Q enhancment using source follower with active load

[komatozo]

Dear all,
Am trying to test different Q enhancement techniques that is used to handle the non-idealities in the on-chip inductors,
currently am working on using an active Q enhancement using a source follower with an active load. can any body advice me about about the advantages and disadvatages in this way and how I can get a high q enhancement out of this method.

 

[Milad-D]

There are some ways to increase the Q of the inductor:

1. cross-coupled gm which produces a negative resistance with a value of -2/gm.
2. The real part of the input impedance of source-follower ( which has a Cl as a load) is -gm/(Cgs*CL*w^2).
3. Some other ways has been proposed in the literature, that use the combination of mutual inductance and transistors to produce negative resistance.

If you want to design a filter, the way you compensate the inductor, is very important. In other words, the frequency behavior of the negative impedance must be as near as possible to the real part of on-chip inductor. As already stated in (2), the negative impedance, produced by source follower has significant frequency dependence which is not desirable. If the targeted bandwidth of the circuit is small, this behavior does not corrupt the filter characteristics that much.

 

[Milad-D]

View attachment Q_enhancement.ppt

Here is a simple literature review about Q-enhancement techniques.