Increasing Input Impedance Circuit

Published:2011/6/21 19:41:00 Author:Robert | Keyword: Increasing, Input, Impedance | From:SeekIC

The picture shows the circuit which increases the input impedance by adding front amplifier stage. Those amplifier circuit, which used in small current amplification or large signal internal resistance case, needs very high input impedance. Some could be more than 1x1012Ω. To increase the input impedance, the most direct way is to use the input stage composed of FET and add it in parallel before the amplifier. The circuit in the picture can make the VT2 static working point stable. R1, R2 and RP1 is used to get the balance of the output voltage of the front amplifier stage.



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