Comparator chain offset reduction
View Patent ↗Comparator chain total offset, static and dynamic, is reduced by injecting a compensation quantity in at least one point in the chain of comparator components. The compensation quantity is determined by providing the comparator chain with calibration signals having equal values and evaluating the output states of the comparator chain. The compensation quantity is adjusted until the probabilities of high and low output states are substantially equal and a calibrated value for the compensation is determined.
1. A calibration system for a comparator chain, comprising:
a comparator configured for receiving a signal including noise;
an unbalancing element coupled to the comparator and configured to add an unbalancing quantity to the signal in at least one point of a comparator chain; and
a compensation circuit coupled to the comparator and the unbalancing element, the compensation circuit configured to monitor output states of the comparator, to determine if the output states are associated with a desired distribution associated with the noise, and if the output states are not associated with the desired distribution associated with the noise, to adjust the unbalancing quantity based on a distribution of the output states.
2. The system of claim 1 , further comprising:
an amplifier coupled between the unbalancing element and the comparator and configured for amplifying the signal.
3. The system of claim 1 , where the comparator is a track-and-latch comparator.
4. The system of claim 1 , where the signal is a differential signal and the comparator is a differential comparator.
5. The system of claim 1 , where the compensating circuit further comprises:
a counter and scale factor block coupled to the comparator and configured to provide a count of output states.
6. The system of claim 5 , where the counter and scale factor block includes an up/down counter for counting output states.
7. The system of claim 6 , where the counter and scale factor block includes scale factor logic coupled to the up/down counter and configured for controlling a speed of convergence of the output states.
8. The system of claim 5 , where the compensation circuit further comprises:
an accumulator coupled to the counter and scale factor block and configured to receive commands from the counter and scale factor block for incrementing, decrementing or maintaining a compensation value.
9. The system of claim 8 , where the compensation circuit further comprises:
a digital-to-analog converter (DAC) coupled to the accumulator and to the unbalancing element, where the DAC is configured to convert the compensation value provided by the accumulator into the unbalancing quantity to be added in the signal.
10. The system of claim 5 , further comprising:
calibration logic coupled to the counter and scale factor block and configured for programming a scale factor in the counter and scale factor block.
11. The system of claim 10 , further comprising:
an amplifier coupled to the unbalancing element and configured for amplifying the signal before the unbalancing quantity is added in to the signal; and
switches coupled to the amplifier and the calibration logic, the switches configured for coupling the signal to the amplifier in response to a calibration control signal generated by the calibration logic.
12. A method of calibrating a comparator chain, comprising:
providing a signal including noise to a comparator chain;
monitoring output decisions of the comparator chain;
determining if the output decisions are associated with a desired distribution associated with the noise; and
if the output decisions are not associated with the desired distribution associated with the noise:
determining an unbalancing quantity based on the monitored output decisions;
adding the unbalancing quantity to the signal in at least one point of the comparator chain; and
repeating the monitoring step.
13. The method of claim 12 , where providing a signal includes providing a differential signal comprising at least two component signals having substantially equal values.
14. The method of claim 12 , where monitoring output decisions and determining whether the output decisions are associated with a desired distribution includes:
counting the number of output decisions; and
comparing the count to at least one threshold value.
15. The method of claim 14 , where comparing the count includes comparing the count to a threshold band.
16. The method of claim 14 , where monitoring output decisions and determining whether the output decisions are associated with a desired distribution further includes:
scaling the count by a scale factor before comparing the count to the at least one threshold value, where the scale factor is programmed for controlling a speed of convergence of the output decisions.