Polyphase Implementation of Non-recursive Comb Decimators for Sigma-Delta A/D Converters

Abstract

-In a sigma-delta analog to digital (A/D)As most of the sigma-delta ADC applications require converter, the most computationally intensive block is decimation filters with linear phase characteristics, the decimation filter and its hardware implementation symmetric Finite Impulse Response (FIR) filters are may require millions of transistors. Since these widely used for implementation. But the number of FIR converters are now targeted for a portable application, filter coefficients will be quite large for implementing a a hardware efficient design is an implicit requirement. narrow band decimation filter. Implementing decimation In this effect, this paper presents a computationally filter in several stages reduces the total number of filter efficient polyphase implementation of non-recursive coefficients, and hence reduces the hardware complexity cascaded integrator comb (CIC) decimators for and power consumption [2]. Sigma-Delta Converters (SDCs). The SDCs areThe first stage of decimation filter can be operating at high oversampling frequencies and hence implemented very efficiently using a cascade of integrators require large sampling rate conversions. The filtering and comb filters which do not require multiplication or and rate reduction are performed in several stages to coefficient storage. The remaining filtering is performed reduce hardware complexity and power dissipation. either in single stage or in two stages with more complex The CIC filters are widely adopted as the first stage of FIR or infinite impulse response (IIR) filters according to decimation due to its multiplier free structure. In this the requirements. The amount of passband aliasing or research, the performance of polyphase structure is imaging error can be brought within prescribed bounds by compared with the CICs using recursive and increasing the number of stages in the CIC filter. The non-recursive algorithms in terms of power, speed and width of the passband and the frequency characteristics area. This polyphase implementation offers high speed outside the passband are severely limited. So, CIC filters operation and low power consumption. The polyphase are used to make the transition between high and low implementation of 4th order CIC filter with a sampling rates. Conventional filters operating at low decimation factor of '64' and input word length of sampling rate are used to attain the required transition '4-bits' offers about 70% and 37% of power saving bandwidth and stopband attenuation. compared to the corresponding recursive and Several papers are available in literature that deals non-recursive implementations respectively. The same with different implementations of decimation filter polyphase CIC filter can operate about 7 times faster architecture for sigma-delta ADCs. Hogenauer has than the recursive and about 3.7 times faster than the described the design procedures for decimation and non-recursive CIC filters.interpolation CIC filters with emphasis on frequency response and register width [3]. A power efficien...

Zero-rotation-based nonrecursive comb structure

“…Due to its simplicity, the most popular decimation filter is the comb filter [3]. Its nonrecursive structure has high speed and requires low power consumption [4]- [5]. Considering a decimation factor which can be expressed as power of two 2 , the transfer function is:…”

Power and area efficient comb-based decimator for Sigma-Delta ADCs with high decimation factors

“…However, for large decimation factors, CIC filters present a high power consumption due to the integration section, which works at the highest sampling rate. On the other hand, non-recursive comb filters have been reported consuming less power [3]. The most popular nonrecursive structure uses a decimation factor, M, that can be represented as a power of two, M=2 P .…”

VLSI Implementation of Novel Class of High Speed Pipelined Digital Signal Processing Filter for Wireless Receivers

“…Similar work through the years 2005-2010 also presented (Shahana et al, 2007;Dolecek and Mitra 2008;Sun and Chen, 2008;Mortazavi et al, 2006), to show the efforts that engineers put to increase the CIC filter efficiency for four Generation (4G) filter applications. However, there are inadequate resources regarding high performance decimation filters and enhancement of CIC filter performance is still a challenging task.…”