I need to design and build a bandpass filter amplifier for my ECG (ElectroCardiography) project. The band pass filter is to remove noise. Heart signals are between 0.5 and 150 Hz, therefore the bandpass filter should remove noise below 0.5 Hz and above 150 Hz.
I have designed a simple bandpass filter but it doesn't work as it should. It doesn't filter out signals of 200 or even 300 Hz, nor even 500, something is clearly wrong. I've designed it in MultiSim (by National Instruments). I've attached a snapshot of the circuit for you to have a look.
The equation I used was frequency = 1 / 2 * PI * Resistance * Capacitance
I've also attached screenshots for the output at 150 Hz and at 200 Hz , at 200 Hz the output should be reduced if not made zero.
I've used the LF351D because it has high-input-noise impedance so please in your advice try to consider the fact that I'm gonna be using that op-amp.
The question is, is what I did correct ? How can I design an advance bandpass filter which is accurate and reliabel and suitable for the ECG application ? Please help and advise