Semiconductor Devices: Miller's Theorem

Here, we define Miller's Theorem and then examine it's effect on the input impedance of a single stage BJT amplifier. The theorem states that if an impedance is placed across an inverting amplifier (i.e., from input to output), it will create an equivalent input shunt impedance equal to the feedback impedance divided by the quantity gain magnitude plus one, and an equivalent output shunt impedance equal to the feedback impedance times the gain magnitude and divided by the quantity gain magnitude plus one. Zin-miller = Z/(|A|+1)and Zout-miller = Z|A|/(|A|+1). Collector feedback is the bias of choice here, with the base feedback resistor being in the Miller position, connecting input and output (base and collector).
References: Semiconductor Devices: Theory and Application; Chapter 6, section 4; and chapter 7.
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[@simonyoungglostog]

Great stuff Prof. Simple but effective use of voltage divider to measure the in-circuit Zin.

[@EEE-iw3fk]

Amplifier's input impedance should be infinity to use Miller's theorem?

[@ElectronicswithProfessorFiore]

No, not all. The Millerized values appear in parallel with the values you'd compute otherwise.

[@EEE-iw3fk]

@@ElectronicswithProfessorFiore You are right. I just realized that. Thanks for the tip. I used the theorem on op-amp's a lot.

[@engineeringjoe]

Whats thename of the Spice Software

[@ElectronicswithProfessorFiore]

In the video, I am using TINA-TI, the free version of the TINA simulator that you can get from Texas Instruments.

[@davidluther3955]

WITHOUT THE SPICE PROGRAM HOW DO YOU GET THE Ic,Ib OR,DECIDE WHAT THE VALUE OF Ic VALUE SHOULD BE?

[@ElectronicswithProfessorFiore]

A proper answer is way beyond a simple comment here. I suggest watching the earlier videos in this playlist that cover BJTs as a start, and download my free textbook Semiconductor Devices.

[@davidluther3955]

EXCELLENT EXPLAINATION! WHY DID NOT USE A BYPASS CAPACITOR IN THIS CIRCIUT?