Which is better to get a symmetric swing of the output signal?

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samy555

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For the following voliage divider config.



Is it better to make VC= 0.5 VCC or VCE= 0.5VCC?

thanks
 

The second alternative with VCE=0.5*VCC is more symmetrical than the first one.
 

but signal is taken from collector to GND!
 

Example:
Vcc=20V
Bias point: VCE=10V; Ic*Rc=8V; Ic*RE=2V
Vcoll=20V=12V+8V (Ic=0)
Vcoll=20*Re/(Rc+Re)=4V=12V-8V (Ic=max, VCE=0V).

Therefore: Vcoll=12V(+-)8V.
Comment: Assumption Vce,sat=0

Result: Symmetrical operation for VCE=0.5*VCC
 
Last edited:

OK
another question: If I have two designs (like the above one) which are the same except that one designed around IC=0.1 mA and the other has IC =10mA
I know that the first maintains the battery and has larger input impedance and larger output impedance than the second.
are there other differences between?
thanks
 

The most important difference is gain.
The transconductance gm=Ic/Vt is direct proportional to the collector current Ic.
 

but the Av gain is roughly = -RC/RE
 

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