# Design Active Filter for audio (60hz-20Khz) with configurable gain, single power supply

I am trying to design an Active Band Pass filter, to pass frequencies 60Hz (220 v electricity noise) to 20K, part of ADC system. My source signal is coming from Piezoelectric sensor, which means more than 100K ohm impedance, whith volatage levels between 100/200 mv p-p. i'd like to get output voltage of 1V p-p I would like to build the buffer to 'translate' the impedance into a very low impedance.

limitation : 1 single 5v power supply.

I am using MCP6021/6022/6024 opamp , for the unity gain active filtering, and TI PGA2311 to apply the configurable gain.

I found in the MCP6021 datasheet a typical application in a ADC buffer,

and I tried to integrate this circuit with the PGA, So my current design absence that my negative voltage is getting cut (the source signal has no offset...) So I need your help in the following problems : 1. how to create a DC bias? 2. how to improve the LPF ? i tried to simulate with CircuitLab and i get not the best graph... 2. how to add HPF to filter bellow 60hz?

This is the current design - lack of DC bias, and without the HPF for fc=60hz

Thanks a lot.

• Give the analog filter wizard a spin: analog.com/designtools/en/filterwizard Beware the results - they can sometimes be a bit unstable but this will give you an idea of where to start. Jan 8, 2017 at 16:38
• You need to clarify your priorities in this design. Single supply and split supply I2C controlled PGA2311 can be solved with compromise to dynamic range or creating a -5V charge pump. Undefined are goals, specs for cost, THD, size, complexity, qty. DC bias is trivial if you have AC coupled source and pullup/down R to V/2 on input, but then you need to AC couple output. -5V also improves dynamic range from clipping. so you decide SPECS pls. It can be done with 1 Op Amp only or 3 depends on SPECS. Jan 8, 2017 at 16:47