Time-Domain Operational Amplifier With Voltage-Controlled Oscillator and Its Application to Active-RC Analog Filter

Time-domain operational amplifier (op-amp) is developed with only time-domain circuits such as voltage-controlled oscillator (VCO) and voltage-controlled delay line (VCDL). The infinite dc-gain of the voltage-to-phase transfer characteristic of VCO allows the time-domain op-amp to have large dc-gain. The frequency compensation is performed by the left-half plane (LHP) zero created by VCDL whose output phase is proportional to its control input voltage. With the proposed time-domain op-amp, a fourth-order continuous-time (CT) analog filter with 25 MHz cut-off frequency has been implemented in a 65 nm CMOS technology. The filter occupies 0.107 mm
²
and operates with 0.9 V supply consuming 8.2 mW. The measured in-band input third-order intercept point (IIP3) is 22.6 dBm and the peak signal-to-noise+distortion ratio (SNDR) is 60.9 dB.