Precision Full Wave Rectifier:

The Precision Full Wave Rectifier circuits accept an ac signal at the input, inverts either the negative or the positive half, and delivers both the inverted and noninverted halves at the output, as shown in the Fig. 2.62.

The operation of the positive full wave rectifier is expressed as

and that of the negative rectifier as

Looking at equations 1 and 2 we can say that Precision Full Wave Rectifier circuits are precision absolute value circuits. Fig. 2.63 shows a full wave rectifier or absolute value circuit.

CASE 1 : V_i > 0 : When V_i > 0, inverting side of A₁ will force its output to swing negative, thus forward biasing D₁ and reverse biasing D₂. Since no current flows through resistance R connected between V_n1 and V_p2, both are equipotential

The Fig. 2.64 shows the equivalent circuit.

From equivalent circuit, the output voltage can be given

CASE 2 : V_i < 0 : When V_i < 0, negative, the output voltage of A₁ swings to positive, making diode D₁ reverse biased and diode D₂ forward biased.

The Fig. 2.65 shows the equivalent circuit.

Let the output voltage of op-amp A₁ be V. Since the differential input to A₂ is zero, the inverting input terminal is also at voltage V, as shown in the Fig. 2.65.

Applying KCL at node ‘a’ we have

To find V_o in terms of V we concentrate on the equivalent circuit of A₂, as shown in the Fig. 2.66.

Substituting value of V in above equation we get,

Hence for V_i < 0 the output is positive. This is illustrated in Fig. 2.67.