Extended frequency-band-decomposition sigma–delta A/D converter

Abstract

Frequency-Band-Decomposition (FBD) is a good candidate to be used to increase the bandwidths of ADC converters based on sigma-delta modulators for software and cognitive radio applications where we need to convert wide bandwidths. Each modulator processes a part of the band of the input signal which is then passed through a digital filter. In the case of large mismatches in the analog modulators, a new solution, called Extended Frequency-Band-Decomposition (EFBD) can be used. As an example, this solution can allow for a 4 % error in the central frequencies without significant degradation of its performance when the digital processing part is paired with the analog modulators. A calibration of the digital part is thus required to reach these theoretical performances. This paper will focus on a self-calibration algorithm for an EFBD. The algorithm helps minimize the quantization noise of the EFBD and helps to flatten the signal transfer function.

A self-calibration scheme for extended frequency-band-decomposition sigma-delta ADC

“…The complete digital processing for one modulator is summarized in Fig. 1, Part C. The frequencies used for demodulation and modulation are expressed as rational numbers so that the sequences are finite and can be stored in a ROM [5].…”

“…It was shown in [5] that an error of 4% in the width of the sub-band (0.05% of the sampling frequency) causes a resolution loss of less than 0.1 bit. Thus, the boundary frequency values (f k r ) can be quantized in this example with a step q s = F s /1024.…”

“…Unfortunately, the modulator transfer functions are not flat. They can be calculated by methods proposed in [20] and, usually, the modulus of the STF can be approximated by a parabola whose maximum is in the modulator band [5]. A corrective filter is applied here to each modulator to flatten its signal transfer function.…”

“…The frequency-band-decomposition (FBD) [1][2][3] is a natural way to widen the bandwidth of sigma-delta converters [4], using parallel bandpass modulators, where each modulator processes a part of the band of the input signal [5]. The main issue of this process is its sensitivity to the central frequencies of the bandpass modulators.…”

“…The main issue of this process is its sensitivity to the central frequencies of the bandpass modulators. Extended frequency-band-decomposition (EFBD) [5] makes it possible to convert a wideband signal, using two extra continuous-time bandpass modulators. This solution is able to adapt to the analog mismatches of the modulators, in order to minimize the quantization noise and to allow for the correct reconstruction of the input signal.…”