Delta36
Newbie level 2
Could someone please explain how a PLL charge pump operates? And if I need to interface to a high voltage VCO with an opamp, can I simulate that?
I get that it's a switching current source, biased by a voltage source at say 3.3V or 5V source and at it's simplest form it could be a BJT current mirror to provide the constant current, but if I have an active filter (w/ caps in the feedback) how can it source any current other than the tiny dV/dt across the caps?
Also, I'm trying to interface to a 0:13V VCO, but I'd really like to verify the opamp in SPICE. I've got a reference design from Hittite (HMC704 PLL) and I checked the HMC-PLL Designer.exe using that reference design, and the eval schematic and PLLDesigner match (thanks HMC for keeping the two the same).
If I build up that opamp in OrCad (using a pulsed current at the input, 0:3mA), it doesn't make much sense to me. If I use a pulsed voltage (0:4V) it at least kind of makes sense.
Please, could someone try to learn me somethin good?
I get that it's a switching current source, biased by a voltage source at say 3.3V or 5V source and at it's simplest form it could be a BJT current mirror to provide the constant current, but if I have an active filter (w/ caps in the feedback) how can it source any current other than the tiny dV/dt across the caps?
Also, I'm trying to interface to a 0:13V VCO, but I'd really like to verify the opamp in SPICE. I've got a reference design from Hittite (HMC704 PLL) and I checked the HMC-PLL Designer.exe using that reference design, and the eval schematic and PLLDesigner match (thanks HMC for keeping the two the same).
If I build up that opamp in OrCad (using a pulsed current at the input, 0:3mA), it doesn't make much sense to me. If I use a pulsed voltage (0:4V) it at least kind of makes sense.
Please, could someone try to learn me somethin good?