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Using PLL’s Phase Detector as a Linear Phase Meter

Question asked by SouthPacific on Oct 21, 2012
Latest reply on Nov 5, 2012 by SouthPacific


I’m exploring circuits that could make a Linear Phase Meter. While I’d like to operate from 10Hz to 10MHz with 0.1 degree resolution - I’m willing to see what I can get – with standard parts. I’m expecting lower resolution and accuracy at the frequency extremes though.


I’ve prototyped a number of solutions including Balanced Modulators and Analogue Multipliers. The AD8302 is very non-linear around 0 degrees.


I’ve also been looking at Phase Frequency Detectors and Charge Pumps – predominantly what’s inside NXP’s 74HCT9046 PLL. I am getting very strange results that don’t make any sense. While I may have got something wrong, I’m also wondering whether parts like this are just not designed for such an application.  I have never seen circuits showing these parts used in such a way. Mainly I see theoretical documents.


I’ve discovered the AD9901 Phase Frequency Discriminator (still need the Charge Balance circuit) which looks promising and realize that Analog Devices may have something more suitable that might work. Might there be a part I should consider?


Is using the Phase Detector and Charge Balance sections from a PLL going to work as a Linear Phase Meter – or are these sections designed to keep the PLL functioning? i.e. don’t use them open loop?