Measuring impairments of digitized signals in data and timing recovery circuits
View Patent ↗On-chip at-speed eye measurements of digitized signals in data and timing recovery circuits are disclosed. Eye diagrams and jitter measurements are used to evaluate signal quality and bath-tub Bit Error Rate characteristics in baseband communication systems. This disclosure describes a method and apparatus for digitally sampling a received signal at speed to produce an eye diagram of the received signal. This involves adding a small amount of circuitry to the existing prior art systems that use an interpolator for timing recovery and data recovery. In the present disclosure a temporary offset is applied to the interpolation index of the interpolator to obtain interpolated samples between the baud center and baud edge. The eye diagram can be produced from the received digitized and interpolated signal before equalization, or alternatively from the equalized signal.
1. A method for measuring signal impairments in a received signal in an asynchronous Digital Signal Processing (DSP) based data and timing recovery circuit, comprising:
generating an offset value;
applying the offset value to an interpolation index to obtain, at a baud speed of the received signal, offset interpolated samples between a baud centre and a baud edge;
processing the offset interpolated samples at a processing rate lower than the baud speed of the received signal; and
determining, within the DSP based data and timing recovery circuit, signal characteristics in the received signal based on the offset interpolated samples.
2. The method of claim 1 , wherein the signal characteristics comprise signal amplitude.
3. The method of claim 1 , wherein applying the offset to the interpolation index comprises offsetting a baud-edge sampling, while maintaining a baud-center sampling without offset.
4. The method of claim 1 , wherein applying the offset to the interpolation index comprises offsetting a baud-center sampling, while maintaining a baud-edge sampling without offset.
5. The method of claim 1 further comprising:
collecting two dimensional histogram statistics of the interpolated samples, to obtain stored offset interpolated samples; and
processing the stored offset interpolated samples at the processing rate lower than the baud speed of the received signal.
6. The method of claim 1 , further comprising:
generating an eye diagram from the received signal and the stored offset interpolated samples for measuring signal impairments in the received signal.
7. The method of claim 6 , wherein the eye diagram is generated using the received signal prior to equalization.
8. The method of claim 6 , wherein the eye diagram is generated using the received signal after equalization.
9. The method of claim 1 , wherein measuring signal impairments includes calculating signal jitter and bath-tub bit error rates.
10. The method of claim 1 , wherein the offset to the interpolation index is applied in relation to properties of the received signal.
11. The method of claim 10 , wherein the offset to the interpolation index is applied at a selected frequency and for a selected duration based on synchronization parameters of the received signal.
12. A method for measuring signal impairments in a received signal in a synchronous Digital Signal Processing (DSP) based data and timing recovery circuit, comprising:
generating an offset value;
applying the offset value to a timing control signal to obtain, at a baud speed of the received signal, offset timing control signals between a baud centre and a baud edge;
processing the offset timing control signals at a processing rate lower than the baud speed of the received signal; and
determining, within the DSP based data and timing recovery circuit, signal impairments in the received signal based on the offset timing control signals.
13. A non-transitory computer-readable medium storing statements and instructions for execution by a processor to perform a method for measuring signal impairments in a received signal in an asynchronous Digital Signal Processing (DSP) based data and timing recovery circuit, the method comprising:
generating an offset value;
applying the offset value to an interpolation index to obtain, at a baud speed of the received signal, offset interpolated samples between a baud centre and a baud edge;
processing the offset interpolated samples at a processing rate lower than the baud speed of the received signal; and
determining, within the DSP based data and timing recovery circuit, signal characteristics in the received signal based on the offset interpolated samples.
14. The non-transitory computer-readable medium of claim 13 , wherein the signal characteristics comprise signal amplitude.
15. The non-transitory computer-readable medium of claim 13 , wherein applying the offset to the interpolation index comprises offsetting a baud-edge sampling, while maintaining a baud-center sampling without offset.
16. The non-transitory computer-readable medium of claim 13 , wherein applying the offset to the interpolation index comprises offsetting a baud-center sampling, while maintaining a baud-edge sampling without offset.
17. The non-transitory computer-readable medium of claim 13 , wherein the method further comprises:
generating an eye diagram from the received signal and the offset interpolated samples for measuring signal impairments in the received signal.
18. The non-transitory computer-readable medium of claim 13 , wherein the offset to the interpolation index is applied in relation to properties of the received signal.