DeSerializer DC offset adaptation based on decision feedback equalizer adaptation
View Patent ↗An apparatus for processing data includes a decision feedback equalizer configured to sample an analog signal to yield digital data and a DC offset adaptation circuit. The decision feedback equalizer is configured to sample the equalized signal using at least one data latch at a first data latch threshold value and at a second data latch threshold value. The DC off set adaptation circuit is configured to calculate a DC off set in the analog signal based on the first data latch threshold value and on the second data latch threshold value.
1. An apparatus for processing data, comprising:
a decision feedback equalizer configured to sample an analog signal to yield digital data, wherein the decision feedback equalizer samples the analog signal with at least one data latch configured at a first data latch threshold value and at a second data latch threshold value; and
a DC offset adaptation circuit configured to calculate a DC offset in the analog signal based on the first data latch threshold value and on the second data latch threshold value, wherein the DC offset adaptation circuit is configured to calculate the DC offset as half a sum of the first data latch threshold value and the second data latch threshold value.
2. The apparatus of claim 1 , further comprising a DC offset cancellation circuit configured to remove the DC offset from the analog signal.
3. The apparatus of claim 2 , further comprising a continuous time linear equalizer configured to equalize the analog signal to yield an equalized signal to be sampled by the decision feedback equalizer.
4. The apparatus of claim 3 , wherein the DC offset cancellation is upstream from the continuous time linear equalizer.
5. The apparatus of claim 2 , further comprising a digital to analog converter configured to convert the DC offset from a digital value to an analog value before removing the DC offset from the analog signal.
6. The apparatus of claim 2 , wherein the DC offset adaptation circuit is disabled after calculating the DC offset.
7. The apparatus of claim 1 , wherein the decision feedback equalizer is configured to shift the first data latch threshold value and the second data latch threshold value based on the DC offset calculated by the DC offset adaptation circuit.
8. The apparatus of claim 7 , wherein the DC offset is substantially removed from the digital data by shifting the first data latch threshold value and the second data latch threshold value in the decision feedback equalizer based on the DC offset calculated by the DC offset adaptation circuit.
9. The apparatus of claim 1 , wherein the at least one data latch comprises a first data latch configured to sample the analog signal using the first data latch threshold value and a second data latch configured to sample the equalized signal using the second data latch threshold value.
10. The apparatus of claim 1 , further comprising a decision level adaptation circuit configured to adapt a plurality of error latch threshold values, each based on a different data pattern in the digital data.
11. The apparatus of claim 10 , wherein the plurality of error latch threshold values comprises a first error latch threshold value, a second error latch threshold value, a third error latch threshold value and a fourth error latch threshold value, and wherein the decision level adaptation circuit is configured to adapt the first data latch threshold value based on the first error latch threshold value and the second error latch threshold value, and to adapt the second data latch threshold value based on the third error latch threshold value and the fourth error latch threshold value.
12. The apparatus of claim 11 , wherein the decision level adaptation circuit is configured to calculate the first data latch threshold value as half a sum of the first error latch threshold value and the second error latch threshold value, and to calculate the second data latch threshold value as half a sum of the third error latch threshold value and the fourth error latch threshold value.
13. The apparatus of claim 11 , wherein the decision level adaptation circuit is configured to adapt the first error latch threshold value based on a level of the analog signal for a data pattern of ‘110’ in the digital data, to adapt the second error latch threshold value based on a level of the analog signal for a data pattern of ‘101’ in the digital data, to adapt the third error latch threshold value based on a level of the analog signal for a data pattern of ‘001’ in the digital data, and to adapt the fourth error latch threshold value based on a level of the analog signal for a data pattern of ‘010’ in the digital data.
14. The apparatus of claim 1 , wherein the apparatus comprises a serializer/deserializer receiver.
15. A method for deserializing data, comprising:
sampling an analog signal at a first data latch threshold value and at a second data latch threshold value in a decision feedback equalizer circuit to yield digital data, wherein the first data latch threshold value is calculated based on levels of the analog signal for first and second patterns in the digital data, and wherein the second data latch threshold value is calculated based on levels of the analog signal for third and fourth patterns in the digital data; and
calculating a DC offset in the analog signal based on half a sum of the first data latch threshold value and the second data latch threshold value.
16. The method of claim 15 , further comprising converting the DC offset to an analog value and subtracting the analog value of the DC offset from the analog signal upstream from the decision feedback equalizer circuit.
17. The method of claim 16 , wherein the DC offset is calculated in open-loop fashion.
18. The method of claim 15 , further comprising shifting the first data latch threshold value and the second data latch threshold value in the decision feedback equalizer circuit based on the DC offset to remove the DC offset from the digital data.
19. A deserializer receiver comprising:
decision feedback equalizer means for sampling an analog signal to yield digital data, wherein the decision feedback equalizer samples the analog signal with at least one data latch configured at a first data latch threshold value and at a second data latch threshold value; and
DC offset adaptation means for calculating a DC offset in the analog signal based on the first data latch threshold value and on the second data latch threshold value, wherein a first data latch is configured to sample the analog signal using the first data latch threshold value and a second data latch is configured to sample the analog signal using the second data latch threshold value.
20. The deserializer receiver of claim 19 , wherein the DC offset adaptation means is configured to calculate the DC offset as half a sum of the first data latch threshold value and the second data latch threshold value.