A cyclic A/D converter that does not require ratio-matched components

The circuit configuration of a cyclic analog-to-digital (A/D) converter using switched-capacitor techniques is described. The analog portion of the circuit consists of two operational amplifiers, four capacitors, and ten switches regardless of the number of bits per sample converted, and completes an n-bit conversion in 3n clock cycles. The conversion characteristics are inherently insensitive both to capacitor ratio and to amplifier offset voltage. The circuit, therefore, can be realized in a small die area. The effects of finite amplifier gain and switch charge injection on the conversion accuracy are discussed. A prototype chip has been fabricated in a 2- mu m CMOS technology operating on a single 5-V supply. When it is operated as an 8-bit converter at a sampling rate of 8 kHz, the maximum conversion error is 0.2 LSB (least-significant bit) for differential nonlinearity and 0.5 LSB for integral nonlinearity. The die area measures 0.79 mm/sup 2/.<
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