# Cascading Common-Emitter Common-Collector for maximum power transfer

Hi Am trying to understand what am doing wrong, I connected CE to CC with a small Rload am designing it so Zout of the second stage equal Rload to get Maximum output.

From what i read in CC-amp Zout = RE||(r'e+ ((R1||R2||RS)/Bac)) were RS is the source resistance, i figured since CC-amp is connected to CE-amp then RC takes place of RS.

I reedited the calculation and obviously it came out wrong.

Bac = 100
RS= RC = 1800
(R3 || R4 || RS) / Bac = 18 since RS << R3||R4
r'e + 18 = 30 => r'e = 12
IE = 25mV /r'e = 2.08mA
VE = 6.24V

Zout = RE||(r'e+ ((R3||R4||RS)/Bac)) = 29.7


Recalculate DC for final result

Vth = VE +VBE + Delta= 7.2V
Rth = Bdc(Vth - VBE / IE - RE) = 12500
R3 = Rth * (VCC / Vth ) = 15625
R4 =1/ (1/Rth - 1/R3) = 62500


Tried different ways but nothing, is the cutoff caused by first stage i tried to keep Q1 in midpoint and without CC it Amplifies signal without distortion, is it a cap problem or is it cause the current is to high

thank you for the help • What are you actually trying to do? I don't see a question here. If you make a CC output amplifier, it should be very low output impedance, not to match the load. If you want an output load matching amp, it should be from a series/parallel feedback stage where the output impedance can be designed – Neil_UK Dec 4 '15 at 7:39
• A CC has a a voltage gain of one and low output impedance and high input impedance so connected it to a CE so it should not overload CE but it did by lowering AV of first stage and the signal is distorted when connected to a small load. Am trying to Amplify in CE and use CC to match its Zout with Rload. Also my calculation was it correct to assume RC of the CE replaces RS and why is the signal distorted. Am trying to understand Transistors – ramon22 Dec 4 '15 at 10:37
• Reduce RE2 .... – user_1818839 Dec 4 '15 at 11:17
• When the transistor is conducting, your output impedance is as you calcuated, for the -ve half cycle, the TR turns off, and you're left with RE2 as the output impedance – Neil_UK Dec 4 '15 at 20:43