skythunder
Junior Member level 3
Hi,all,
Here is a bandpass filter with a higH Q biquad architecture, and this is from Allen's notes.
Obviously, this biquad contains a charge amplifier(the first stage) and a noninverting SC integrator,plus a switched capacitor and a capacitor as feedback into input.
I think this filter has no gain. In the first stage, the gain is the ratio of C0 to C1 (C1 is much larger than C0);
In the second stage, the gain of the integrator is related with the ratio of input signal frequency to the sample clock frequency.
There is a magnitude response vesus frequency ratio of integrator in Allen's book, my signal of interest (120K) is less than one tenth of the clock(1.5M), so there is a little gain which is more than 1 a little bit.
In total, there is no gain since the first stage attenuate the signal too much, while the two feedback capacitors can't help increase the gain.
Therefore, my question is : can this architecture be used as basic block in a cascade architecture to be a high Q bandpass filter ? I think it attenuate signals too much!
I hope I can get some different opinions .
By the way, the possible drawbacks of my opamps : about 0.6 mV DC offset, 9 MHz UBW with 10pF capacitive load. I am not sure how much bad effects can these drawbacks bring ?
Here is a bandpass filter with a higH Q biquad architecture, and this is from Allen's notes.
Obviously, this biquad contains a charge amplifier(the first stage) and a noninverting SC integrator,plus a switched capacitor and a capacitor as feedback into input.
I think this filter has no gain. In the first stage, the gain is the ratio of C0 to C1 (C1 is much larger than C0);
In the second stage, the gain of the integrator is related with the ratio of input signal frequency to the sample clock frequency.
There is a magnitude response vesus frequency ratio of integrator in Allen's book, my signal of interest (120K) is less than one tenth of the clock(1.5M), so there is a little gain which is more than 1 a little bit.
In total, there is no gain since the first stage attenuate the signal too much, while the two feedback capacitors can't help increase the gain.
Therefore, my question is : can this architecture be used as basic block in a cascade architecture to be a high Q bandpass filter ? I think it attenuate signals too much!
I hope I can get some different opinions .
By the way, the possible drawbacks of my opamps : about 0.6 mV DC offset, 9 MHz UBW with 10pF capacitive load. I am not sure how much bad effects can these drawbacks bring ?