Hi, everyone! I know the HMC984 is a charge pump PFD and i'm wondering the way to use it to measure the phase error between two input signal REF and VCO.
- First, can i make the assumption that +phase error corresponding to sourse current and -phase error corresponding to sink current? And the pulse width is decided by the phase error.
- Second, if i use a passive loop filter , is it possible to get a negative voltage that represents the -phase error at the output of the filter . If not , is it possible to implement this with a passive loop filter and how to realize it?
Thanks for help!
For first question, see here, In short - yes this should work
For second question…
For second question, see here on how to design loop filter with this device.
You can't get a negative voltage at the HMC984's output, but it can handle negative gain Vtune curves by flipping PFD polarity, See "Phase swap" section of the datasheet
Hi! Sorry to bother you again. I have one simple question, does HMC984 support single ended input(VCO input)? Can i connect VCON to the ground through an ac couple capacitor, and connect the single ended input to the VCOP through an ac couple capacitor? Thanks.
The HMC984 requires an open collector input at the VCON/VCOP pins. So if you are not planning on using the HMC983 you will need some other external buffer IC. I do not have an appropriate one to recommend you other than the HMC983. It is important to ensure the voltage swing does not exceed 875mVpkpk or go below 625mVpkpk at the VCOP/VCON pins.