SR latch circuit with single gate delay

1. An SR latch circuit having an enable input and an SR latch circuit output, the SR latch circuit comprising:

a first input stage having an input for receiving a set input and having an output for producing a first component of the SR latch circuit output, the first input stage configured to receive an enable input in advance of set and reset inputs becoming valid, the enable input causing the first input stage to become transparent while enabled, the first input stage having a single gate delay between the input of the first input stage and the output of the first input stage;

a second input stage having an input for receiving a reset input and having an output for producing a second component of the SR latch circuit output, the second input stage configured to receive the enable input in advance of set and reset inputs becoming valid, the enable input causing the second input stage to become transparent while enabled, the second input stage having a single gate delay between the input of the second input stage and the output of the second input stage.

2. The latch circuit of claim 1 further comprising:

an input generating circuit that generates the set and reset inputs as RZ (return to zero) signals that are timed to become valid after the enable input has caused the input stages to become transparent.

3. The latch circuit of claim 2 wherein the input generating circuit comprises a strong-arm slicer circuit that generates the set and reset inputs.

4. The latch circuit of claim 1 further comprising:

a storage circuit connected to the output of the first input stage and the output of the second input stage.

5. The latch circuit of claim 1 configured for return-to-zero signaling for set and reset inputs, and for non-return-to-zero signaling for the SR latch circuit output.

6. The latch circuit of claim 1 wherein the input stages have a transparent state activated by the enable input, and the input stages are configured so as to overpower the storage circuit while in the transparent state.

7. The latch circuit of claim 2 wherein the input generating circuit generates only valid combinations of enable input and the set and reset inputs for the SR latch circuit, wherein the valid combinations comprise:

for enable active low:

Enb

Set

Reset

on

op

Valid states

0

0

1

1

0

0

1

0

0

1

1

0

0

p

p

OR

for enable active high:

Enb

Set

Reset

on

op

Valid states

1

0

1

0

1

1

1

0

1

0

0

1

1

p

p

8. The latch circuit of claim 4 wherein the storage circuit comprises cross-coupled inverters.

9. An integrated circuit comprising the latch circuit of claim 1 .

10. A serializer deserializer comprising the latch circuit of claim 1 .

11. A system comprising:

a first circuit board;

a second circuit board connected to the first circuit board;

a plurality of serial interconnections, each serial interconnection interconnecting a respective pair of components in the system;

for each of at least one of the serial interconnections, a respective serializer deserializer in accordance with claim 10 .

12. A serializer deserializer comprising a decision feedback equalizer, the decision feedback equalizer comprising an SR latch circuit having an enable input and an SR latch circuit output, the SR latch circuit comprising:

a first input stage having an input for receiving a set input and having an output for producing a first component of the SR latch circuit output, the first input stage configured to receive an enable input in advance of set and reset inputs becoming valid, the enable input causing the first input stage to become transparent while enabled, the first input stage having a single gate delay between the input of the first input stage and the output of the first input stage; and

a second input stage having an input for receiving a reset input and having an output for producing a second component of the SR latch circuit output, the second input stage configured to receive the enable input in advance of set and reset inputs becoming valid, the enable input causing the second input stage to become transparent while enabled, the second input stage having a single gate delay between the input of the second input stage and the output of the second input stage.

13. A system comprising:

a first circuit board;

a second circuit board connected to the first circuit board;

a plurality of serial interconnections, each serial interconnection interconnecting a respective pair of components in the system;

for each of at least one of the serial interconnections, a respective serializer deserializer in accordance with claim 12 .

14. An input circuit for an SR latch, the input stage circuit comprising:

a first inverter circuit for receiving a reset input;

a second inverter circuit for receiving a set input;

an enable circuit configured to enable the inverter circuits such that while disabled, each inverter can pull a high input low, but cannot pull a low input high;

an input generating circuit that generates the set and reset inputs as RZ (return to zero) signals that are timed to become valid after the enable input has enabled the first and second inverter circuits.

15. The input circuit of claim 14 wherein the first inverter circuit is a part of a first input stage and the second inverter circuit is a part of a second input stage, and the input generating circuit generates the set input and the reset inputs as RZ (return to zero) signals that are timed to become valid after the enable input has caused the input stages to become transparent.

16. The input circuit of claim 15 wherein the input generating circuit comprises a strong-arm slicer circuit that generates the set and reset inputs.

17. The input circuit of claim 14 further comprising:

a storage circuit connected to the output of the first input stage and the output of the second input stage.

18. The input circuit of claim 14 configured for return-to-zero signaling for set and reset inputs, and for non-return-to-zero signaling for the SR latch circuit output.

19. The input circuit of claim 14 wherein the first inverter circuit is a part of a first input stage and the second inverter circuit is a part of a second input stage, and the input stages have a transparent state activated by the enable input, and the input stages are configured so as to overpower the storage circuit while in the transparent state.

20. The input circuit of claim 15 wherein the input generating circuit generates only valid combinations of enable input and the set and reset inputs for the SR latch circuit, wherein the valid combinations comprise:

for enable active low:

Enb

Set

Reset

on

op

Valid states

0

0

1

1

0

0

1

0

0

1

1

0

0

p

p

OR

for enable active high:

Enb

Set

Reset

on

op

Valid states

1

0

1

0

1

1

1

0

1

0

0

1

1

p

p

21. The input circuit of claim 17 wherein the storage circuit comprises cross-coupled inverters.

22. An integrated circuit comprising the input circuit of claim 14 .

23. An input circuit for an SR latch circuit having an enable input and an SR latch circuit output, the input circuit comprising:

a first input stage having an input for receiving a set input and having an output for producing a first component of the SR latch circuit output, the first input stage having only one transistor that receives the enable input, the first input stage becoming transparent while enabled, the first input stage having a single gate delay between the input of the first input stage and the output of the first input stage;

a second input stage having an input for receiving a reset input and having an output for producing a second component of the SR latch circuit output, the second input stage having only one transistor that receives the enable input, the second input stage becoming transparent while enabled, the second input stage having a single gate delay between the input of the second input stage and the output of the second input stage.

24. An integrated circuit comprising the input circuit of claim 23 .