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

[samy555]

For the following voliage divider config.



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

thanks

 

[barry]

can't see anything. Repost

 

[LvW]

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

 

[samy555]

but signal is taken from collector to GND!

 

[LvW]

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

 

[samy555]

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

 

[LvW]

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

 

[samy555]

but the Av gain is roughly = -RC/RE

 

[LvW]

but the Av gain is roughly = -RC/RE

Yes, but only for large g values (RE>>1/g). Very often, this does not apply for Ic=0.1mA.