A 0.5-V 1-μW successive approximation ADC

A successive approximation analog-to-digital converter (ADC) is presented operating at ultralow supply voltages. The circuit is realized in a 0.18-mum standard CMOS technology. Neither low-V-T devices nor voltage boosting techniques are used. All voltage levels are between supply voltage V-DD and ground V-SS. A passive sample-and-hold stage and a capacitor-based digital-to-analog converter are used to avoid application of operational amplifiers, since opamp operation requires higher values for the lowest possible supply voltage. The ADC has signal-to-noise-and-distortion ratios of 51.2 and 43.3 dB for supply voltages of 1 and 0.5 V, at sampling rates of 150 and 4.1 kS/s and power consumptions of 30 and 0.85 muW, respectively. Proper operation is achieved down to a supply voltage of 0.4 V.