Lecture #5 - Non-Linear Devices

Question 1

Give an example of a linear and non-linear device

Answer 1

Linear; Resistor
Non-linear; diode

Question 2

A general nonlinear device can be modelled through a TS; what is the equation and what’s the significance of which the coefficient holds dominance

Question 3

When is nonlinearity desirable and not desirable?

Question 4

What is the characteristics of the practical equation for gain

Answer 4

1. The gain is less than an ideal amplifier.
2. There’s a dependance on V_0

Question 5

What does the spectrum look like for an ideal amplifier

Answer 5

A straight line centred around f_0

Question 6

For a real amplifier, what happens to the output power

Answer 6

The actual power drops by 1db; which is called the 1db compression point.

Question 7

What happens when a single sinusoid (one tone) of frequency w_o is input into a non-linear device.

Answer 7

Its output signal consists of multiple frequencies

Question 8

Are harmonics desired or undesired in a device?

Answer 8

It depends; undesired in an amplifier, good for frequency multiplier or sub-harmonic mixer.

Question 9

What is the noise floor?

Answer 9

It’s the amount of noise that the frequency signal (RF) must be stronger to be detected.

A higher noise floor indicates a lower sensitivity within the system.

Question 10

What is the fundamental tone?

Question 11

What are the intermodulation products

Answer 11

The addition and reduction of sinusoid tones in the frequency

Question 12

In a signal, what are we only interested in amplifying?

Answer 12

cosw_1t

Question 13

What happens when a bass pand filter can’t filter out the third-order intermodulation products

Answer 13

1. This leaks into the different

Question 14

What is the IP3 or the TOI value

Question 15

Why do we need an IP3, if it’s hypothetical?

Answer 15

The IP3 value indicates how large of a signal the amplifier can process before Intromodulation Distortion (IMD) occurs.

A high IP3 value implies that the device has good linearity, whereas, a low IP3 value means the intermodulation products could interfere with the fundamental signal.

Question 16

Explain the practical measurement of the IP3 point.

Question 17

Are intermodulation products deterministic or stochastic?

Answer 17

Deterministic

Question 18

In the output IP3 point of a three stage cascaded system, what happens when one one of the OIP3 values are low?

Answer 18

This dominates the value

Question 19

What happens when of the the OIP3 values is out of phase?

Answer 19

It lowers the overall OPI3 value

Question 20

The IP3 point is usually given in terms of what?

Answer 20

In terms of the higher power.

Amplifier OIP3
Mixer IP3

Question 21

Explain the relationship between noise and OIP3

Answer 21

An ideal Rx requires the lowest NF and the highest OIP3, but these requirements are often contradictory and a trade-off is needed in a system design.

Question 22

Which is more important IP2 or IP3?

Answer 22

IP3 and in general odd-order IMD are closer to the fundamental tones, hence they are of a bigger concern in components whose desired output has the same frequency as its input

Question 23

Give a layman’s example of Desensitization

Answer 23

If you’re listening to somebody, but there is one person shouting in your ear and the other person is whispering.

Person who is whispering is your desired signal. The person who is shouting is the interrupted signal.

That is essentially Desensitization.