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The input resistance of an AC-coupled op amp circuit depends almost entirely on the DC dissipation resistance. settings are defined. When using CMOS op amps, the input resistance is usually high, currently up to 10MΩ. If you want higher values, you can use a starter circuit. This allows the input resistance to be artificially increased to very high values. In fact, in the circuit shown, resistor R1 regulates the DC current. IC1a score. The terminal of the resistor connected to pin 7 of IC1 is normally at ground potential, so the input impedance is 10MΩ.
Connect the other resistor terminal to ground through IC1a and connect C2-R3-R2 to DC. DC drive related. inquiry. Install the op amp. For AC voltage, only a small amount of AC current flows through R1 as the input signal is fed back. So phosphorus = R1[(R2+R3)/R3]. With the specified resistor values, Rin is approximately 1 GΩ. One aspect to note: (R2+R3)/R3 should not exceed 0.99. This means that if the value of R2 is 10MΩ, the value of R3 cannot be less than 100kΩ. If these conditions are not met, the circuit will be unstable.