In this paper, a new multi loop sigma‐delta (ΣΔ) modulator is proposed which employs one order redundant noise shaping in the first stage so the effect of the quantization noise leakage is minimized. Thus, analog circuit requirements are considerably relaxed compared to the conventional Multi‐stAge‐noise‐SHaping (MASH) structures. This enhancement makes the structure appropriate for low voltage and broadband applications. The proposed architecture is compared with traditional high‐order structures, and the advantages are demonstrated by both the analysis and behavioral system level simulations. As a prototype, the proposed MASH 3–2 sigma‐delta modulator is designed, and the detailed design procedure is presented from the system level to the circuit level in a 90 nm CMOS technology. Circuit level simulation results show that the modulator achieves a peak signal‐to‐noise and distortion ratio of 79.4 dB and 79 dB dynamic range over a 10 MHz bandwidth with a sampling frequency of 160 MHz. It consumes 35.4 mW power from a single 1 V supply. Copyright © 2012 John Wiley & Sons, Ltd.

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A discrete-time charge-domain filter is proposed, which can realise complex conjugate poles in the transfer function of the filter. By employing a second transconductance in the feedback path of a second-order infinite impulse response charge-domain filter, it is proved that the filter topology is capable of implementing complex poles. This method makes charge-sampling filters more efficient in designing frequency-domain filters where they can be used to synthesise any type of filter structures such as Butterworth, Chebyshev and so on.Introduction: Discrete-time (DT) charge-sampling filters have recently become an efficient structure for use in software-defined radio applications because of their unique properties of programmability. The charge-sampling technique provides a lowpass continuous-time (CT) sinc function by integration of the input current in a fixed time window. Also, two types of discrete-time filters, the infinite impulse response (IIR) and the finite impulse response (FIR) filters can be realised with charge-sampling filters where the transfer function of the filter embeds the FIR or IIR response into the sinc function [1]. Various FIR and IIR charge-domain filters of different orders have been implemented [2][3][4][5]. IIR filters can achieve higher stopband rejection compared with FIR filters of the same order and therefore they are preferred over the FIR ones. The transfer function of a higher-order IIR filter can be implemented by cascading DT integrators. Nevertheless, cascading integrators will not lead to a general IIR transfer function since all of the poles in the transfer function are real. In this Letter, we propose a second-order IIR structure that can realise complex poles in its transfer function. This structure can be used to synthesise the versatility of filter topologies.

SummaryThis paper proposes a discrete‐time charge domain filter that achieves complex conjugate poles in the transfer function of the filter. To achieve complex conjugate poles, local feedbacks are inserted around two successive discrete‐time integrators. The feedback path is implemented through a transconductance cell which applies a continuous time current into the integrators. Analytical models have been proposed to approximate the behavior of the filter. These models confirm that the structure is capable of realizing complex poles and thus can be used to synthesize any type of filter structures such as Butterworth, Chebysheve, etc. To show the effectiveness of the proposed architecture, Butterworth filters of order 2 and 4 operating at 50MS/s are designed and implemented in 180‐nm CMOS technology with 1.8‐V power supply. The effect of circuit nonidealities on the performance of the filter is analyzed and verified through simulations. Simulation results show that a conventional charge domain filter can be simply extended to implement complex conjugate poles while the noise and linearity performance of the filter are also improved. Copyright © 2016 John Wiley & Sons, Ltd.