# Cascode Output Capacitance Calculation (BJT/HBT)

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#### striderZA

##### Newbie
I am designing a bipolar cascode amplifier and I need to calculate/estimate the output capacitance.
Here is the reference circuit (from https://ocw.snu.ac.kr/sites/default/files/NOTE/5788.pdf): Because the voltage gain of Q1 is Av=1, we can use Miller's theorem to determine the effective input and output capacitances of the CB stage. These are Cπ1+2Cμ1Cπ1+2Cμ1 and CCS1+2Cμ1CCS1+2Cμ1.
What I don't quite understand is that the notes referenced above state that CCS12CCS1 and Cπ1Cπ1 are in parallel, and CCS22CCS2 and Cμ2Cμ2 are also in parallel. Why is that?
--- Updated ---

I am designing a bipolar cascode amplifier and I need to calculate/estimate the output capacitance.
Here is the reference circuit (from https://ocw.snu.ac.kr/sites/default/files/NOTE/5788.pdf): Because the voltage gain of Q1 is Av=1, we can use Miller's theorem to determine the effective input and output capacitances of the CB stage. These are Cπ1+2Cμ1Cπ1+2Cμ1 and CCS1+2Cμ1CCS1+2Cμ1.
What I don't quite understand is that the notes referenced above state that CCS12CCS1 and Cπ1Cπ1 are in parallel, and CCS22CCS2 and Cμ2Cμ2 are also in parallel. Why is that?
Parallel combinations should be CCS1 + Cpi2 and CCS2 + Cmu2, seems that latex commands broke.

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