3. Signal Conditioning

Question 1

5 properties of ideal op amps

Answer 1

infinite input resistance
zero output resistance
infinite open-loop gain
infinite bandwidth
resistance to other factors ie temperature, acceleration

Question 2

What is the virtual earth principle? include the condition for using this principle

Answer 2

condition: Open loop gain A is very large. Principle: The opamp does whatever is necessary to keep the input terminals at the same potential (as the potential difference of non-inverting input to inverting is so small there is effectively no potential difference).

Question 3

gain of an inverting amplifier

Answer 3

G = - R2/R1

where R2 is the feedback resistor, R1 is the Vin resistor

Question 4

what is the virtual earth of an inverting amplifier?

Answer 4

V(i), the inverting input (after the input resistor) as the non-inverting input is grounded and the potential difference between non-inverting and inverting input is assumed to be 0.

Question 5

What is the input resistance of the inverting amplifier?

Answer 5

it is equal to the resistance R1, the resistance connected to the inverting input.

Question 6

What is the main drawback of an inverting amplifier? (due to resistor topology)

Answer 6

We want R1, the input resistance to be as high as possible to reduce unnecessary heating, but this will reduce the gain (-R2/R1). Increasing R2 may cause the current to find other pathways in the op amp and screw it over.

Question 7

What is the input resistance of the non-inverting amplifier?

Answer 7

infinite

Question 8

gain of a non-inverting amplifier

Answer 8

(R1+R2)/R1, where R2 is the feedback resistor OR 1 + R2/R1