A Third-Order Switched-Current Delta-Sigma Modulator with Analog Error Cancellation Logic and Digital Comb Filter

概要

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This paper presents a fully differential third-order (2-1) switched-current (SI) cascaded delta-sigma modulator (DSM), with an analog error cancellation logic circuit, and a digital decimation filter that is fabricated using 0.18-µm CMOS technology. The 2-1 architecture with only the quantizer input being fed into the second stage is introduced not only to reduce the circuit complexity, but also to be implemented easily using the switched-current approach. Measurements reveal that the dominant error is the quantization error of the second one-bit quantizer (e2). This error can be eliminated using an analog error cancellation logic circuit. In the proposed differential sample-and-hold circuit, low input impedance is presented with feedback and width-length adjustment in SI feedback memory cell (FMC); and that a coupled differential replicate (CDR) common-mode feedforward circuit (CMFF) is used to compensate the error of the current mirror. Also, measurements indicate that the signal-to-noise ratio (SNR), dynamic range (DR), effective number of bits (ENOB), power consumption and chip size are 67.3dB, 69dB, 10.9bits, 12.3mW, and 0.20×0.21mm2, respectively, with a bandwidth of 40kHz, a sampling rate of 10.24MHz, an OSR of 128 and a supply voltage of 1.8V.