SBOA294 April 2021 OPA375 , TLV9001

**Design Goals**

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

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

–0.1V | 0.1V | –2V | 2V | 10kHz | 2.5V | –2.5V |

**Design Description**

This low-pass non-inverting circuit amplifies the signal level by 20V/V (26dB) and filters the signal by setting the pole at 10kHz. Components R_{1} and C_{1} create a low-pass filter on the non-inverting pin. 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. Components C_{2} and R_{3} are used to set the cutoff frequency, f_{c,} of the non-inverting amplifier.

**Design Notes**

- The common-mode voltage is equal to the input voltage applied to the non-inverting input of the op amp.
- Using high-value resistors can degrade the phase margin of the circuit and introduce additional noise in the circuit.
- Set the pole frequency created by R
_{3}/ C_{2}to be ten times higher than the pole created by R_{1}/ C_{1}to achieve a single poll roll-off that is dominated by R_{1}/ C_{1}. If the filter pairs R_{1}/ C_{1}and R_{3}/ C_{2}have the same pole frequency, the gain will be reduced by 6dB at the cutoff frequency. Also the gain decreases at a rate of –40dB/dec until the response reaches 0dB, after which the slope changes to –20dB/dec until the op amp runs out of bandwidth. - C
_{2}limits the bandwidth of the non-inverting gain stage. - 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 an op amp linear operating region, stability, slew-induced distortion, capacitive load drive, driving ADCs, and bandwidth, see the
*Design References*section.

**Design Steps**

The DC transfer function of this circuit follows:

Equation 1. ${\text{V}}_{o}{\text{= V}}_{\text{in}}\text{\xd7}\left(\text{1 +}\frac{{\text{R}}_{\text{3}}}{{\text{R}}_{\text{2}}}\right)$

- Calculate the gain. Equation 1. $\text{Gain=}\frac{{\text{V}}_{\text{oMax}}{\text{\u2013V}}_{\text{oMin}}}{{\text{V}}_{\text{iMax}}{\text{\u2013V}}_{\text{iMin}}}\text{=}\frac{\text{2V\u2013(\u20132V)}}{\text{0.1V\u2013(\u20130.1V)}}\text{=20}\frac{\text{V}}{\text{V}}$
- Calculate values for R
_{2}and R_{3}.Equation 1. $\text{Gain =1 +}\frac{{\text{R}}_{\text{3}}}{{\text{R}}_{\text{2}}}\text{= 20}\frac{\text{V}}{\text{V}}\text{\u2192}\text{(26dB)}$Choose R

_{2}= 1kΩ:Equation 1. ${\text{R}}_{3}{\text{= (Gain \u2013 1) \xd7 R}}_{2}\text{= 19k\u2126}$ - Calculate the component values R
_{1}and C_{1}to set the cutoff frequency, f_{c}. Pick the value of R_{1}and then calculate C_{1}to set the location of f_{c}.Choose R

_{1}= 1kΩ:Equation 1. ${\text{C}}_{1}\text{=}\frac{\text{1}}{{\text{2\pi \xd7 R}}_{1}{\text{\xd7 f}}_{c}}\text{=}\frac{\text{1}}{\text{2\pi \xd7 1k\u2126 \xd7 10kHz}}\text{= 15.92nF\u2248 16nF(StandardValue)}$ - Calculate C
_{2}value to set the cutoff frequency (f_{c}) of the op amp. Select the corner frequency to be at least ten times larger than f_{c}.Equation 1. ${f}_{c}{\text{=10kHz;10 \xd7 f}}_{c}\text{= 100kHz}$Equation 1. ${\text{C}}_{2}\text{=}\frac{\text{1}}{{\text{2\pi \xd7 R}}_{3}\text{\xd7}\mathrm{100kHz}}=\frac{\text{1}}{\text{2\pi \xd7 19k\u2126 \xd7 100kHz}}\text{= 83.77pF\u224882pF(StandardValue)}$

**Design Simulations**

**AC Simulation Results**

**Transient Simulation Results**

A 1-kHz, 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 0.071-V_{PP} output sine wave.

**Design References**

- See Analog Engineer's Circuit Cookbooks for the comprehensive TI circuit library.
- SPICE Simulation File SBOC528.
*TI Precision Labs*- See the
*AC Coupled, Single-Supply, Inverting and Non-inverting Amplifier Reference Design*.

**Design Featured Op Amp**

TLV9001 | |
---|---|

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/TLV9001 |

**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 | 1,2,4 |

www.ti.com/product/OPA375 |