Week 4

Question 1

What are the two inputs of a circuit symbol?

Answer 1

Two inputs – marked with minus (-) is the inverting input and the one marked with plus (+) is the non-inverting input

Question 2

What are the three parts of a circuit symbol?

Answer 2

• Two inputs – marked with minus (-) is the inverting input and the one marked with plus (+) is the non-inverting input
• One output
• Mainly, two power supplies, one positive and the other one negative.
  However, can also have a single power supply

Question 3

What is an ideal op-amp? (3)

Answer 3

• Input resistance Ri  ∞very large) making the current going into the op-amp zero
  - Output resistance Ro = 0
•  The gain Aod is very high leading to v1 = v2 for a finite output voltage v0

Question 4

What is a voltage follower (unity gain amplifier)?

Answer 4

In this case, the feedback resistor of the non-inverting amplifier 􏰝􏰔 is made zero (i.e., short circuited) and 􏰝􏰕is open circuited.

Question 5

Why is the voltage follower useful as? (2)

Answer 5

The voltage follower is very useful as an intermediate stage buffer (amplifier) in isolating one circuit from another
 It minimises interaction between the two stages and eliminates inter-stage loading

Question 6

What is a summing amplifier?

Answer 6

The summing amplifier is an op-amp circuit that combines several inputs and produces an output that is the weighted sum of the inputs

Question 7

What is a difference amplifier?

Answer 7

The difference amplifier is an op-amp circuit that amplifies the difference between two inputs but rejects any signals common to the two inputs

Question 8

What are the three regions that a BJT(Bipolar Junction Transistor) can operate in?

Answer 8

 Active
 Cut-off
 Saturation

Question 9

What are basic transistor operations? (2)

Answer 9

switch and amplifier

Question 10

How does a switch work when the transistor is cut off? (2)

Answer 10

 For 􏰁 􏰁􏰮􏰯 , the transistor is cut-off. So
that 􏰙􏰮 􏰏 􏰙􏰱 􏰏 0. Hence 􏰁􏰎 􏰏 􏰁􏰱􏰱 and the voltage across the load is zero.

 Since the currents in the transistor are zero, the power dissipation in the transistor is zero and the load would be cut-off with zero current.

Question 11

How does a switch work when the transistor is saturated?

Answer 11

If 􏰁􏰩 􏰷 􏰁􏰮􏰯 , and if the transistor is driven into saturation by making 􏰝􏰮 small compared to 􏰝􏰱, which is the effective resistance of the load

Question 12

What is an amplifier?

Answer 12

Transistors can be used to amplify a current or a voltage signal when they
operate in the active region