Propeller Head Plaza

Technical and scientific discussion of amps, cables and other topics.

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Re: I fixed a bias problem in my Mosfet follower (experiment #1 continued)

Posted by 13th Duke of Wymbourne on July 1, 2003 at 14:05:05:
Kurt,
before delving into the esoteric topologies and transistor types please investigate that the basic design is correct. You're not looking for much power so that's a plus but what load resistance are you driving to determine how much voltage, and consequently how much current swing is required. Dynamically the peak current demanded by the load may be higher than a simple V/R calculation (if the impedance changes with signal level). This is important because the source follwer has to be biased at at least that current. A follower is class A, there is no dynamic current headroom from the power supply capacitance of a class B amp (well, only on the positive cycle).
Is the assymetry you see due to amplitude limiting or due to current limiting on the negative cycle, where the pull-down is trying to sink current from the load? Do you have access to a 'scope?
How to you set the output commom-mode point? Is it controlled by an overal feedback loop to be 0V or are you open loop and tweaking something to keep the output at 0V?
Regards
13DoW