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 50 MHz 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 45 nm LP digital CMOS achieves 54.3 dB DR, 52.5 dB SNR, and 47.7 dB SNDR at 0.833 MHz input while dissipating 630 muW from a 1.1 V supply.