Good catch. 48 dB it is, not 44.

 

Don't know if this went by before - you filter after the gain stage so the filter attenuates the noise introduced by the gain stage - as long as the amplified signal does not saturate the filter circuit..

1 kHz bandwidth at 28 kHz sounds like a resonant circuit like an L-C or twin-T, rather than a traditional bandpass circuit. The two corner frequencies are so close together that there would be almost 6 dB of signal loss at the center frequency.

ak

 

Don't know if this went by before - you filter after the gain stage so the filter attenuates the noise introduced by the gain stage - as long as the amplified signal does not saturate the filter circuit..

1 kHz bandwidth at 28 kHz sounds like a resonant circuit like an L-C or twin-T, rather than a traditional bandpass circuit. The two corner frequencies are so close together that there would be almost 6 dB of signal loss at the center frequency.

ak

To get the appropriate rolloff with such a narrow passband the order of the filter will need to be raised substantially.

 

If I'm not mistaken, a gain of 250 is 44 db, not 24 db. Aside from that quibble, I think your amplify-filter-amplify recommendation is the most practical one. Myself, I'd probably choose an amplifier with a gain of 10, followed by a 30 kHz 2-pole lowpass filter, then another X10 amplifier to feed into the ADC.

Thank you for your reply. Is it adequate to use only low pass filter to clean up the signal before feed it into ADC?

 

How about low frequency signal noise?

 

To get the appropriate rolloff with such a narrow passband the order of the filter will need to be raised substantially.

For now I'm considering a filter as shown in the attachment.4th order Butterworth bandpass filter with
Gain: 1 V/V
Passband: -3dB at 1kHz
Stopband: -40dB at 12kHz

However, I'm not yet test it or simulate the filter. Any suggestion or comment on this filter?

 

Are you doing any digital processing of the signal?
If so can you do any digital filtering? That's more precise than analog filtering and adds no analog noise. But you need an anti-alias analog filter to sharply attenuate anything above the Nyquist frequency (above 1/2 the sample frequency).

 

Are you doing any digital processing of the signal?
If so can you do any digital filtering? That's more precise than analog filtering and adds no analog noise. But you need an anti-alias analog filter to sharply attenuate anything above the Nyquist frequency (above 1/2 the sample frequency).

Yes, this signal will undergo digital processing and digital filter is under my consideration too. But since it needs sharp attenuation above Nyquist frequency, it means I will need high order filter right?

 

Yes, this signal will undergo digital processing and digital filter is under my consideration too. But since it needs sharp attenuation above Nyquist frequency, it means I will need high order filter right?

It's the Nyquist frequency of the ADC sampling rate as compared to the signal frequency that is of concern.
The higher the sampling rate, the less analog filtering required to do digital filtering.
What is the sampling rate and what is the highest analog frequency of interest?