SBOA293A December 2018 – January 2021 TLV9002

**Design Goals**

Input | Output | BW | Supply | |||
---|---|---|---|---|---|---|

V_{iMin} | V_{iMax} | V_{oMin} | V_{oMax} | f_{p} | V_{ee} | V_{cc} |

–0.1V | 0.1V | –2V | 2V | 2kHz | –2.5V | 2.5V |

**Design Description**

This tunable low–pass inverting amplifier circuit amplifies the signal level by 26dB or 20V/V. R_{2} and C_{1} set the cutoff frequency for this circuit. The frequency response of this circuit is the same as that of a passive RC filter, except that the output is amplified by the pass–band gain of the amplifier. Low–pass filters are often used in audio signal chains and are sometimes called bass–boost filters.

**Design Notes**

- C
_{1}and R_{2}set the low–pass filter cutoff frequency. - The common-mode voltage is set by the non–inverting input of the op amp, which in this case is mid–supply.
- Using high value resistors can degrade the phase margin of the circuit and introduce additional noise in the circuit.
- R
_{2}and R_{1}set the gain of the circuit. - The pole frequency f
_{p}of 2kHz is selected for an audio bass–boost application. - Avoid placing capacitive loads directly on the output of the amplifier to minimize stability issues.
- Large signal performance may be limited by slew rate. Therefore, check the maximum output swing versus frequency plot in the data sheet to minimize slew–induced distortion.
- For more information on op amp linear operation region, stability, slew–induced distortion, capacitive load drive, driving ADCs and bandwidth please see the design references section.

**Design Steps**

The DC transfer function of this circuit is given below.

Equation 1.

- Pick resistor values for given passband gain. Equation 1.Equation 1.Equation 1.
- Select low–pass filter pole frequency f
_{p}Equation 1. - Calculate C
_{1}using R_{2}to set the location of f_{p}.Equation 1.Equation 1. - Calculate the minimum slew rate required to minimize slew–induced distortion. Equation 1.Equation 1.
- SR
_{TLV9002}= 2V/µs, therefore it meets this requirement

**Design Simulations**

**AC Simulation Results**

**Transient Simulation Results**

A 100 Hz, 0.2 V_{pp} sine wave yields a 4 V_{pp} output sine wave.

A 100 kHz, 0.2 V_{pp} sine wave yields a 0.1 V_{pp} output sine wave.

**References:**

- Analog Engineer's Circuit Cookbooks
- SPICE Simulation File SBOC523
- TI Precision Designs TIPD185
- TI Precision Labs

**Design Featured Op Amp**

TLV9002 | |
---|---|

V_{ss} | 1.8V to 5.5V |

V_{inCM} | Rail–to–rail |

V_{out} | Rail–to–rail |

V_{os} | 0.4mV |

I_{q} | 60µA |

I_{b} | 5pA |

UGBW | 1MHz |

SR | 2V/µs |

#Channels | 1,2,4 |

www.ti.com/product/tlv9002 |

**Design Alternate Op Amp**

OPA375 | |
---|---|

V_{ss} | 2.25V to 5.5V |

V_{inCM} | V_{ee} to V_{cc} –1.2V |

V_{out} | Rail–to–rail |

V_{os} | 0.15mV |

I_{q} | 890µA |

I_{b} | 10pA |

UGBW | 10MHz |

SR | 4.75V/µs |

#Channels | 1 |

www.ti.com/product/opa375 |

Revision | Date | Change |
---|---|---|

A | January 2021 | Updated result in Design Step 4 from 0.25 to 0.025 |