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. Conventional continuous-time operational amplifiers suffer from low-frequency noise components, and multipath amplifiers are a good solution to achieve both low-noise and wide bandwidth. This article presents a low-noise multipath chopper-stabilized operational amplifier with a dual-path dual-chopper fill-in technique. The low-frequency path (LFP) 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 the 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 <tex-math notation="LaTeX">46.5 ~μ A </tex-math> at a supply voltage of 1.8 V. The input-referred noise and input-referred offset are 6.42 nV/ <tex-math notation="LaTeX"> </tex-math> Hz and <tex-math notation="LaTeX">10.5 ~μ V </tex-math> , respectively. The gain-bandwidth product is 874 kHz. The power supply rejection ratios (PSRR+ and PSRR−) and common mode rejection ratio (CMRR) are 118, 111, and 90 dB, respectively. The chopper clock is 19 kHz. The IMD tones with 75 kHz input are below −61 dB.