I am in need of a generic band pass filter for one of my project. I am making a signal generator which generates square, sine signal from frequency 50 Hz to 10 MHz. I am going to generate a square wave using an inverter. But i want to design a band pass filter to make square wave.I can't figure out how to design a band pass filter that adjust itself when we continously change the frequency of square wave.

 

Bandpass filters are not generally used with square waves unless you want to introduce large amounts of distortion by rounding of the corners.

 

Do you mean you want to filter the square-wave to make a sine-wave?
Band-pass filters with variable center frequency and band-pass are difficult to make.

 

How about these two:
http://www.ebay.co.uk/itm/0-30MHz-D...884180?hash=item28249bd4d4:g:pI4AAOSw0vBUdGoj
http://www.ebay.co.uk/itm/AD9850-DD...287407?hash=item21165061af:g:sAgAAOSwgmJXzTHI

 

Do you mean you want to filter the square-wave to make a sine-wave?
Band-pass filters with variable center frequency and band-pass are difficult to make.

Yes I want to filter the square wave to make sine wave. What about using a programmable band pass filter.

 

Yes I want to filter the square wave to make sine wave. What about using a programmable band pass filter.

50 Hz to 10 MHz is an enormous frequency range, and I seriously doubt you will find any sort of programmable bandpass filter that will cover that spectrum. Whether voltage tunable or digitally tunable, programmable filters are a major design challenge.

In any case, filtering a square wave to obtain a sine wave is doing it the hard way; it is much, MUCH easier to generate a sine wave over that frequency range by direct digital synthesis (DDS), using chips such as the AD9833 or the AD9850. The AD9850 is a very popular chip and there are numerous inexpensive frequency synthesizer modules available based on it that can be easily interfaced to an Arduino or other microcontroller.

 

Linear Technology and Maxim make switched-capacitor filter chips that are tuned by changing a clock frequency. But the filter clock must be many times the freq of the signal. For example, if you generate a 50 kHz square wave and divide it by 50 to produce a 1 kHz square wave, the 50 kHz is the clock for the filter and the 1 kHz is the signal being filtered. As you change the 50 kHz clock, both the filter passband and the input signal change together, always tracking. This is great for lower signal frequencies, but I don't know of any parts that wil operate up into the MHz region.

ak