Estimation of timing errors in a time-interleaved analog to digital converter system
A method for estimating a relative time difference vector in a group of digitized signals from a time interleaved analog-to-digital module having a plurality of parallel and time interleaved analog-to-digital converters. The method comprises the steps of selecting (S 1 ) one of said digitized signals as a reference signal, calculating (S 2 -S 3 ) an actual time delay between each of the remaining signals and said reference signal, and subtracting (S 4 ), for each of said remaining signals, an intended interleaving time delay from said time delay. In order for this method to provide the correct estimate, the signal must be bandlimited, not only to the system bandwidth, but to the bandwidth of one ADC. However, given this bandwidth limitation, the estimation is very precise, and therefore enables reconstruction of the digitized signal without feedback.
1. A method for estimating a relative time difference vector in a group of digitized signals from a time interleaved analog-to-digital module having a plurality of parallel and time interleaved analog-to-digital converters, said method comprising:
selecting one of said digitized signals as a reference signal,
calculating an actual time delay between each of the remaining digitized signals and said reference signal, and
subtracting, for each of said remaining digitized signals, an intended interleaving time delay from said actual time delay.
2. The method according to claim 1 , wherein said actual time delay is calculated by defining a loss function as a measure of a difference between sequences as a function of the delay therebetween, and minimizing the loss function.
3. The method according to claim 2 , wherein the step of defining the loss function comprises applying a delay to each of said remaining digitized signals and thereby forming a delayed signal.
4. The method according to claim 3 , wherein said delay is applied using a fractional delay filter.
5. A method according to claim 4 , wherein said fractional delay filter is implemented using at least one of Lagrange, Farrow Structure and Thiran Allpass.
6. The method according to claim 1 , wherein the loss function is defined as a sum over an ensemble of samples of squared differences between said delayed signal and said reference signal.
7. An estimation module for estimating a relative time difference vector in a group of digitized signals from a time interleaved analog-to-digital module having a plurality of parallel and time interleaved analog-to-digital converters, said estimation module being adapted to
select one of said digitized signals as a reference signal,
calculate an actual time delay between each of the remaining digitized signals and said reference signal, and
subtract, for each of said remaining digitized signals, an intended interleaving time delay from said actual time delay.
8. A system for deskewing relative time errors in a group of digitized signals from a time interleaved analog-to-digital module having a plurality of parallel and time interleaved analog-to-digital converters, comprising:
an estimation module according to claim 7 ,
a filter coefficient calculation module, arranged to calculate time-deskew filter coefficients based on said relative time-deskew vector, and
a digital time deskew filter module, arranged to apply said filter coefficients to the digitized signals from the analog-to-digital module.