Q-point Transistor help

[lefty4000]

Hello,

At my university, we are curretly studying transistor amplifiers and such. We have already covered how to find the Q-point with BJT and are moving on to analysis of FET and I still don't quite get it.

Does anybody have any good resources for understanding the q-point?

 

[BradtheRad]

Maybe you've heard about the 'good operating point' for a transistor. I think that's the Q-point (although a few mention it as 'quiescent point' where it produces no noise).

To get an idea what is a good operating point, it will help if you see a few bad operating points. Watching an oscilloscope trace of the output, while playing with the bias and the collector resistor. (Class A operation).

The waveform moves up or down onscreen, according to how much bias current you apply, and the value of the collector resistor.

A bad operating point is generally visible as clipping of peaks or troughs.

You'll notice a good operating point is about midway between those clipping boundaries. This is tricky to get right, especially when you input a strong signal, or try to get a lot of gain, or apply a heavy load.