This circuit, shown in the figure, consists of a variable gain amplifier with differential input for instrumentation applications. The gain is given by the value of R6 and the other resistors must be accurate, as indicated in the diagram itself. The power supply must be symmetrical. Note that the use of the LM102, voltage follower, at the input of the circuit guarantees a very high input resistance (10 000M ohms), thus isolating the input of the amplifier step itself. Among the possible applications for this circuit are biological amplifiers (polygraphs, etc.) and devices with very high impedance transducers.
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