Design and Simulation of Fourth-Order Delta-Sigma Modulator-MASH Architecture
The delta-sigma modulator is used as an oversampling ADC, which processes the signal input and the quantization noise by two distinct transfer functions, thus, separating the signal and noise into two distinct frequency bands. The resulting output of the
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Abstract The delta-sigma modulator is used as an oversampling ADC, which processes the signal input and the quantization noise by two distinct transfer functions, thus, separating the signal and noise into two distinct frequency bands. The resulting output of the modulator is digitally processed to separate the signal from noise. The performance of the ADC can be improved by increasing the order of the modulator, which imposes constraints on the system stability and on the input signal range. This paper examines the issues related to the design of a stable fourth-order MultistAge noise SHaping architecture(MASH) ADC, using two second-order deltasigma modulators in cascade. The architecture achieves second-order Signal Transfer Function (STF) with fourth-order noise shaping . The modulator employs 32 MHz— clock, to obtain 8-bit sample sequence at 128 kHz sample rate. The resulting output is processed by a digital low pass filter to separate the signal from noise. The FIR filter is implemented using frequency sampling technique. Keywords Oversampling · Noise shaping · Quantization noise · Linear model · Stability · Filter
1 Introduction Analog to digital converters (ADC) are of two types: Nyquist rate ADC and oversampling ADC. In the former, the minimum sampling frequency is defined to be twice the bandwidth of the analog input (f s = 2f b , where f b is the input signal bandwidth) (Fig. 1).
S. S. Kotabagi (B) School of Electronics, KLE Technological University, Hubli, India e-mail: [email protected] P. Subbanna Bhat School of Electronics and Communication, KLE Technological University, Hubli, India e-mail: [email protected] © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021 V. Nath and J. K. Mandal (eds.), Nanoelectronics, Circuits and Communication Systems, Lecture Notes in Electrical Engineering 692, https://doi.org/10.1007/978-981-15-7486-3_54
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Fig. 1 Nyquist rate ADC
Fig. 2 Oversampling ADC
The oversampling ADC (Fig. 2) samples the analog signal at a rate much higher than the Nyquist rate, which is exploited to reduce the quantization noise in the signal bandwidth [1]. The delta-sigma modulator is a closed loop system, which processes the signal and quantization noise differently using Signal Transfer Function (STF) and Noise Transfer Function (NTF), which results in confining the signal and noise into two mutually exclusive frequency bands and this is known as noise shaping. The output of the modulator is in digital form, containing both the signal and quantization noise, which is filtered using Digital Signal Processing (DSP) to obtain the digital encoding of the signal input [1].The performance of delta-sigma ADC can be improved in three ways: (i)
By increasing the sampling rate. Since the (quantization) noise is distributed uniformly across sampling frequency range, with the increase in the sampling rate, noise content within the signal bandwidth is reduced. (ii) By enhancing the reso
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