hi,
I am trying to analyse the effect of the emitter resistor bypass capacitor in a common emitter amplifier configuration (using a voltage divider bias config), in particular the effect on Ib.
I understand that the RE is key for DC bias stability since; an increase in temp causes beta to increase, causing an increase in IC. An increase in IC causes more voltage to drop across RE (increased VRE). And since VB is 'fixed' due to the voltage divider network, then VBE must decrease (KVL; VR2 = VBE + VRE). This decrease in VBE causes IB to decrease which in turn decreases IC. Giving the circuit independence from beta, and hence stability.
That all makes sense to me but when I try and analyse trhe following individual parameters I'm confusing myself.
All parameters of interest:
Ib:
Vo:
Av:
IB:
If RE is bypassed.
Here's what I have come up with:
Vout: will increase (as Ie will increase because Ic would have increased because it has a more direct path to ground. Correct? Or does Vout increase because the bulk of the voltage gets dropped RC.... This now seems wrong due to the way voltage dividers work - wouldn't you want the bulk of the voltage to be dropped across RE in order for Vout to increase ?? )
Av: will increase (voltage gain, Av=Vout/Vin, and Vout would have increased.)
IB: will remain unaffected (DC signal is blocked and will flow through RE, business as usual for DC.)
My best guess regarding the effect on the ac signal into the base, Ib, is that with the bypass cap in circuit, Ib will increase. I am basing this on thinking that Ic would increase (due to less resistance.. i think but now I'm confused). And therefore Ib must also increase due to beta = delta ic/ delta ib relationship.
Thanks in advance
I am trying to analyse the effect of the emitter resistor bypass capacitor in a common emitter amplifier configuration (using a voltage divider bias config), in particular the effect on Ib.
I understand that the RE is key for DC bias stability since; an increase in temp causes beta to increase, causing an increase in IC. An increase in IC causes more voltage to drop across RE (increased VRE). And since VB is 'fixed' due to the voltage divider network, then VBE must decrease (KVL; VR2 = VBE + VRE). This decrease in VBE causes IB to decrease which in turn decreases IC. Giving the circuit independence from beta, and hence stability.
That all makes sense to me but when I try and analyse trhe following individual parameters I'm confusing myself.
All parameters of interest:
Ib:
Vo:
Av:
IB:
If RE is bypassed.
Here's what I have come up with:
Vout: will increase (as Ie will increase because Ic would have increased because it has a more direct path to ground. Correct? Or does Vout increase because the bulk of the voltage gets dropped RC.... This now seems wrong due to the way voltage dividers work - wouldn't you want the bulk of the voltage to be dropped across RE in order for Vout to increase ?? )
Av: will increase (voltage gain, Av=Vout/Vin, and Vout would have increased.)
IB: will remain unaffected (DC signal is blocked and will flow through RE, business as usual for DC.)
My best guess regarding the effect on the ac signal into the base, Ib, is that with the bypass cap in circuit, Ib will increase. I am basing this on thinking that Ic would increase (due to less resistance.. i think but now I'm confused). And therefore Ib must also increase due to beta = delta ic/ delta ib relationship.
Thanks in advance