As shown in the figure. The noninverting AC amplifier is characterized by high input impedance. Among them, R 1 and R2 form a 1/2V+ voltage divider circuit, and the operational amplifier is biased by R3. The voltage amplification factor Av of the circuit is only determined by the external resistance: Av= 1+Rf/R4, and the input resistance of the circuit is R3. The resistance of R4 varies from several thousand ohms to tens of thousands of ohms.

2. Introduction to 2.LM324N

LM324 is a four-op-amp integrated circuit, which is packaged in 14-pin dual in-line plastic package, and its shape is shown in the figure. It contains four groups of identical operational amplifiers, which are independent of each other except the power supply. Each group of operational amplifiers can be represented by the symbol shown in figure 1 It has five pins, of which "+"and "-"are two signal inputs, "V+" and "V-" are positive and negative power supplies, and "Vo" is the output. Of the two signal input terminals, Vi-(-) is the inverting input terminal, and the signal representing the output terminal Vo of the operational amplifier is opposite to the bit of the input terminal; Vi+(+) is the noninverting input terminal, and the signal representing the output terminal Vo of the operational amplifier is in the same phase as the input terminal. See figure for the pin arrangement of LM324: