How to Choose R2 and Cinf for Av=1500 in LTSpice Amplifier Simulation (Vcc=10V, R1=15k)

The discussion focuses on selecting appropriate values for resistor R2 and capacitor Cinf in an LTSpice amplifier simulation to achieve a theoretical voltage gain (Av) of 1500, with constraints including Vcc=10V, VCM=1.5V, input sine wave frequency of 1 kHz, and R1=15 kΩ. Guidance includes performing parametric sweeps of R2 and Cinf to map gain variations and using regression to derive a formula for gain prediction. Gain measurement is clarified as the ratio of output to input voltage (Vout/Vin), typically expressed in dB as 20·log(Av), with emphasis on measuring peak-to-peak voltages at appropriate nodes, considering DC offsets and signal referencing relative to ground. To minimize output distortion, input amplitude should be chosen carefully, with suggestions to analyze distortion via FFT or harmonic distortion analysis using the ".four" directive in LTSpice. A method to reduce gain without altering R1, R2, Vcc, or VCM involves adding a feedback loop similar to operational amplifier configurations: setting R2 to 10 kΩ for ~1 mA current sources, adjusting VCM to 5 V, inserting a 1 kΩ resistor in series with the inverting input base, adding a 1.499 MΩ resistor for feedback, and using a 100 pF capacitor to prevent oscillations. Cinf is recommended at 10 µF to ensure low reactance compared to R1. The amplifier is powered between Vcc and ground, not symmetric rails, and output saturation and DC offset effects are noted when increasing input amplitude. Simulation techniques include transient and AC sweep analyses, with cursor measurements for voltage levels to calculate gain accurately.
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