I designed a multiple feedback band pass filter
input voltage = 100kHz sine wave, 80mV amplitude gain = 2 AV, center frequency = 100kHz pass-band = 10kHz output voltage => centered around +2.5V supply voltage => +5V
Design restrictions are that I must use a single-supply operational amplifier.
Calculations were taken off Op-Amps For Everyone, and I got the desired result with two opamps: OP27 and OP355NA
Points to Note:
- Tried multiple JFET op-amps as listed below
- Used ideal op-amp to check that calculations are correct
The below circuit was constructed and tested on both Proteus and LTSpice software. Both yielding the same results, which were expected.
Analogue Analysis (Gain of 2, centered around 2.5V)
Frequency Response (Center Fre at 100kHz)
The issue is that these parts are either surface mount (OP355NA) or very expensive (OP27). I can't afford to pay more than 20 dollars for an op-amp.
These are the single-rail op amps I have available at my disposal, and none of them work as expected!
I will be using TL071 and TL074 to simulate from now one.
All op-amps are outputting a very similar result, the following output is from TL071, tested on both Proteus and LTSpice. Here, I present the LTSpice version.
(Center Frequency shifted to the left)
As can be seen, the gain is incorrect and the central frequency is shifted to the left. This was a recurring theme for ALL op-amps I have available.
I know that the op-amps listed above are all different, but they should all be able to provide an output peak to peak voltage of 1V at 100kHz. The following characteristic graphs are for the TL071 and TL074, both of which give the same incorrect response.
The utility-gain bandwidth is 3MHz.
Surely I am missing some important specification, which I'm not taking into consideration, but I find it very strange that none of the above op-amps work properly for my current task.
Thanks to the helpful comments and answers it looks like I underestimated my circuit requirements - Mainly the attenuation from the input resistance ratio (40dB)
Looks like you're trying to get a Q of around 20-40, just eyeballing it, so the GBW is going to have to be that much higher than the center frequency, and preferably 5-10x that, so more like 10-40MHz.
- Why do I have a Q of around 20-40? Isn't Q the (center frequency/BW) or 100k/10k (=10) in my case.
- Also, why should my GBW be around 5-10x the center frequency? Are there any calculations one should refer to or anything of the sort?