Due Monday 2018-02-19 at the end of class.

1. Reading

Read / review [AoE] section 2.3 up until section 2.3.8 Differential amplifiers (our next topic).

Here are some notes on how the content of that section maps to our current course location:

  • Earlier, in section 2.2.9, is the concept of transconductance.

  • Section 2.3.2 starts with some ratio rules. Since they are at the page break, they are easy to miss, but are important for quickly understanding a circuit. BJT Rules of thumb has more discussion of these. Here are some (notice the capitalization means DC values):

    • \(\dfrac{I_{C2}}{I_{C1}} = \exp\left(\dfrac{\Delta V_{BE}}{V_T}\right)\)

    • \(\Delta V_{BE} = V_T \ln\left( \dfrac{I_{C2}}{I_{C1}} \right)\)

  • If you were paying attention, the Lab 3B circuit demonstrated a large temperature dependence in the Q3 collector current when adding L1. Section 2.3.2.C speaks to this effect.

  • Section 2.3.2.D (p. 92) is Early effect, modelled as \(r_o\) in the transistor small-signal models.

  • The circuits of section 2.3.5 (p 96-) should be familiar!

  • Section 2.3.6 about the perfect transistor may be interesting. Such a structure (or rather voltage-in and current-out) is usually called an operational transconductance amplifier or OTA. They are quite common in analog integrated circuits (on-chip), and not as common for circuit-board level electronics.

2. Study

Slowly read through the Minima microphone amplifier analysis from [341-notes] that was started in class Wednesday.

It has complete worked solutions for the:

  • DC bias solution

  • Small-signal voltage gain Av

  • Small-signal input impedance Rin and Zin

  • Small-signal output impedance Rout and Zout

Most important is to make the connections between the full-on algebra and the table entries of [bjt-amplifiers#bjt-amplifiers].

3. Lab circuit analysis

Use Minima microphone amplifier analysis as your example of how your work should look in terms of neatness and format.

Clearly write out your mathematical circuit analysis of the following for your specific lab circuit and power supplies, in all cases, ignore \(r_o\) by replacing it with an open circuit:

  • DC bias solution. All node voltages and collector currents.

  • Amplifier input resistance, \(R_{in}\), not just the CE amplifier’s \(Z_{in}\) from the Table. (Lab 3A: with Ce but not L1), (Lab 3B: without L1)

  • Amplifier voltage gain \(v_{out} / v_{in}\).

  • Estimate your amplifier’s output resistance \(R_{out}\), again not merely the CE amplifier’s \(Z_{out}\).

Turn in this work at the end of class on Monday.

4. References