while designing the filter(low pass filter) , which one is better means active filter(using opamps) or passive filter (only r and c ). which filter is better and accurate for filtering with out noise...
while designing the filter(low pass filter) , which one is better means active filter(using opamps) or passive filter (only r and c ). which filter is better and accurate for filtering with out noise...
The answer depends on the requirements to the filter:
filter order (damping requirements), bandwidth (corner frequency), gain yes/no, tuning capabilities yes/no, .....
The answer depends on the requirements to the filter:
filter order (damping requirements), bandwidth (corner frequency), gain yes/no, tuning capabilities yes/no, .....
Please, be more specific.[/quote]
i want the envelope of the 40khz signal which is transmitted from tx. before transmitting, i have given that to low pass filter so that can have its envelope.see the attachment..
I like passive filters but use more active filters. The reason is that passive filters can prove expensive or require "impossible" components. For your application I would use an active filter.
However, a low pass filter will not give you the signal you show - what you need is a peak detect circuit or AM demodulator, if I understand your requirements correctly. In its simplest form, that can just be a diode, capacitor and resistor. You will still want some filtering before that (40kHz bandpass I would have thought) but then you will still have a 40kHz signal, not the square wave you draw. The AM demodulator will produce the square wave, although with some well rounded corners.
Mr. Keith,
I am agree with your solution but got a curiosity. Is there some other way to do Amplitude modulation than using filters?
As for this problem, I think active filter would be an better option as passive filter may reduce the signal level and information could be lost.
Search the internet for amplitude modulation/demodulation. The is a synchronous technique where the incoming signal is multiplied by the received signal but I have never used it.
It would still involve filtering though.