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How we use the MOS capacitance as varactor?

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yellff

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When we design VCO,how can we use the MOS capacitance as varactor?can anyone give me some advice.
 

check this
**broken link removed**

u will find what u ask

khouly
 

Hi

For an LC Tank VCO, you can replace the capacitances with two simple MOS; Drain Source and Bulk are connected to each other as a one port and the gate is another port.
There are some discussions about the Direction of this element, and I have seen both directions in LC tank VCOs.
 

Hi
you can refer to Tsividis's works such as:
"Operation and Modeling of the MOS Transistor," Yannis Tsividis
as well to the best paper entitled: "0.5-V Analog Circuit Techniques and Their Application in OTA and Filter Design," by Chatterjee, Tsividis and Kinget
to find out making varactors in most famous configs. and then VCO but from the paper.

Best Regards,
SAZ
 

thank you very much
 

Just short drain and short , use gate as a control , it will behave as a capacitor.
 

some design kits contains an accumulation mode varactor , instead of putting the n+ regions inside p-well, they put it in an nwell, so that the charaterisitics of the mos capacitance behave in a monotonic manner
 

nassim_el85 said:
Hi

For an LC Tank VCO, you can replace the capacitances with two simple MOS; Drain Source and Bulk are connected to each other as a one port and the gate is another port.
There are some discussions about the Direction of this element, and I have seen both directions in LC tank VCOs.



"There are some discussions about the Direction of this element, "


i am confused about the direction too, can someone give the details about it?
 

I layout a p-varactor and a n-varactor,how much different are they in the
capacitance change rate with the gate voltage?
 

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