Revision Deck

Question 1

What is the notation you need to remember for small signal analysis?

Answer 1

Question 2

BJT: How should you connect a external voltage source to the EB junction of a transistor to enable forward bias?

Answer 2

You want to connect the positive terminal (high voltage) to the p-side and the negative terminal to the n-side. This goes for both npn and pnp.

Question 3

If there is no resistor connected to the emitter, what small signal model should you be using?

Answer 3

hybrid-pi

Question 4

What is the method of determining the gain of a CE amplifier that you need to remember

Answer 4

Steps are as follows:

V_sig -> i_b by multiplying by 1/(R_sig + r_in)

i_b -> i_c by multiplying by β

i_c -> v_o by multiplying by R_c

where R_c is the resistance in parallel with v_o

Question 5

Why are two different definitions for the gain, i.e. A_v and A_vo used to characterise amplifiers?

Answer 5

It is just convention to make it easier to deal with circuits when they get more complex

When you want to see how R_sig loads the device on its own, or how R_L loads the device.

Question 6

MOSFET: CS amplifier small signal model, Rin, Ro, Av, Gv ?

Answer 6

Av =Vo /Vi

Gv =Vo/Vsig

Question 7

MOSFET: CS amplifier with source resistance, small signal model, Rin, Ro, Av, Gv

Answer 7

𝐴_vo = 𝑔_𝑚𝑅_𝐷 / (1 + 𝑔_𝑚𝑅_s)

G_v = 𝑔_𝑚𝑅_𝐷 / (1 + 𝑔_𝑚𝑅_s)

Question 8

MOSFET: CG amplifier small signal model, Rin, Ro, Av, Gv

Answer 8

Question 9

MOSFET: CD amplifier (source follolwer) small signal model, Rin, Ro, Av, Gv

Answer 9

Look at the t-model it is just potential division.

Question 10

What do you need to remember about this thevenin question?

Answer 10

You need to do successive thevinin equivalent circuits.

Question 11

How do you apply Nortons Theorem?

Answer 11

Norton’s theorem is used to represent a part of network by a current source In and a parallel impedance Zn .

To determine In, short-circuit the two terminals of Network A and measure the current.

To determine Zn , reduce all external (i.e., independent) sources in Network A to zero by short-circuiting voltage sources and open-circuiting current sources. Then obtain the input impedance of Network A, Zn .

Question 12

Single-time-constant circuits

Answer 12

Single-time-constant (STC) circuits are those circuits that are composed of or can be reduced to one reactive component (inductance or capacitance) and one resistance.

𝜏 = 𝐿 / 𝑅

or

𝜏 = 𝐶𝑅

Question 13

time constant of the circuit

Answer 13

Question 14

Where does the maximum error comes from in the magnitude-response and phase-response plots for High Pass and Low Pass?

Answer 14

it comes from approximating two straight-line asymptotes (one of which is the slope).

For both High Pass and Low Pass the maximum error in the mangitude-response graphs is 3db

Similarly the maximum error in the phase response graphs is 5.7°

Question 15

Sketching Magnitude Response

Answer 15

Question 16

What sort of function is this?

Answer 16

First-order function of a LP

Question 17

What sort of function is this?

Answer 17

Question 18

What is a pole and what is a zero?

Answer 18

Poles are the coefficients associated to s-values in the denominator.

Zeros are coefficients associated to s-values in the numerator.

Question 19

A pole at s=a (a≠0) leads to a slope of what…

Answer 19

-45º/decade

and extends from 0.1|a| to 10|a|.

Remember that slope starts 0.1 before the pole value and finishes 10x after.

Question 20

Quickly determining the pole frequencies of CE amplifier?

Answer 20

Question 21

Last one

Answer 21

Question 22

Upper 3-dB frequency equation

i.e. the frequency of the dominant pole (if it exists…)

What happens if it doesn’t exist?

Answer 22

tau_H will equal the sum of tau’s multiplied by 2π

Question 23

In a CS Amplifier, do capacitors contribute poles or zeros?

Answer 23

poles

Question 24

How can you better estimate the 3-dB frequency even if the poles are far apart?

Answer 24

Question 25

What is the miller approximation?

What about millers theorem

Answer 25

Miller’s approximation is using the dominant pole to determine the 3dB frequency f_H.

The dominant pole is due to the capacitance at the input side.

Millers theorem, you take into account the effects of poles the 3dB frequency on the input and output side.

Question 26

Oscillators: What is the Barkhausen Criterion?

Answer 26

Question 27

Negative Feedback: What are the benefits of negative feedback?

Answer 27

1. Desensitize the gain. Gain is less sensitive to variations in values of circuit components.
2. Reduce nonlinear distortion. Keep output as linear as possible with respect to the input.
3. Reduce the effect of noise. Minimize the contribution from unwanted noise sources.
4. Control the input and output resistances. Raise or lower the input and output resistances by the selection of an appropriate feedback topology.
5. Extend the bandwidth of the amplifier.

Question 28

Negative Feedback: desensitivity factor

Answer 28

The percentage change in Af is smaller than the percentage change in A by a factor equal to the amount of feedback.

This factor is called the desensitivity factor, 1+Aβ

Question 29

Negative Feedback: What is the value of the feedback gain (β) for this ideal non-inverting amplifier?

Answer 29

Question 30

Negative Feedback: What is the Series – Shunt configuration used for?

Answer 30

When the output is a voltage source (RHS)

Question 31

Negative Feedback: What is the Series – Series configuration used for?

Answer 31

When the output is a current source (RHS)

Question 32

Negative Feedback: Configuration equations for Gain, Rin and Rout.

Answer 32

Question 33

Power Amplifiers: What determines the Power Amplifier classification

Answer 33

Classification depends on the placement of the Q-point (DC operating point).

Question 34

Power Amplifiers: What determines the conduction angle of Power Amplifiers

Answer 34

The Q-point (DC operating point).

Question 35

Oscillators: Phase-shift oscillator Transfer Function

Answer 35

Question 36

Power Amplifiers: Class AB

Answer 36

Question 37

Power Amplifiers: What is the symbol for average load power?

And total average supply power?

Answer 37

P_L

P_S