Hawaslsh
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Hello All,
I am working to create a phase comparator using the AD630. The datasheet provides a circuit diagram on how to setup the AD630 as such. However, as I was working my way though my first experiment, I ran into some issues I couldn't quite solve on my own.
Above is the circuit diagram I am using. It's straight from the datasheet (page 16), expect I am using Amp A instead of amp B. The two inputs are the same frequency, however, the phase of channel 2 can be varied 180 degrees. The photo of the oscilloscope above displays the output from the phase comparator using this setup. Unless my understanding of phase detectors is wrong, the output is failing to switch on any of the reference's edges. If I vary the phase of the reference; the output simply tracks the input and maintains that 50% duty cycle with only negative pulses. Hope that makes sense.
After trying a lot of different things, somehow I managed to get what I think is a correct phase comparator output. The only change to the circuit was removing the ground reference from the SELB comparator, and adding the shunt 10K resistor between the input and SELB. Now the output trace switches at every refence and input edge. If I vary they phase of the reference, the duty cycles of the positive and negative pulses are determined by the phase offset.
I have no clue why that worked, or if that is even a good solution to the problem. Perhaps its a result of using a breadboard and the fact the datasheet stresses star ground connections? Does anyone have any suggestions as to why this worked and if this solution might cause problems down the line? Bonus question: if this circuit were to be create on a PCB, would a continuous ground plane count as a star ground connection?
Please let me know if you have any questions or need any more context. Thanks in advance for any and all help,
Sami
I am working to create a phase comparator using the AD630. The datasheet provides a circuit diagram on how to setup the AD630 as such. However, as I was working my way though my first experiment, I ran into some issues I couldn't quite solve on my own.
Above is the circuit diagram I am using. It's straight from the datasheet (page 16), expect I am using Amp A instead of amp B. The two inputs are the same frequency, however, the phase of channel 2 can be varied 180 degrees. The photo of the oscilloscope above displays the output from the phase comparator using this setup. Unless my understanding of phase detectors is wrong, the output is failing to switch on any of the reference's edges. If I vary the phase of the reference; the output simply tracks the input and maintains that 50% duty cycle with only negative pulses. Hope that makes sense.
After trying a lot of different things, somehow I managed to get what I think is a correct phase comparator output. The only change to the circuit was removing the ground reference from the SELB comparator, and adding the shunt 10K resistor between the input and SELB. Now the output trace switches at every refence and input edge. If I vary they phase of the reference, the duty cycles of the positive and negative pulses are determined by the phase offset.
I have no clue why that worked, or if that is even a good solution to the problem. Perhaps its a result of using a breadboard and the fact the datasheet stresses star ground connections? Does anyone have any suggestions as to why this worked and if this solution might cause problems down the line? Bonus question: if this circuit were to be create on a PCB, would a continuous ground plane count as a star ground connection?
Please let me know if you have any questions or need any more context. Thanks in advance for any and all help,
Sami
