Why is the current gain of the CE amplifier negative? (BJT)

[purnapragna]

hi i have a doubt that why is the current gain of the CE amplifier is negative? Can anybody explain it with the help of basewidth modulation?

thnx

purna

 

[demodb]

Re: question about BJTs

i don't think it has anything to do with basewidth modulation. The fact it is negative just gives information about its direction and nothing else.

 

[yjkwon57]

Re: question about BJTs

Hi~~

The current gain in the CE configuration is increased as Vce is increased due to the base width modulation. As Vce is increased, the effective base width is decreased, then, the slope of the minority carriers becomes steeper, then, the velocity of the minority carrier is increased, thus, the collector current is increased.

Bye~~

 

[sp]

question about BJTs

it is "base width" and not basewidth(bandwidth?)

CE configuration is an active low type of configuration...

asserting the base will pull low the node at collector(wth a resistor on top of collector)...

so the gain is negative... u can try it in PSPICE to see the amplifying effect is opposite direction...

sp

 

[e_eja]

Re: question about BJTs

CE configuration increase voltage and current gain so theres no reason to have negative gain on CE configuation, you have to reanalize more detail about your simulation
regards

 

[Eric Best]

Re: question about BJTs

hi i have a doubt that why is the current gain of the CE amplifier is negative?

Your doubt is right - the current gain of the CE amplifier IS POSITIVE as an increasing/decreasing input current (consequently Ib) causes an increasing/decreasing output current (consequently Ic).

I think you have mixed it up with the voltage gain (CE), which is negative as an increasing/decreasing input voltage (consequently Vbe) causes a decreasing/increasing output voltage (consequently Vce), i.e. phase shift 180 degrees (or PI) between output and input voltages.

Best Regards
Eric