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Which bias circuit can bring less phase noise to vco?

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pigkiller

pigkiller

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vco bias circuit noise

My bias circuit in my LC-vco design can be as high as to 30% in the noise summary of PSS sim. is it the real
thing?
so who can tell me in practice which bias circuit can bring less phase noise to vco? and it should be in an engineer point of view.
 

vco bias circuit noise

the bais circuit is the cricital part in the noise contribution?
 

Re: vco bias circuit noise

The bias circuit can be a major contributor of noise in an VCO (especially in an LC VCO).

One way to reduce the noise is to increase the length of the bias transistors. This reduces flicker noise from these transistors

Reducing the mirror ratios by pumping more current into the mirror branch is another way. When I say, mirror ratio, I mean the ratio between, external current used (or internal current generated) and the current actually flowing through the differential circuit.

If both are not possible then try to use a simple RC filter at the mirroring nodes (gates) of the major contributors.

You can also try to add some cap at the tail node. (This will definitely affect your frequency of oscillation)

Let me know if any of these were helpful.
 

vco bias circuit noise

My case is in bipolar tech, so flicker noise due to mos is not concerned. as i know, bipolar as tail has more merit than mos, right?
as i use wildlar PTAT to generate current, the largest noise contricution due to RES, which between the common mode point and bipolar, as high as 20%, i have reduce it's value to 500 ohm and it's still the main contributor of noise. why?
i think wildlar strucutre is not suitable to be used as a bandgap of LC-VCO in my case, who can give me a practical bias type to be used as low noise bias of LC-VCO?
 

Re: vco bias circuit noise

Sorry, I've not worked much with bipolar. Why do you say, bipolar as tail is better? Is it only because, it has no flicker noise?

The only thing I can think of right now is to look at absolute values of other major contributors before and after changing the tail resistor " RES". We may then get an idea about how to proceed.
 

Re: vco bias circuit noise

Uasually, bipolar as tail current source generates more noise than cmos in the same
current and headroom consumption.
 

vco bias circuit noise

I wonder if VCO deisgn need any temprature compensation in the bias circuit? If so, to compensation what? voltage swing, phase noise?
or just a power supply independent bias circuit is engough?
or just a simple "res and a mos" current mirror is engough?
 

Re: vco bias circuit noise

pigkiller said:
I wonder if VCO deisgn need any temprature compensation in the bias circuit? If so, to compensation what? voltage swing, phase noise?
or just a power supply independent bias circuit is engough?
or just a simple "res and a mos" current mirror is engough?
Click to expand...




If the VCO is an LC architecture, you should put a regulator to provide the supply voltage of the VCO!

Added after 4 minutes:

You may consider to use a LC-VCO without tail current
 

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