchip Technology Incorporated)
• Inventors: Xiang, Tao, Kyles, Ian
• Primary Examiner(s): Cunningham, Terry D.
• Assistant Examiner(s): NGUYEN, LONG T
• Application Number:
  US10/159,648
• Time in Patent Office: 342 Days
• Field of Search: 327/20, 327/350, 327/352, 327/355-357, 327/353-361, 327/65, 327/346, 327/349
• US Class Current: 327/20
• CPC Class Codes: H03K 5/19 Monitoring patterns of pulse trains indicating amplitude G01R19/00; indicating frequency G01R23/00; measuring characteristics of individual pulses G01R29/02

Abstract

A loss of signal detection circuit using Gilbert mixers. A differential input signal is provided to an input Gilbert mixer. Reference signals are provided to a reference Gilbert mixer. The two Gilbert mixers pull reference lines in opposing directions such that a one line is higher than another line when the differential input signal provides valid data.

Claims

1. A loss of signal detection circuit comprising:

a plurality of Gilbert mixers;

a plurality of output lines, with each Gilbert mixer providing an output to at least two output lines;

a filter circuit coupled to the plurality of output lines, producing a filtered output; and

a comparator circuit receiving the filtered output and generating an alert signal.

2. The loss of signal detection circuit of claim 1 wherein a first Gilbert mixer receives an input signal.

3. The loss of signal detection circuit of claim 2 wherein the input signal is a differential signal.

4. The loss of signal detection circuit of claim 1 wherein a second Gilbert mixer receives an offset signal at its input.

5. The loss of signal detection circuit of claim 4 wherein the offset signal is a DC signal.

6. The loss of signal detection circuit of claim 1 wherein the filter circuit is a low pass filter circuit.

7. The loss of signal detection circuit of claim 1 wherein each Gilbert mixer comprises three differential pair of transistors.

8. The loss of signal detection circuit of claim 7 wherein two output differential pair of transistors are coupled to a plurality of the output lines;

a third differential pair of transistors coupled to each of the output differential pair of transistors; and

the third differential pair of transistors being coupled to a current source.

9. The loss of signal detection circuit of claim 1 wherein each of a plurality of the output lines are coupled to a power supply by a resistor.

12. The loss of signal detection circuit of claim 9 wherein the second Gilbert mixer biases the plurality of output lines in response to the offset signal.

13. The loss of signal detection circuit of claim 9 wherein the first Gilbert mixer alters a voltage on at least one of the plurality of output lines in response to the input signal.

14. The loss of signal detection circuit of claim 9 wherein time averaging the plurality of signals of the output lines includes passing the plurality of signals of the output lines through a low pass filter.

15. The loss of signal detection circuit of claim 9 wherein comparing voltages of the time averaged outputs comprises providing the time averaged outputs to a comparator.

16. The loss of signal detection circuit of claim 12 wherein the output lines are biased such that a first output line has a higher voltage than a second output line.

17. The loss of signal detection circuit of claim 16 wherein the first Gilbert mixer alters the voltages of the output lines such that the first output line has a lower voltage than the second output line when an input signal is present.

18. The loss of signal detection circuit of claim 17 wherein generating an alert in response to the comparison of the time averaged outputs comprises generating an alert if a time averaged version of the first output line is at a higher voltage than a time averaged version of the second output line.

10. A method of detecting a loss of signal, the method comprising:

providing an input signal to a first Gilbert mixer;

providing an offset voltage to a second Gilbert mixer;

the Gilbert mixers altering voltages on a plurality of output lines in response to the input signal and the offset voltage;

time averaging a plurality of signals of the output lines, producing time averaged outputs;

comparing voltages of the time averaged outputs; and

generating an alert in response to the comparison of the time averaged outputs.

11. The method of detecting a loss of signal of claim 10 wherein the input signal received by the first Gilbert mixer is a differential signal.