PLL as modulator og demodulator
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From: Winfield Hill on 28 Mar 2006 09:01 rasmusms wrote... > > Do you know who makes the MC145170? I can't find it on > fairchild/motorola homepage anymore. The modern pin-compatible version is the mc145170-2, which had a new 32-page rev-5 Freescale datasheet issued last year http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=MC145170_2 The official p/n was the mc145170P2, D2, DT2, etc. Freescale (the Motorola RF semi spinoff) has dropped the part (along with many other "legacy" ICs), perhaps to avoid making RoHS versions, but some are available from surplus distributors. Lansdale Semiconductor is offering a version, the ML145170. Get a 13MB (!) datasheet on their webpage, www.lansdale.com > Do you have a example on an appnote? Two classic appnotes were the an1207 and the an1671. -- Thanks, - Win
From: rasmusms on 6 Apr 2006 07:22 Is it possible to avoid varying the loop gain by detecting on the output from the phase comparator and not after the loop. So the loop stays constant looked on carrier frequency ( rescieve signal has both carrier and one of the FSK frequencies)
From: Andrew Holme on 6 Apr 2006 08:01
"rasmusms" <rasmusms(a)gmail.com> wrote in message news:1144322554.793411.94160(a)j33g2000cwa.googlegroups.com... > Is it possible to avoid varying the loop gain by detecting on the > output from the phase comparator and not after the loop. So the loop > stays constant looked on carrier frequency ( rescieve signal has both > carrier and one of the FSK frequencies) > I don't understand what you mean about the receive signal having both carrier and one FSK frequency. That is not how FSK normally works. We're trying to modulate and demodulate FSK using the same PLL without varying the loop gain (or bandwidth) on switching between send and receive. I'll assume the loop bandwidth is narrower than the data rate, to prevent the loop fighting against the modulation on send. So, the loop will filter-out the modulation on receive; and the phase detector output will be a complex waveform with a repetition frequency equal to half the FSK mark / space frequency shift. Depending on the type of PFD used, it might be possible to determine if the received tone was higher or lower than the VCO; but it would probably be easier to change the loop bandwidth. Since you also need to switch the reference input when changing between send and receive, might it not be simpler to use two PLLs? |