Wide dynamic range multichannel lock-in amplifier for contactless optical sensors with sub-pS resolution

A multichannel impedance-sensing CMOS chip for the readout of noninvasive light detectors in silicon photonics (SiP) is presented. The performance of the lock-in phase-sensitive demodulator is improved thanks to a capacitive feedback transimpedance amplifier (TIA) equipped with an active discharge network, able to keep a dc output offset lower than 3 mV for leakage currents up to 4 nA while injecting a noise lower than 40 fA/ $\sqrt {\mathrm{ Hz}}$ . The addition of a sensor capacitance compensation system at the input of the chip allows a 30-fold increase of the stimulation amplitude, enabling the tracking of sub-picoSiemens conductance variations on a baseline of few $\mu \text{S}$ , with a bandwidth of 70 Hz. The chip performance opens the way to multipoint monitoring of complex photonic systems, addressing the challenges posed by the growing complexity of these architectures.