A 1.8-GΩ Input Impedance 45-dB Ripple Reduction Factor Chopper Amplifier for Biomedical Recording

The chopping technique is widely used in biomedical amplifiers to create a biomedical chopper amplifier (BiCA) which achieves high noise efficiency. However, this approach brings some critical disadvantages to BiCA, such as: (1) output ripple appearance; (2) input impedance reduction. In this paper, the proposed BiCA with high input impedance, low power and noise for biomedical recording applications is presented. A chopper ripple rejection loop (CRRL) is proposed to achieve low output ripple. An impedance boosting loop (IBL) is added to boost the input impedance of the BiCA from $2.5 {\mathrm {M}} \Omega$ to 1.8 G$\Omega$. The BiCA simulated in a 0.18$-\mu$m CMOS process occupies only 0.123 $\mathrm{mm}^{2}$ and has a power consumption of 1.87 μW at 1 V supply. The ripple attenuation factor of about 45 dB is achieved when CRRL is enabled. When both CRRL and IBL are enabled, the input referred noise of the proposed BiCA is 1.81 $\mu V_{\mathrm{r}\mathrm{m}\mathrm{s}}$. Therefore, the proposed BiCA is an effective approach for recording biomedical signals.