All Prior Quiz Prep sheets, homework, lectures, and reading assignments.
As always, you should be able to do all problems with either NPN or PNP transistors - know the difference!
Explain what a diode-connected BJT is and show that the equation governing it's I-V characteristic is the same as that of a diode and that it's incremental resistance is simply the transistor's emitter resistance.
Draw the basic current mirror circuit and explain how it achieves its current mirror behavior.
For each of the four current mirror configurations studied (basic, base-current compensated, Wilson, and Widlar) do the following:
1) Draw the circuit.
2) Determine the current transfer ratio of the mirror.
3) Determine the output resistance presented to its load.
4) Determine the input resistance presented to the circuit providing the reference current.
5) Determine the critical voltage at the output where the mirror quits behaving properly.
6) Explain how each of the improved current mirrors gets its improved performance relative to the basic current mirror. In other words, explain how the additional components improve the circuit.
7) If the transistors all have a beta of 100? How many transistors can the mirror drive (the basic circuit is driving one) before the current transfer ration falls to 90% of the reference current.
Determine the current transfer ratio for a given Widlar current source.
Determine the component sizes needed to achieve a desired current transfer ration in a Widlar current source.
What is an "active load"? What are the advantage of using one.
A given circuit might be intended for a discrete component implementation or it might be intended for an integrated circuit implementation. Describe some of the advantages and difficulties that designers face in each case.
In a discrete transistor current mirror (as an example) there is a phenomenon known as thermal runaway that can occur. What is this phenomenon, what is the mechanism that leads to it, and what are some of the techniques that can be used to prevent it?