A 90 dB SNR, 2.5 MHz output rate ADC using cascaded multibit ΔΣ modulation at 8x oversampling ratio

Abstract

This 16b, 2.5 MHz output rate ADC is intended for xDSL and high-speed instrumentation applications. A fourth-order cascaded /spl Delta//spl Sigma/ modulator (/spl Delta//spl Sigma/M) operating at 20 MHz employs multibit quantization and dynamic element matching (DEM) to make all quantization noise contributions negligible at an oversampling ratio (OSR) of eight. The ADC achieves 90 dB signal-to-noise ratio (SNR) in a 1.25 MHz bandwidth, and 102 dB spurious free dynamic range (SFDR) with 270 mW dissipation.