Randy Yates writes:
"Phil Allison" writes:
"Trevor Wilson"
"RichD"
Who do MOSFET sound better than bipolar, as an audio amp output
driver?
**Non-sequitur. If you're saying that MOSFET outputs sound better, they
don't.
As a device,
** Same old red-herring ******** from know nothing Wilson.
It is totally irrelevant how DEVICES behave on their own.
Only when they are properly configured and suitably biased in a
complimentary output stage can performances be compared.
operating at typical bias currents (say) 10-50mA, MOSFETs
exhibit VASTLY more THD than BJTs.
** UTTER ******** !!!
No it's not.
When configured in typical amplifier topologies, THD is vanishingly small at
all power levels and with minimal bias current.
That may be true, but only because of the negative feedback that Trevor
referred to. The basic device IS more nonlinear.
It comes down to device physics. MOSFETs, when operating in the
saturation region, have a square law relationship between Vgs and
Ids. It is only through either a) the application of negative feedback,
or b) the reduction of input level (the smaller the operating range, the
more approximating linear the Ids/Vgs relationship becomes) that the
device distortion is mitigated.
PS: See, e.g., [gray] and [razavi].
--Randy
@book{gray,
title = "Analysis and Design of Analog Integrated Circuits",
author = "Paul R. Gray and Paul J. Hurst and Stephen H. Lewis and Robert G. Meyer",
publisher = "Wiley",
edition = "fourth",
year = "2001"}
@book{razavi,
title = "Design of Analog CMOS Integrated Circuits",
author = "Behzad Razavi",
publisher = "McGraw-Hill",
year = "2001"}
--
% Randy Yates % "So now it's getting late,
%% Fuquay-Varina, NC % and those who hesitate
%%% 919-577-9882 % got no one..."
%%%% % 'Waterfall', *Face The Music*, ELO
http://www.digitalsignallabs.com