I have a software filter that multiplies the input signal with a sine and cosine wave (I,Q). After multiply the complex output is square rooted to get the amplitude.
What would be the name of this kind of filter?
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Hi Vinzz,
What you are describing is not a filter. The multiplication by sine and cosine of frequency f0 is called quadrature conversion. It converts a signal centered at frequency f0 to a complex baseband ("I/Q" or "I + jQ") signal.
To get the amplitude, you take the square root of I^2 + Q^2.
regards,
Neil
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If that is the case then the frequency of the sine and cosine would be irrelevant?
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The frequency of the sine wave (aka, local oscillator, in a tuning application) determines which frequency gets mixed (translated) to baseband (DC, zero frequency). That's how a radio tuner functions.
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Vinzz,
Try looking up "quadrature down-converter" in a textbook or online.
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+1 that that's a mixer followed by an amplitude detector. What you're describing is a tuner and a demodulator for AM radio.
Usually that does include a filter, but the process you described didn't include one.
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If I understand your description correctly, you are finding the envelop of the signal. kind of Hilbert Transform usecase...