SBOA296 April 2021 OPA322 , OPA350 , TLV9062

**Design Goals**

Input | Output | Frequency | Supply | |
---|---|---|---|---|

V_{iMax} | V_{oMax} | f | V_{cc} | V_{ee} |

9Vpp | 4.5Vpp | 50kHz | 5V | 0V |

**Design Description**

This single-supply precision full-wave rectifier is optimized for high-input voltages. When V_{i} > 0V, D_{1} 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, D_{1} 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**

- Observe common-mode and output swing limitations of op amps.
- R
_{3}should be sized small enough that the leakage current from D_{1}does not cause errors for positive input cycles while ensuring the op amp can drive the load. - Use a fast switching diode for D
_{1}. - Resistor tolerance determines the gain error of the circuit.
- 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*. - 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**

- Circuit analysis for positive input signals. D
_{1}is reverse-biased disconnecting the output of U_{2}from the non-inverting input of U_{1}.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. ${V}_{o}={V}_{i}$ - Circuit analysis for negative input signals. D
_{1}is forward biased, which connects the output of U_{2}to the non-inverting input of U_{1}, which is GND.Equation 1. $\frac{{V}_{o}}{{V}_{i}}=\left(-\frac{{R}_{2}}{{R}_{1}}\right)=-1$Equation 1. ${V}_{o}=-{V}_{i}$ - Select R
_{1}, R_{2}, and R_{3}.Equation 1. $\frac{{V}_{o}}{{V}_{i}}=-\frac{{R}_{2}}{{R}_{1}}$

Equation 1. $\text{If}{R}_{2}={R}_{1}\text{then}{V}_{o}=\u2013{V}_{i}$

Equation 1. $\text{Set}{R}_{1}={R}_{2}={R}_{3}=\mathrm{1k\Omega}$

**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**

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

**Design Featured Op Amp**

TLV9062 | |
---|---|

V_{ss} | 1.8V to 5.5V |

V_{inCM} | Rail–to–rail |

V_{out} | Rail–to–rail |

V_{os} | 0.30mV |

I_{q} | 538µA |

I_{b} | 0.5pA |

UGBW | 10MHz |

SR | 6.5V/µs |

#Channels | 1, 2, 4 |

www.ti.com/product/TLV9062 |

**Design Alternate Op Amps**

OPA322 | OPA350 | |
---|---|---|

V_{ss} | 1.8V to 5.5V | 2.7V to 5.5V |

V_{inCM} | Rail–to–rail | Rail–to–rail |

V_{out} | Rail–to–rail | Rail–to–rail |

V_{os} | 2mV | 0.15mV |

I_{q} | 1.9mA | 5.2mA |

I_{b} | 10pA | 0.5pA |

UGBW | 20MHz | 38MHz |

SR | 10V/µs | 22V/µs |

#Channels | 1, 2, 4 | 1, 2, 4 |

www.ti.com/product/OPA322 | www.ti.com/product/OPA350 |