3.3 A Passive Switched-Capacitor-Based Multimode Amplifier with a Logarithmic Conformity Error of 0.75% from -25 to 200°C

Harnessing new renewable energy sources, such as geothermal energy, requires integrated electronics to endure harsh environments with temperatures up to 200°C. Acoustic sensors (e.g., piezoelectric) detect environmental composition, as illustrated in Fig. 3.3.1 (top). Due to the natural wide amplitude range of sound pressure waves (1-to-20kHz), the amplifiers in the sensor front-end need both a wide dynamic range (DR) > 80dB to maintain a reasonable signal-to-noise ratio (SNR) at the ADC input, as well as accurate phase and amplitude measurement across a wide temperature range. While logarithmic amplifiers [1], [2], dB-linear amplifiers [3], or automatic gain control (AGC) [4] achieve a high DR, they require post-processing to restore true amplitude levels. Furthermore, logarithmic amplifiers exhibit considerable temperature dependence. Low-drift amplifiers [5] with a typical gain drift of 0.7 ppm/°C can be used over a wide temperature range, but their precision requires trimmed ratios and temperature compensation, leading to complex circuits with reduced reliability at high temperatures. Stacked constant-time amplifiers [6] can be used to achieve high noise efficiency, but advanced discrete-time amplifiers can achieve even higher efficiencies [7]. However, the drawbacks of aliasing and noise folding have to be addressed.