Determine by inspection if classA-E amp ?

[StoppTidigare]

Hi, I am interested of the rules of thumb(do they exist ?) commonly used
when designing biasnetworks to class A to E amplifiers.

Is it possible to determine the class of an amplifier soley
by inspection of ratios of the voltagedivider resistors of the base bias networks ?

Regards,
StoppTidigare

 

[flatulent]

clues

A, B, and C have the same circuit topology and you can calculate the bias point to find the class. D and E have their own unique topology.

 

[StoppTidigare]

OK, but what can be said about the rules of thumb ?
Suppose that I have a BJT, with beta=300, an emitter resistor Re,
a collector resistor Rc, and a voltage divider at the base R1 and R2
R2 connected to ground.

What can then be said about class A,B,AB,C ?

Regards,
StoppTidigare

P.S. Does anyone have a link to the differnt kinds of classes ?

 

[flatulent]

two subclasses

Class C will have no bias or reverse bias on the base.

Class A will have enough bias that the drain current will be large.

Class B will have a very small collector current.

Class AB will be between A and B.

A simple way to calculate bias is to determine the base voltage with the absence of the transistor. Subtract 0.6 V from this to get the emitter voltage. The emitter voltage divided by the emitter resistor will give the current.

 

[StoppTidigare]

Will a frequency amplification amplifier always work at
class C ?

Regards,
StoppTidigare

 

[flatulent]

minimum drive

The class C will not have any output unless the drive level is high enough. It also will have the lowest gain of the a, b, c tyes. You pay a penalty for efficiency.