An area-efficient voltage-controlled oscillator (VCO) based Hall sensor readout system for autofocus applications is reported in this paper. The proposed chip consists of an on-chip Hall-effect sensor and a readout circuit. In the readout circuit, the frontend amplifier is embedded in a VCO-based readout circuit for area-efficient realization. The VCO is implemented as a Gm stage followed by a current-controlled oscillator (Gm-CCO). The chopper technique is applied to suppress the flicker noise. In contrast to prior work, this work adopts a digital demodulation (de-chopper) that mitigates the residual offset from the mismatch of two CCOs. Furthermore, digital offset reduction loop (DORL) is proposed to alleviate the dynamic range limitation due to Hall sensor offset. The complete system is fabricated in the TSMC 180-nm CMOS process; the core area is 0.25 mm 2 . With a 2.5-kHz bandwidth, the SNR is 51 dB under a 150-mT magnetic field input. The circuit power consumption is 191 μW.