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how to decide LDO's bandwidth used for VCO

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flesher

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Hello, a LDO is used for VCO, for example if VCO's frequency range is 120MHz~330 MHz, how to pick up the bandewidth for LDO?

Thank you in advance.
 

dick_freebird

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I think it's more about the ambient noise sources, like
power supply ripple, local clocks, etc. You would like
the LDO to have a decent high frequency PSRR to tamp
these down at the VCO, where they become phase noise /
jitter contributors. At 100MHz+, you really have to count
on decoupling caps rather than active circuitry to roll
off self-generated "noise".
 

flesher

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hi, freebird, thank you very much
 

saulbit

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I don't uderstand you very well. Do you mean to use
the LDO to limit the radiation part of your VCO output? Ah, since your frequency is not very high, so any LDO will do
 

jt_rf

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agree with dick_freebird. Maintaining high psrr at VCO frequency is simply not practical with limited Iq of LDO. Such things need to be taken care at system design level.
 

FvM

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The topic is IC design. So you can most likely not rely on bypass caps.

Utilizing a voltage regulator for VCO PS interference suppression is a realistic scenario. It has considerably improved
the PLL performance of recent FPGA designs, e.g. Altera Cyclone III. Of course, there can't be external bypass caps at
the regulator output.
 

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