i want to design a active bandpass filter, Q>10, center frequency f0=20KHz, stop band attenuation as large as possible, and use as small as possible external components, and only one off-chip component is allowed (a R or a C), the other components to be on-chip, what type of BPF can i use?
in my opinion, i want to design a two-order BPF, but as i know, f0 is usually decided by at least two R and two C, such as f0=1/(sqrt(C1*C2*R1*R2)*2*pi), so if i use only a R or a C to tune the f0, the linearity is not better.
besides, the opamp non-ideal characteristics can have much influence on the BPF performance. so, how to consider this or how to design the opamp parameters (such as DC gain, GBW, PM, etc).
thanks all.

Define your requirements better

"Out of band rejection as high as possible"

Needs to be quantized.

After that? Define you S-plane function as needed.

Also, consider an ADC and a FIR filter at that low a frequency.

gmC that low? Nowadays I don't do gmC till I get above 20MHz.

The power of GmC can be high for lower frequencies.

The minimum power is really set by the technology.  So below a min frequency the area and power is not used efficiently.

lhlbluesky_lhl wrote on Oct 22^nd, 2012, 5:10am:


You can do a gmC filter at any frequency but the transconductor
design often requires a lot of bias current to maintain linearity

Generally I will use a gmC filter for higher frequency applications
(20-500 MHz) and below that look into something based upon op-amps,
switched capacitor design or ADC and FIR filter.

If you are going to hit an ADC anyhow, I would use a minimal
filter for aliasing and then ADC and FIR filter.