I have designed a lowpass filter of corner frequency = 50 kHz. According to TI's "Filter Design in Thirty Seconds", I build the schematic in LTspice as follows:
The Op Amp LT1126 has following parameters:
Gain-Bandwidth-Product: 65 MHz
Slew Rate: 11V/µs
I choose LT1126 bacause it is available in my lab and I want to use it in a bandpass filter circuit. I thought the two parameters are far more than enough for this LPF. However, there is a very high frequency component of about 20.9 MHz in the output signal. As shown in the following two pictures:
What is the reason of this phenomenon?
Actually, I have built a bandpass filter (fc = 42 kHz, B = 5 kHz) with LT1126 using the "Narrow Band Pass Filter" design in "Filter Design in Thirty Seconds". But there is also a similar high frequency component in the filter's output. So I tried to simulate the simpler LPF in LTspice and observe the similar result.
As far as I have read, GBP and slew rate are the critical parameters for designing a filter. But with above mentioned results I am pretty sure that there must be something I miss here. Can someone give me a hint?
Or more specific: an Op-Amp of which parameters should I choose to implement a bandpass filter with: fc = 42 kHz, B = 5 kHz and Gain > 1?