Please see attached image. I struggling to understand why Rs is negelected in the input impedance; should'nt the total input impedance be the parrallel combination of the capacitor impedance with the Rpi plus in series with Rs?
Electrical – Cascode Input Impedance
cascodeinput-impedance
Related Topic
- Capacitance – Miller’s Theorem and Input Capacitance
- Electrical – Input impedance of instrumentation amplifier circuit
- Electrical – multimeter input impedance calculation discrepancies
- Operational Amplifier – Measuring Input Impedance of Differential Amplifier
- Analog – Understanding Second Order All-Pass Filter Input Impedance
- Electronic – understanding input impedance theory
- Input Impedance – Analyzing Input Impedance of Class AB Amplifier
Best Answer
Yes !
In the referenced equation, Rs is not referenced. The capacitance is. Clearly the signal at the base of Q1 does depend on the value of Rs -- it is in series with the input signal, and there is (at least) a capacitance to GND.
A little inspection will show that the true impedance is Rs+...