Real-equivalent-time clock recovery for a nearly-real-time real-equivalent-time oscilloscope

1. A test and measurement device, comprising:

an input port configured to receive a signal from a device under test, the signal having a symbol rate;

one or more analog-to-digital converters to convert the signal to waveform samples at a sampling rate; and

one or more processors configured to execute code that, when aliasing is present, causes the one or more processors to:

determining that aliasing is present when a Nyquist frequency of the sampling rate is less than or equal to a bandwidth of the device and that the sampling rate is greater than the symbol rate;

up-sample a portion of the signal between the Nyquist frequency and the bandwidth having aliased samples to produce up-sampled samples using a sample rate that supports real-time sampling;

use the up-sampled samples to produce a real-time waveform;

perform clock recovery on the real-time waveform to produce a recovered clock; and

resample the aliased samples using the recovered clock to produce a non-aliased waveform.

2. The test and measurement device as claimed in claim 1 , wherein the code that causes the one or more processor to use the up-sampled samples comprises code causes the one or more processors to apply an anti-aliasing filter to the up-sampled samples to produce the real-time waveform.

3. The test and measurement device as claimed in claim 2 , wherein the code that causes the one or more processors to apply an anti-aliasing filter causes the one or more processors to apply a low pass filter.

4. The test and measurement device as claimed in claim 3 , wherein the code that causes the one or more processors to apply the low pass filter comprises code to cause the one or more processors to apply a low pass filter having a bandwidth higher than a Nyquist frequency of the signal, and a stop band frequency of the Nyquist frequency of the samples.

5. The test and measurement device as claimed in claim 3 , wherein the code that causes the one or more processors to apply the low pass filter comprises code to cause the one or more processors to apply a low pass filter having a bandwidth based upon an energy of the signal.

6. The test and measurement device of claim 2 , wherein the code that causes the one or more processors to apply an anti-aliasing filter comprises code that causes the one or more processors to:

apply a first anti-aliasing filter;

after resampling, analyze the signal spectrum; and

apply a second anti-aliasing filter based on the signal spectrum.

7. The test and measurement device as claimed in claim 1 , wherein the code that causes the one or more processors to use the up-sampled samples to produce a real-time waveform comprises code to cause the one or more processors to use interpolation with anti-aliasing protection.

8. The test and measurement device as claimed in claim 7 , wherein the code that causes the one or more processors to use interpolation comprises code to cause the one or more processors to use SINC interpolation with an additional low-pass filter.

9. The test and measurement device as claimed in claim 1 , wherein the code that causes the one or more processors to up-sample the portion of the signal comprises code that causes the one or more processors to up-sample the portion at an up-sample rate of twice or more of the sampling rate.

10. A method of receiving a clock from a waveform, comprising:

receiving a signal from a device under test, the signal having a symbol rate;

converting the signal to waveform samples at a sampling rate;

determining that aliasing is present when a Nyquist frequency of the sampling rate is less than or equal to a bandwidth of the device and that the sampling rate is greater than the symbol rate;

when aliasing is present, up-sampling a portion of the signal between the Nyquist frequency and the bandwidth having aliased samples using a sample rate that supports real-time sampling to produce up-sampled samples;

using the up-sampled samples to produce a real-time waveform;

performing clock recovery on the real-time waveform to produce a recovered clock; and

resampling the aliased samples using the recovered clock to produce a non-aliased waveform.

11. The method as claimed in claim 10 , wherein using the up-sampled samples comprises applying an anti-aliasing filter to the up-sampled samples to produce the real-time waveform.

12. The method as claimed in claim 11 , wherein applying an anti-aliasing filter comprises applying a low pass filter.

13. The method as claimed in claim 12 , wherein applying the low pass filter comprises applying a low pass filter having a bandwidth higher than a Nyquist frequency of the signal, and a stop band frequency of the Nyquist frequency of the samples.

14. The method as claimed in claim 12 , wherein applying the low pass filter comprises applying a low pass filter having a bandwidth based upon an energy of the signal.

15. The method as claimed in claim 11 , wherein applying an anti-aliasing filter comprises:

applying a first anti-aliasing filter;

after resampling, analyzing the signal spectrum; and

applying a second anti-aliasing filter based on the signal spectrum.

16. The method as claimed in claim 10 , wherein using the up-sampled samples to produce a real-time waveform comprises using interpolation with anti-aliasing protection.

17. The method as claimed in claim 16 , wherein using interpolation comprises using SINC interpolation with an additional low-pass filter.

18. The method as claimed in claim 10 , wherein up-sampling the portion of the signal comprises up-sampling the portion at an up-sample rate of twice or more of the sampling rate.