Ok, the fact that my R3 was not changing the signals made me double check the circuit and it turned out that this R3 was not attached to ground 
I probably removed it when changing from a dual opamp (both amps working) setup to a single amp operation we have now.
After fixing this ground issue i now have some signal change when turning this pot.
I have returned the circuit to the original one, so with the 4 diodes and 10K input R1 like below.
The phase shift is still there but much less.
Itsu
Itsu,
You have reduced the error by reducing the hysteresis, but with the different Vfwd's on D5 an D6 due to the assymetrical rails, this error will vary as you vary the amount of hysterisis.
My suggestion would be to operate the comparators on just the 6 volt rail, generate a mid-rail reference (buffered voltage divider) to use for signal ground connections, and AC couple the inputs. Your waveforms will be symmetrical and that symmetry will not change as you adjust hysteresis.
Regarding the noise issue, I would add some analog signal conditioning in front of the comparators. Consider adding an AC coupled variable gain stage and a LP filter in front of the comparators. What order of filter you will need is dependent on the amount and type of noise you are dealing with (a 4th to 8th order filter comes to mind). With a sufficiently slow loop filter at the PLL, truly random noise (i.e., white noise) will average out to a zero phase error. Non-random noise (i.e., spurious or synchronous signals) can be a bit more problematic, but with a LP filter of sufficient order, adjustment of comparator hysteresis, and a slow PLL loop filter, their contribution to phase errors will be reduced significantly.
Using identical analog front ends (i.e., the same gain, filter, and comparator circuits) will null out the phase shifts caused by these stages.
Fixed frequency analog filters will need to be modified for operation at each of the various frequencies you mentioned. If you need truly variable frequency capability, there are some switched capacitor options available to use as tracking filters, but at frequencies greater than 100KHz, these options become limited and more complex. However, I would think variable frequency operation over a large bandwidth would be unnecessary unless you plan to somehow vary L1 or C1 by large amounts during operation. Modifying the passband of fixed filters for each of the desired frequencies of operation would be a simpler solution.
Using diff amps at the front-end would allow detection of I and V with a non-ground referenced L1/C1 (i.e., using a sense coil and a matched pair of voltage dividers for I and V detection).
I would also consider adding an adjustable mono stable between one of the comparator outputs and its PLL input to allow for adjustment of I/V phase.
You mention Ruslan type circuits. However, can you provide more details as to why L1 and C1 are being driven by an opamp in the OP schematic?
PW
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Topic: Conventional (non-OU, but related) electronic circuit problem (Read 7993 times)
