Variable gain preamplifier circuit

The task of the preamplifier is to amplify the small analog input signal to within the range of the A/D conversion (such as 0-5VDC). In order to adapt to the
amplification needs of a variety of small signals, a variable gain amplifier is designed, as shown in Figure 2718 shown. 1
    This figure uses two methods of selecting the gain. One is to select the gain of the human-level amplifier through switches S1-S4, and the gains are 2, 3, 5, and 9 respectively
; the other is to give the control word (DO) through the program. ~D2) Select the digital input terminals DI11~DI4 of the D/A converter DAC1210, whose gain is divided into
    16. The numbers
are 2, 4, 8, 16, 32, 64, 128, and 256.
    In the figure, the arithmetic circuits A1, A2 and A3 are non-inverting f-input amplifiers, and the amplifier gain K=l+R≮R, where R is
R1 respectively. ,jk,Rl. R1. , if there is only one resistor in the switches S1-S4 as the input resistor R, then the gains of the amplifier are 2, 3, 5, and 9 respectively.
    The D/A converter has changed its wiring method and been connected to an amplifier. As long as the control word is given through the program to change the state of the data input terminal
, the amplifier gain can be changed. In the figure, the data lines EIo, D1 and D2 are used to control the
8 data input terminals Dll1~Dl4 of the nAC1210 through the g outputs of the 3-8 line decoder. The corresponding amplification gains are equivalent to 2, 4, 8,... ,256.