2) Precision Full-Wave Rectifiers (Absolute Value Circuit) 2.1) Half-Wave Rectifier and Summing Circuit
The left side of the circuit in Fig.7-4 is a precision half wave rectifier as in Fig.7-2 but with the diodes reversed.
The right side is an inverting summing amplifier circuit.
The input voltage is applied to terminal A of the summing amplifier and to the input of the precision rectifier.
Note that resistors R2 in the precision half-wave rectifier circuit has twice the resistance of R1, so the rectified voltage applied to terminal B of the summing amplifier is -2 Vi, as illustrated.