Design Description

This circuit is a 2nd-order multiple feedback (MFB) band-pass (BP) filter. This BP filter is created by cascading a low-pass and a high-pass filter. V_ref provides a DC offset to accommodate for single-supply applications.

Design Notes

1. Select an op amp with sufficient input common-mode range and output voltage swing.
2. Add V_ref to bias the input signal to meet the input common-mode range and output voltage swing.
3. Select the capacitor values first since standard capacitor values are more coarsely subdivided than the resistor values. Use high-precision, low-drift capacitor values to avoid errors in f_l and f_h.
4. To minimize the amount of slew-induced distortion, select an op amp with sufficient slew rate (SR).
5. For HP filters the maximum frequency is set by the gain bandwidth (GBW) of the op amp. Therefore, be sure to select an op amp with sufficient GBW.

Design Steps

This BP filter design involves two cascaded filters, a low-pass (LP) filter and a high-pass (HP) filter. The lower cutoff frequency (f_l) of the BP filter is 1kHz and the higher cutoff frequency (f_h) is 10kHz. The design steps show an LP filter design with f_h of 10kHz and a HP filter design with f_l of 1kHz. See MFB low-pass filter design and MFB high-pass filter design in the circuit cookbook for details on transfer function equations and calculations.

LP Filter Design

1. Use MFB low-pass filter design to determine R₁, R₂, and R₃.
   ${\text{R}}_1\text{= 10kΩ, }{\text{R}}_2\text{= 10kΩ, }{\text{R}}_3\text{= 10kΩ }$
2. Use MFB low-pass filter design to determine C₁ and C₂.
   ${\text{C}}_1\text{= 3.3nF (Standard Value),}{\text{C}}_2\text{= 750pF (Standard Value)}$

HP Filter Design

1. Use MFB high-pass filter design to determine C₄, C₅, and C₆.
   ${\text{C}}_4\text{= 1nF,}{\text{C}}_5\text{= 1nF,}{\text{C}}_6\text{= 1nF }$
2. Use MFB high-pass filter design to determine R₄ and R₅.

Design Simulations

AC Simulation Results

Transient Simulation Results

Filter Ouput in Response to a 5-Vpp, 100-Hz Input Signal (Gain = 0.01V/V)

Filter Ouput in Response to a 5-Vpp, 5-kHz Input Signal (Gain = 1V/V)

Filter Ouput in Response to a 5-Vpp, 100-kHz Input Signal (Gain = 0.01V/V)

Design References

1. See Analog Engineer's Circuit Cookbooks for TI's comprehensive circuit library.
2. SPICE Simulation File: SBOC596.
3. TI Precision Labs.

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