| selim |
Hi All,
Most of the circuits I have seen here in this forum and elsewhere
utilize a single transistor for the VAS. Mr.Self, describing his
'Blameless Amplifier', maintains that it is best to use a darlington
connected pair for the VAS.I would like to hear your opinions
on swapping this darlington configuration with a Sziklai pair.
One downside I can think of is, in a darlington connection as in
Mr. Self's amps, the input transistor of the darlington pair
operates in an almost constant Vce because the collector is
tied to the ground.In a CFP configuration, both transistors
making up the VAS will see the rail-to-rail excursion, forcing
the first transistor to be a high voltage type as well.
Selim |
|
|
| peufeu |
Sziklai has advantages for voltage followers but the VAS is just a current amplifier, so using a darlington or a CFP is about the same.
View the input stage as a current source (it converts the error voltage into a current) if you have problems understanding this.
If you don't use a current mirror in the input stage, it's a bit less clear, though... |
|
|
| mikeks |
| quote: | Originally posted by peufeu
......the VAS is just a current amplifier....... |
Nyet. Transimpedance amplifier. |
|
|
|
