Adaptive equalization for calibration of subband hybrid filter banks A/D converters

Abstract

Hybrid Filter Banks (HFB) A/D converters (ADC) are attractive to software-defined radio application, however their high sensitivity to analog imperfections is still a bottleneck for their realization. In this paper, adaptive equalization is applied for calibrating a subband HFB ADC. Thus, the synthesis filter coefficients are iteratively adjusted for compensating the mismatches between the analog part and the digital part. Simulations show that the robustness of subband HFB ADC is therefore improved.

Hybrid Filterbank ADCs With Blind Filterbank Estimation

“…Since the orders of the analysis filterbank filters , are known, we can write a parametric version of , where denotes the vector of numerator and denominator coefficients of the filters , . For a given , we can compute an estimate of up to time as follows: (10) where the the entries , and , of the matrix and the vector , respectively, are defined by (11) (12) with , for any matrix transfer function , and ( denotes the trace operation), for any matrix discrete-time impulse responses and . We can hence define, using (7), a parametric time-varying correlation by (13) Then, the parameters up to time can be estimated by solving the following minimization problem:…”

“…An approach to deal with this uncertainty is to use a reference input signal to estimate the analog filterbank parameters [9]. A similar approach is used in [10]- [12], where instead of estimating the analog filterbank, the digital synthesis bank is directly tuned, via an adaptive filtering technique, to minimize the reconstruction error. However, as pointed out in [13], a blind estimation technique (i.e., one carrying out the estimation without the knowledge of the input signal) is preferred, since it does not interfere with the ADC operation, and is able to track analog parameter drifts during the ADC operation.…”

Synthesis of complex subband Hybrid Filter Banks A/D converters using adaptive filters

“…Synthesis of the complex subband HFB ADC by using complex LMS algorithm. Figure 1 shows the architecture of the complex subband HFB, which reconstruction function [8] can be presented in frequency-domain by…”

“…This method is applied also for synthesizing the subband HFB [6]. We proposed in [8] an adaptive method to compensate analog errors digitally for a subband HFB. Initializing with the precalculated coefficients by the LMSGA method, although the analog errors degrade dramatically the performance of the subband HFB, the iterative adjustments of the synthesis filters can recover a good resolution finally.…”

Hybrid Filter Bank A/D conversion systems applied to future telecommunication scenarios

“…The LMS algorithm has been chosen for its simplicity. This method has been first applied to a subband HFB [6]. Let's consider that the analog center frequencies have been affected by an offset of 1% of the subband bandwidth.…”