A 10-MHz multi-bit MASH delta–sigma modulator with analog summing interstage

Abstract

This paper presents an improved 4-bit twostage multi-stage noise shaping (MASH) delta-sigma modulator (DSM). The two-stage MASH DSM utilizes the second-order chain of cascade of integrators with feedforward (CIFF) and the cascade of integrators with distributed feedback (CIFB) architectures for the first and second stages, respectively. The 4-bit CIFF requires an active adder, which is conventionally implemented with a highbandwidth high-swing amplifier. In the proposed DSM, the active adder is eliminated and the adder-less integrator is applied in the first stage of the MASH DSM. The first stage quantization noise, which is fed to the second stage, is conventionally extracted from the analog input and digital output of the quantizer in the first stage. The number of quantizer digital output paths increases exponentially with the quantization bit number. A large number of DAC feedback paths in the interstage is avoided by proposing a new interstage topology based on analog summing to derive the first stage quantization noise in the analog domain. The prototype DSM is fabricated in a 0.11-lm CMOS process. When operating from a 1.2-V supply, the modulator achieves 67.8-dB peak SNDR, while consuming 25 mW, with an OSR of 8 at a 160-MHz sampling frequency.

A 103 dB DR Fourth-Order Delta-Sigma Modulator for Sensor Applications

“…The fourth-order DSM is designed to achieve a high resolution. The DSM architecture types can be divided mainly into CIFF architecture and cascade-of-integrators with feedback (CIFB) architecture [8,9]. CIFF architecture was selected for the DSM in this paper.…”

“…The output voltage swing of each integrator is reduced through the feedforward path of the modulator. Therefore, the requirement for the voltage headroom and slew rate of the operational transconductance amplifier (OTA) is relaxed, which represents an advantage over the CIFB architecture in terms of power efficiency [8,9]. Due to the small magnitude of the electromyogram signal, an amplifier must be used to amplify the electromyogram signal so that the ADC can process it, as shown in Figure 1.…”

“…Internal feedback (g1) was added between the third integrator and the fourth integrator in the loop filter. Internal feedback reduces noise power to improve the signal-to-noise ratio (SNR) because it creates a value of zero near the signal band in the noise transfer function (NTF) [9]. Internal feedback (g1) was added between the third integrator and the fourth integrator in the loop filter.…”