We are trying to design a high pass filter, which mainly goals are:
- very low noise. Low noise is the first concern.
- suppresses 1kHz by around 50dB and passes 2kHz.
- Gets rid of DC
- Dont care on other frequencies.
Description of our project:
We are to measure a very weak 2kHz signal in accompany with very large 1kHz signal(70dB larger than 2kHz signal) with a 16-bit ADC based Lock-in Amplifier.
Since the 2kHz signal is too weak and we need to achieve a resolution coming from a 16-bit ADC, 2kHz signal has to be amplified first. However, since 1kHz is too large, we have to filter it out first, in order to prevent saturation, before amplification.
About specifications of "how low the noises should be". The requirement is as low as possible. We are willing to try ANY method/combination/components to reduce the noises.
Here are points that I know:
- Need inductors, and at low frequency it may be very hard to find a large and accurate one? (I do not want to make inductor by hand)
- low noises comparing with active filters.
- easy to implement
- relative larger noises...
Need your help!
Since the noises are our most important concern, could I ask for some suggestions on tradeoffs of choosing:
- active filter based on OpAmp,
- active filter based on BJT/MOSFET or
- passive filter?
- implement active filters based on IC
- implement active filters based on switched capacitors
Could I have some general comments?
Any suggestions are appreciated.