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TA0038

RF
Part Number TA0038
Manufacturer RF
Description DC ACCURATE FSK MODULATOR
Published Jul 29, 2005
Detailed Description TA0038      A typical, low cost, FSK modulator is implemented by injecting the modulation voltag...
Datasheet PDF File TA0038 PDF File

TA0038
TA0038


Overview
TA0038      A typical, low cost, FSK modulator is implemented by injecting the modulation voltage into the phase lock loop of the carrier synthesizer.
This is done in two ways, by summing the modulation voltage and the loop error voltage together and applying that to a VCO tuning port.
Or, by using a separate tuning port usually having lower sensitivity to voltage changes.
The modulating data would change the carrier frequency by a predetermined amount (deviation).
This, however, causes a frequency error within the PLL that the loop begins to correct for.
The effect of the loop correcting for the frequency errors caused by the modulation is analogous to passing the modulating signal through a high pass filter.
Lower frequency components of the modulation signal get filtered off (or even eliminated).
This results in unreliable communications for random data streams, especially for long strings of non-changing bits.
There have been several solutions developed and ...



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