Interface with variable data rate
A device includes a transmitter coupled to a node, where the node is to couple to a wired link. The transmitter has a plurality of modes of operation including a calibration mode in which a range of communication data rates over the wired link is determined in accordance with a voltage margin corresponding to the wired link at a predetermined error rate. The range of communication data rates includes a maximum data rate, which can be a non-integer multiple of an initial data rate.
1. A device, comprising:
a receive circuit configured to receive data signals; and
control logic configured to:
determine a first offset voltage of the receive circuit, wherein the first offset voltage corresponds to a first error rate of the receive circuit;
determine a second offset voltage of the receive circuit, wherein the second offset voltage corresponds to a second error rate of the receive circuit that is lower than the first error rate of the receive circuit;
determine a noise metric in accordance with the first offset voltage and the second offset voltage; and
determine a predicted third offset voltage of the receive circuit in accordance with the noise metric and the second offset voltage, wherein the third offset voltage corresponds to a third error rate of the receive circuit, wherein the third error rate corresponds to a target error rate and the predicted third offset voltage corresponds to a voltage margin;
wherein the receive circuit is configured to receive data signals utilizing a voltage margin parameter corresponding to the predicted third offset voltage, to produce output signals, output by the receive circuit.
2. The device of claim 1 , wherein the control logic is configured to execute instructions for characterizing the receive circuit, the instructions including:
instructions for determining a first offset voltage of the receive circuit, wherein the first offset voltage corresponds to a first error rate of the receive circuit;
instructions for determining a second offset voltage of the receive circuit, wherein the second offset voltage corresponds to a second error rate of the receive circuit that is lower than the first error rate of the receive circuit;
instructions for determining a noise metric in accordance with the first offset voltage and the second offset voltage; and
instructions for determining a predicted third offset voltage of the receive circuit in accordance with the noise metric and the second offset voltage, wherein the third offset voltage corresponds to a third error rate of the receive circuit, wherein the third error rate corresponds to a target error rate and the predicted third offset voltage corresponds to a voltage margin.
3. The device of claim 1 , wherein the control circuit is further configured to estimate a voltage margin based on the third offset voltage, wherein the voltage margin parameter corresponds to the estimated voltage margin.
4. The device of claim 1 , wherein the control logic is configured to determine a respective offset voltage of the first offset voltage and second offset voltage by determining a response of the receive circuit at a sequence of voltages.
5. The device of claim 1 , wherein the control logic is configured to determine the third offset voltage in accordance with a formula of the form V3=V2−αN, where V2 is the second offset voltage, N is a noise metric, and α is a coefficient determined in accordance with the second error rate and the target error rate.
6. The device of claim 1 , wherein the control logic is configured to determine the third offset voltage in accordance with a formula of the form V3=V4−αN, where N is a noise metric determined while the receive circuit receives a periodic signal, and α is a coefficient determined in accordance with the second error rate and the target error rate, and V4 is the second offset voltage, determined while the receive circuit receives a pseudo-random data signal and experiences the second error rate.
7. A method of operating an electronic device having a receive circuit and a control circuit, comprising:
determining a first offset voltage of the receive circuit, wherein the first offset voltage corresponds to a first error rate of the receive circuit;
determining a second offset voltage of the receive circuit, wherein the second offset voltage corresponds to a second error rate of the receive circuit that is lower than the first error rate of the receive circuit;
determining a noise metric in accordance with the first offset voltage and the second offset voltage;
determining a predicted third offset voltage of the receive circuit in accordance with the noise metric and the second offset voltage, wherein the third offset voltage corresponds to a third error rate of the receive circuit, wherein the third error rate corresponds to a target error rate and the predicted third offset voltage corresponds to a voltage margin; and
receiving data signals using the receive circuit, utilizing a voltage margin parameter corresponding to the predicted third offset voltage, to produce output signals, output by the receive circuit.
8. The method of claim 7 , further comprising estimating a voltage margin based on the third offset voltage, wherein the voltage margin parameter corresponds to the estimated voltage margin.
9. The method of claim 7 , wherein determining a respective offset voltage of the first offset voltage and second offset voltage includes determining a response of the receive circuit at a sequence of voltages.
10. The method of claim 7 , wherein the third offset voltage is determined in accordance with a formula of the form V3=V2−αN, where V2 is the second offset voltage, N is a noise metric, and α is a coefficient determined in accordance with the second error rate and the target error rate.
11. The method of claim 7 , wherein the third offset voltage is determined in accordance with a formula of the form V3=V4−αN, where N is a noise metric determined while the receive circuit receives a periodic signal, and α is a coefficient determined in accordance with the second error rate and the target error rate, and V4 is the second offset voltage, determined while the receive circuit receives a pseudo-random data signal and experiences the second error rate.
12. The method of claim 11 , wherein the periodic data signal has a fundamental frequency equal to a clock frequency of the receive circuit.
13. The method of claim 7 , wherein a ratio of the first error rate to the second error rate is at least 100.
14. The method of claim 7 , wherein determining the noise metric and determining the predicted third offset voltage of the receive circuit are further in accordance with a predefined relationship between error rate and signal-to-noise ratio.
15. The method of claim 14 , wherein the predefined relationship is
ER
=
0.5
erfc
(
V
SNR
2
)
,
where ER is the error rate, erfc is a predefined complementary error function, and V SNR is a voltage signal-to-noise ratio associated with a system that includes the receive circuit.
16. The method of claim 14 , wherein receiving data using the receive circuit, utilizing a voltage margin parameter corresponding to a respective offset voltage includes changing a threshold of the receive circuit in accordance with the voltage margin parameter.
17. The method of claim 7 , wherein the first offset voltage or second offset voltage is determined using a pseudo-random sequence of data signals received by the receive circuit.
18. The method of claim 7 , further comprising adjusting a supply voltage of a transmit circuit that sends the data signals to the receive circuit.
19. The method of claim 7 , further comprising adjusting a voltage swing of the data signals received by the receive circuit.
20. A device, comprising:
a receive circuit configured to receive data signals; and
control means, coupled to the receive circuit, for configuring the receive circuit to operate in accordance with a target error rate, including means for:
determining a first offset voltage of the receive circuit, wherein the first offset voltage corresponds to a first error rate of the receive circuit;
determining a second offset voltage of the receive circuit, wherein the second offset voltage corresponds to a second error rate of the receive circuit that is lower than the first error rate of the receive circuit;
determining a noise metric in accordance with the first offset voltage and the second offset voltage; and
determining a predicted third offset voltage of the receive circuit in accordance with the noise metric and the second offset voltage, wherein the third offset voltage corresponds to a third error rate of the receive circuit, wherein the third error rate corresponds to a target error rate and the predicted third offset voltage corresponds to a voltage margin;
wherein the receive circuit is configured to receive data signals utilizing a voltage margin parameter corresponding to the predicted third offset voltage, to produce output signals, output by the receive circuit.