voltage controlled nitch filter
flatulent said:
The superheterodyne method is as follows. You multiply the input signal by a sine wave. Then low pass the output with the bandwidth you want (low pass BW is half of band pass BW) You then multiply the low pass filter output by the same local sine wave and get the output at the same frequency as the input.
Hi flatulent,
Thanks for taking the time out to explain the concept, I have tried to read a book on this topic I think it was called Construction of Spetrum Analyzer(forgot the name of the book..) but as an EE newbie I am stilling trying to grasp the concept eventhough I been a student of EE of 2 years.......
In the explanation above, it sounds like amplitude modulation the input signal but I don't understand the purpose of LP filtering the output and AM it again will achieve?
Sorry about the newbieness...... :?
That is the simplified description. Add to that the fact that the multiplies are quadrature. That is, there are two multipliers, they are fed from the local sine wave and itself shifted by 90 degrees. There are two IF strips and then two quadrature multipliers at the output.
So I guess I would need 2 phase splitter chip or a TI dvr143 chip for the sine wave and the input signal to drive the + and the - terminal of the multiplier?
This is much more expensive than the switched capacitor filter but the SC filter produces clock noise in the output.
If your system already has an ADC and DAC you can do the superheterodyne method in math.
I am aiming to build a digital controlled analog circuit because I am not quite competent yet at programming a DSP chip to do the processing not to mention understanding the math involed in FFT....
My analysis and design project is to build a spectrum analyzer to display the frequencies of music notes up to 8 octaves, I am plannig to use a ucontroller to generate 7 clock pulses(7 notes of the highest octave) and then use divided by 2 counters to create the clock rates of the lower 7 octaves to control the Fc of the bandpass filter.
I am thinking of using commutational switches to switch the output and the clock rates controlling Fc of the bandpass filter in a synchronized manner, then use a
**broken link removed** with a buffer at each Q out to control each switch. Will use the highest clock frequency possible controlling the D type shift registers but I am worried about the switch noise might distort the output of the bandpass filter?
Any thoughts?