A CMOS frequency-mixing transimpedance amplifier with 5nArms input noise for frequency-domain near-infrared spectroscopy

A novel frequency mixing transimpedance amplifier (FM-TIA) is proposed and implemented in 0.18μm CMOS for low-noise detection of sinusoidally-modulated optical signals in frequency-domain near infrared (NIR) spectroscopy instrumentation. The FM-TIA topology employs a T-feedback resistor network incorporating gate-controlled transistors for resistance modulation, enabling operation in both wideband and frequency-mixing mode. In wideband mode, the TIA achieves a transimpedance gain of 110 dBΩ, 263 MHz bandwidth, 230 nA_rms total integrated input current noise and 1 dB compression point of 1.65 μA for 4pF photodiode capacitance. In frequency-mixing mode, the amplifier is capable of directly downconverting and amplifying photocurrent signals generated by near-infrared excitation light modulated at 100 MHz. The FM-TIA obtains 5 nA_rms input noise, current-to-voltage conversion gain of 93 dBQ, and 1 dB compression point of 1.1 μA with up to 47 dB dynamic range. The amplifier consumes only 22 mW of power from a 1.8 V supply.