Adjustment principle of electronic potentiometer

16. From the structure of an electronic potentiometer composed of digital integrated circuits, we know that the basic working principle of an electronic potentiometer is to control the amount of resistance in the attenuation resistor network
through an analog switch , thereby adjusting the attenuation of the input signal. To achieve the purpose of controlling
the volume. As shown in Figure 4-16 (a), when the switch Ki (equivalent to an electronic analog switch) is closed and the other switches are open,
there is a short circuit between the input and the output, and the signal is output directly without attenuation; if Kz is closed, the other switches are open When ,
the relationship between output and input is: Vo (Ri+R2+R3+R4)=Vi (R2+R3+R4); similarly, if the remaining switches
are closed , the output signal will follow the above relationship. Attenuation is achieved according to the ratio of the resistor network, that is, when K3 is closed
: Vo (only i+RZ+R3 +R4)=Vj (R3+R4), etc. Obviously, in order to obtain the maximum attenuation and at the same time
have high enough resolution accuracy, it is necessary to have enough resistance levels and corresponding electronic switches. For example, to
form a two-channel electronic potentiometer with a maximum attenuation of 80dB and a resolution of 2dB, 76 analog switches are needed
. This is obviously not suitable for production using digital integrated circuits. Modern integrated circuit manufacturing technology can completely
integrate these functions into one circuit to become an electronic potentiometer
circuit with complete functions of adjustment, counting, selection switch and resistor network .     In practical application circuits, in order to obtain the required attenuation characteristics and sufficient resolution the minimum number of analog switches and resistors, a two-stage attenuation method is adopted. The first attenuation is 5 to 10dB, and the second is The second level uses an attenuation of 1 to 2dB. The structural principle is shown in Figure 4-16 (b).