Shunt Feedback Voltage Follower

[hrkhari]

Hi Guys:

Attached is a topology of a shunt feedback buffer. M2 provide shunt feedback and that M1 and M2 form a two pole negative feedback loop. This circuitry draw least power consumption compared to the common source follower buffer stage .Due to voltage headroom limitation I'm using a resistive degenerative load, which forces, M1 in a large aspect ratio, further increasing the parasitic capacitance, which limits the tuning range of my cascaded VCO, I would appreciate if suggestion can flood in the biasing load of this source follower. Thanks in advance

Rgds

 

[paulux]

Could you explain more about your question? Do you want a large tuning range using the shunt feedback voltage follower or do you want to modify the shunt feedback voltage follower in your delay cell(I guess) inside of your VCO?

 

[hrkhari]

Hi:

I had tried integrating a source follower for isolation, but the isolation given is only about 20dB, integrating an fT doubler stage or a open drain buffer requires high power consumption and increased number of transistors which degrades the phase noise performance of the VCO, this FVF (Flipped voltage follower architecture) gives a 28dB of isolation but the flat band unity gain extends to only about 1GHz, any suggestion in extending the flat band unity gain frequency range?. Thanks in advance

Rgds

 

[gevy]

Read following article about this circuit

 

[paulux]

Hi hrkhari,

Since I don't know the exact circuit you now have, I guess the following.....

If you want to have better isolation in a simple structure, it seems to me that is the best you can do as you had already applied the feedback structure. Higher isolation is possible only if you can incorporate complicated feedback structure. This further degrade the bandwidth that it's not worth.

 

[montage2000]

this circuit may not work good , because M1

Added after 50 seconds:

this circuit may not work good , because M1 may work in triode region, give it up, use saturation MOS as a loading

 

[pillar_chen]

is it push-pull output?

 

[eecs4ever]

a more detailed explanation of this circuit.

Looks interesting.