Low Noise Operational Amplifier Using Dual-Path Dual-Chopper Fill-In Technique

A low noise operational amplifier is the key building block of the high precision sensor interface circuit. The conventional continuous-time operational amplifiers suffer from the low frequency noise components, and the multipath amplifiers are good solution to achieve both the low noise and wide bandwidth. This paper presents a low noise multipath chopper-stabilized operational amplifier with dual-path dual-chopper fill-in technique. The low-frequency path of the multipath amplifier is implemented using two dual-path chopper amplifiers. The noise correlation between the dual path chopper amplifiers can reduce the input referred noise level. The dual chopper amplifiers are driven by two quadrature chopper clocks. The glitch-free durations of the chopper amplifier outputs are combined using fill-in technique to reduce the unwanted switching artifacts including glitches and intermodulation distortions (IMDs). The circuit was fabricated using a 180 nm complementary metal-oxide-semiconductor (CMOS) process and draws 46.5 μA at a supply voltage of 1.8V. The input referred noise and input-referred offset are 6.42 nV/√Hz and 10.5 μV, respectively. The gain-bandwidth product is 874 kHz. The power supply rejection ratios (PSRR+ and PSRR-) and common mode rejection ratio (CMRR) are 118 dB, 111 dB and 90 dB, respectively. The chopper clock is 19 kHz. The IMD tones with 75 kHz is input are below -61 dB.