Band Pass Filters

## Active Band-Pass Filter (BPF)

A band-pass filter (BPF) passes frequencies within a certain range and rejects (attenuates) frequencies outside that range. It can be made by combining the first order low pass and high pass filter. The picture below shows an example of an active BPF.

Intermediate pass frequencies fC2 < f < fC1 with a gain of -R1/R2 where fC1 = 1/(2 pi R1 C1), fC2 = 1/(2 pi R2 C2).

The bode plot of the active BPF is shown below. fPL= fpass-lower = fC2= 1/(2 pi R2 C2), fPU = fpass-upper= fC1= 1/(2 pi R1 C1)

Design Example
Design an active BPF that allows frequencies between 1.6 kHz and 16 kHz to pass through with a gain of -20.

Solution
fPL =1/(2 pi R2 C2) = 1.6 kHz, C2 = 1 μF, R2 ≈ 100 Ω
Passing intermediate frequencies with a gain of -10, i.e., R1/R2 = 10, R1 = 10 X R2 = 1 kΩ
fPU = 1/(2 pi R1 C1) = 16kHz, C1= 0.01 μF

© 2024 Microchip Technology, Inc.
Notice: ARM and Cortex are the registered trademarks of ARM Limited in the EU and other countries.
Information contained on this site regarding device applications and the like is provided only for your convenience and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. MICROCHIP MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED, WRITTEN OR ORAL, STATUTORY OR OTHERWISE, RELATED TO THE INFORMATION, INCLUDING BUT NOT LIMITED TO ITS CONDITION, QUALITY, PERFORMANCE, MERCHANTABILITY OR FITNESS FOR PURPOSE. Microchip disclaims all liability arising from this information and its use. Use of Microchip devices in life support and/or safety applications is entirely at the buyer's risk, and the buyer agrees to defend, indemnify and hold harmless Microchip from any and all damages, claims, suits, or expenses resulting from such use. No licenses are conveyed, implicitly or otherwise, under any Microchip intellectual property rights.