In Reply to: Re: LM565 test circuit posted by Kapil Gore on 08/14/02 at 6:23 PM:
The LM565 has finite loop gain, so drift in the VCO free-running frequency will cause a phase stress (a few degrees from 90). A frequency offset of 25 Hz will also cause a small phase stress.
If your input is continuous, low-noise, and is digital or can be converted to digital, I would consider the 74HC4046, using phase comparator PC2 (the part has 3 different intermal phase comparators to choose from). This will give you (nearly) zero degrees phase shift between input and output, and it will not change due to temperature, voltage, frequency shift, or phase of the moon.