Low-Pass, Filtered, Inverting Amplifier Circuit

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. R₂ and C₁ 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

C₁ and R₂ 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.
R₂ and R₁ 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 C₁ using R₂ 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 History

Revision	Date	Change
A	January 2021	Updated result in Design Step 4 from 0.25 to 0.025

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