This paper reports on an energy-efficient \Delta -\Sigma readout IC (ROIC) with a high power-supply-rejection ratio (PSRR). The static power consumption is minimized by applying a zero-crossing-based (ZCB) circuit to implement switched-capacitor (SC) integrators, while the resistive sensor is embedded inside the circuit to reuse the bias current. Oversampling \Delta -\Sigma modulation also directly provides the digitized output, avoiding the need for a power-hungry instrumentation amplifier while preserving the linear settling behavior of the ZCB SC integrators. A dual-path bridge measurement AIDS in upholding PSRR of ROIC against bridge imbalance. Prototyped in 0.18-\mu \text{m} CMOS, the dual-path ROIC for the bridge measurement shows a nonlinearity of <400 ppm and an rms-noise-equivalent resolution of 13 bits at a conversion rate of 8 kS/s, corresponding to a figure of merit of 1.05-pJ/conversion step. The achieved noise-frequency-independent PSRR is 65 dB, and the supply and temperature sensitivities are 0.23%/V and 55 ppm/°C, respectively.