Design Goals

Design Description

This single-supply precision full-wave rectifier is optimized for high-input voltages. When V_i > 0V, D₁ is reverse biased and the top part of the circuit, U1, is activated resulting in a circuit with a gain of 1V/V. When Vi < 0V, D₁ is forward biased and the bottom part of the circuit, U2, is activated resulting in an inverting amplifier circuit with a gain of –1V/V.

Design Notes

1. Observe common-mode and output swing limitations of op amps.
2. R₃ should be sized small enough that the leakage current from D₁ does not cause errors for positive input cycles while ensuring the op amp can drive the load.
3. Use a fast switching diode for D₁.
4. Resistor tolerance determines the gain error of the circuit.
5. Use a negative charge pump (such as the LM7705) for output swing requirements to GND to maintain linearity for output signals near 0V. For additional information. see Single-supply, low-input voltage, full-wave rectifier circuit.
6. For more information on op amp linear operating region, stability, capacitive load drive, driving ADCs, and bandwidth please see the Design References section.

Design Steps

1. Circuit analysis for positive input signals. D₁ is reverse-biased disconnecting the output of U₂ from the non-inverting input of U₁.
   
   Equation 1. $\frac{V_o}{V_i}=\left(-\frac{R_2}{R_1}\right)+\left(1+\frac{R_2}{R_1}\right)=1$
   Equation 1. $V_o=V_i$
2. Circuit analysis for negative input signals. D₁ is forward biased, which connects the output of U₂ to the non-inverting input of U₁, which is GND.
   
   Equation 1. $\frac{V_o}{V_i}=\left(-\frac{R_2}{R_1}\right)=-1$
   Equation 1. $V_o=-V_i$
3. Select R₁, R₂, and R₃.
   Equation 1. $\frac{V_o}{V_i}=-\frac{R_2}{R_1}$

Design Simulations

Transient Simulation Results

A 1-kHz, 9-V_pp sine wave yields a 4.5-V_pp output sine wave.

A 50-kHz, 9-V_pp sine wave yields a 4.5-V_pp output sine wave.

Design References

1. See Analog Engineer's Circuit Cookbooks for the comprehensive TI circuit library.
2. SPICE Simulation File SBOC529.
3. TI Precision Labs
4. See the Single-Supply Low-Input Voltage Optimized Precision Full-Wave Rectifier Reference Design.

Design Featured Op Amp

Design Alternate Op Amps