A 630μW zero-crossing-based ΔΣ ADC using switched-resistor current sources in 45nm CMOS

A delta-sigma analog-to-digital converter employs zero-crossing-based integrators to achieve low power operation at 50MHz sampling rate. Switched resistors, used as current sources, provide good dynamic current matching, eliminating the need for common-mode feedback circuits. The effect of the switched resistors on the linearity of the zero-crossing-based integrator is discussed. Also, a unidirectional 2-phase charging scheme is proposed to improve input signal swing and reduce overshoot voltage. Test chip implemented in a 45nm LP Digital CMOS achieves 54.3dB DR, 52.5dB SNR, and 47.7dB SNDR at 0.833MHz input while dissipating 630μ;W from a 1.1V supply.

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