This paper proposes a time-domain AC bridge for impedance spectroscopy. In the proposed system, the AC signal source consists of switches and a digital ΔΣ modulator, and an oscillator and a counter are used to detect the voltage error for least-mean-square algorithm for auto-balancing. Due to the noise shaping of the ΔΣ DAC and the low-pass filter characteristics of the VCO, it is possible to read the impedance without an amplifier. The developed prototype of the proposed system achieved precise complex-impedance measurement from 50 Hz to 10 kHz input signal within 0.33% accuracy.