Low power signaling interface
In a chip-to-chip signaling system includes at least one signaling link coupled between first and second ICs, the first IC has an interface coupled to the signaling link and timed by a first interface timing signal. The second IC has an interface coupled to the signaling link and timed by a second interface timing signal that is mesochronous with respect to the first interface timing signal. The second IC further has phase adjustment circuitry that adjusts a phase of the second interface timing signal using a digital counter implemented with Josephson-junction circuit elements.
1. A method of operation within an integrated circuit device, the method comprising:
incrementing a modulo-N phase count in response to respective timing events within a first timing signal such that the phase count repeatedly sequences between N discrete values, N being an integer greater than 4;
after each phase-count increment, comparing the phase count to a match count having a value between 0 and N to produce, as a second timing signal, a match-result signal that indicates a match once for each repetition of the N discrete values of the phase count; and
sampling a data signal received via a signaling link external to the integrated circuit device in response to the second timing signal.
2. The method of claim 1 further comprising adjusting the match count to adjust a phase-offset of the second timing signal with respect to the data signal.
3. The method of claim 2 further comprising determining at least one boundary phase-offset of the second timing signal that, when applied to sample the data signal, yields a bit error rate greater than a predetermined threshold, and wherein adjusting the match count comprises adjusting the match count in accordance with the boundary phase-offset.
4. The method of claim 1 wherein the frequency of the first timing signal is an integer multiple of a data rate of the data signal.
5. The method of claim 1 wherein the frequency of the first timing signal is a non-integer multiple of a data rate of the data signal.
6. The method of claim 1 wherein N is subject to change during operation of the integrated circuit device due to change in voltage and/or temperature.
7. The method of claim 1 further comprising generating, in response to each of the timing events within the first timing signal, a plurality of asynchronous timing pulses, and wherein incrementing the phase count in response to respective timing events within the first timing signal comprises propagating the phase count through a plurality of logic elements at times controlled by the asynchronous timing pulses to generate an incremented phase count.
8. An integrated circuit device comprising:
a modulo-N phase counter to increment a phase count in response to respective timing events of a first timing signal such that the phase count repeatedly sequences between N discrete values, N being an integer greater than 4;
a comparator that compares the phase count, after each increment thereof, to a match count having a value between 0 and N to produce, as a second timing signal, a match-result signal that indicates a match once for each repetition of the N discrete values of the phase count; and
sampling circuitry to sample a data signal received via a signaling link external to the integrated circuit device in response to the second timing signal.
9. The integrated circuit device of claim 8 further comprising timing-calibration circuitry that adjusts the match count to change a phase-offset of the second timing signal with respect to the data signal.
10. The integrated circuit device of claim 9 wherein the timing-calibration circuitry comprises circuitry to (i) determine at least one boundary phase-offset of the second timing signal that, when applied to sample the data signal, yields a bit error rate greater than a predetermined threshold, and (ii) adjust the match count in accordance with the boundary phase-offset.
11. The integrated circuit device of claim 8 wherein the frequency of the first timing signal is an integer multiple of a data rate of the data signal.
12. The integrated circuit device of claim 8 wherein the frequency of the first timing signal is a non-integer multiple of a data rate of the data signal.
13. The integrated circuit device of claim 8 wherein N is subject to change during operation of the integrated circuit device due to change in voltage and/or temperature.
14. The integrated circuit device of claim 8 further comprising self-timing pulse generating circuitry to generate, in response to each of the timing events within the first timing signal, a plurality of asynchronous timing pulses that enable operation of the phase counter and comparator.