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 45mn LP Digital CMOS achieves 543dB DR, 525dB SNR, and 47.7dB SNDR at 0.833MHz input while dissipating 630 mu W from a 1.1V supply.