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ELEC 2130 Electronic Circuit Design > Term 1 Test > Flashcards

Term 1 Test Flashcards

1
Q

Definition of: Transducer
Sensor
Signal Conditioning

A

T: Converts energy from one form to another
S: device (typically transducer) that is used to convert various physical quantities to electrical signals
SC: collection of circuit functions that process a signal in order to change one or more properties (amplitude, frequency etc)

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2
Q

Examples of signal conditioning functions-7 in total
A Bat Flew Down Into BUs
and then Vanished

A 
Amplification/Attenuation
Buffering/Impedance
Filtering
DC offset correction
Isolation
Balenced to Unbalenced Conversion
Voltage/Current conversion
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3
Q 
Amplification/Attenutation:
What do each do
What kind of circuit is needed to do this
What is amplification often used for
What is attenuation often used for
A

Increasing/decreasing the power of a signal
An active circuit is needed
Amping up signals from sensors that produce weak outputs
Reducing signals that are too large to be processed properly

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4
Q

Buffering/Impedance matching:
What are they
When are they used

A

Buffer: op amp where input impedance is very high, output impedance is very low and gain is unity.
Prevents one stage from loading the next
Impedance matching: using an op amp to present a specified input/output impedance
Needed when two stages in a circuit need different impedances

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5
Q

Filtering: just definition

A

Seperation of signals on the basis of their frequency content

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6
Q

DC offset correction: what does it do

Example of when it is useful

A

Adding or removing DC offset from an AC signal

When using an ADC converter as input voltage must be completely positive

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7
Q

Isolation: what is it

Why would you use it

A

Isolating a signal electrically
ALthough there is an output signal there is no electrical current path between input and output
For safety or to protect components from damaging voltage

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8
Q

Balanced to Unbalanced Conversion: how does it work

A

Converts two conductors to a differential system

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9
Q

Voltage/Current conversion:
whys this useful
How to do it for large currents

A

Many sensors produce a current as output, but its generally more convenient to process the signal as a voltage
Pass the current through a low resistance

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10
Q

Circuit diagram vs system diagram

A

CD: contains topology of circuit component connections, drawn schematically
SD: concerned with relationships between functional blocks within a system

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11
Q

System concept diagram vs system module diagram

A

SCD: not as detailed, tells you how a system operates
SMD: detailed, tells you how real sub-system parts are connected (included signal types, power levels etc)

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12
Q

Op-amps:
Vout equation
Ideal op amp characteristics

A 
Vout = A(V+ - V-)
A = gain
V+/V- = non-inverting and inverting inputs

A is infinite
Input impedance is infinite
Output impedance is zero

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13
Q

Non-inverting op amp:
What does it look like
Whats the gain equation

A

Vin = V+
V- : potential dividor between Vout and ground
G = 1 + R2/R1
R2 is top resistor, R1 is bottom

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14
Q

Inverting op amp:
What does it look like
Whats the gain equation

A

V+ = ground
V- = Vin through a resistor (R1)
R2 goes between Vout and between R1 and V-
G = -R2/R1

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15
Q

Op-amp limitations: input and output limits

A

Input limits: there is a max voltage difference that can be applied between V+ and V-
Output limit: output voltage cannot exceed power supply voltages

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16
Q

Op-amp limitations: unwanted phase shift

A

Each RC network in an op amp can cause unwanted phase shift.
Each network has 6dB/octave or 20dB/decade roll-off and -90 phase shift
If total phase shift is 180, we get positive feedback

17
Q

Op-amp limitations: how to solve unwanted phase shift

A

Theres a purpose built rc circuit that rolls off sooner to have a more controlled roll off and max of 90 phase shift

18
Q

Op-amps: removing DC components

A

Use capacitor before first resistor and the formula F = 1/(2πCR)

19
Q

Op-amps: impedance matching for non-inverting op amp (Vin = V+)

A

Input: resister in parallel with Vin, Sets impedance
Output: Resistor in series
Remember about potential dividor

20
Q

Op-amps: impedance matching for inverting op amp (V+ = ground)

A

Input: R1 = input impedance
Output: Resistor in series
Remember about potential dividor

21
Q

Op amps: creating a buffer with non-inverting and inverting op amps

A

Non-inverting: connect Vout to V- without any resistors

Inverting: set R2 = R1

22
Q

Op amps: get attenuation

A

Use a potential dividor into a buffer to avoid high output impedance

23
Q

What is slew rate?

Whats the value of slew rate needed for undistorted output?

A

How quickly an op-amp can change its output voltage
Aω (V/s)
A = peak amplitude
ω = frequency

24
Q

Biasing input currents:
Why is this needed?
How do you do it?
What do you need to watch out for>

A

As op amp input impedance isn’t infinite so a small current will flow.
If you have a capacitor at the input, it will accumulate charge.
To solve this place a resistor in parallel going to ground.
Watch out-this forms a high pass filter

25
Q

Input offset voltage:
Why does it happen?
How do you fix it

A

An ideal op amp shouldn’t output voltage if the difference between two inputs is the same.
However in practise there is a small internal offset voltage
Most op-amps include a potentiometer to compensate for it

26
Q

Common-Mode Rejection Ratio equations-2 types and last one in μV/V and dB

A 
CMRR = 20*log(Adiff/Acom) (db)
Adiff = differential voltage gain
Acom = common-mode voltage gain
CMRR = ΔVdiff/ΔVcom
CMRR = -20*log(ΔVdiff/ΔVcom)
V = voltage signals required to obtain the same change in output voltage
27
Q

Power Supply Rejection Raito:
What is it
Two equations for it, in μV/V and dB

A

The extent to which the op-amp rejects fluctuations on the power supply rails
PSRR = ΔVdiff/ΔVPSU (μV/V)
PSRR = -20*log(ΔVdiff/ΔVPSU)

28
Q

5 things to consider when choosing op-amps

A 
General purpose (price, easy to use)
High speed (high frequency)
Precision (low offsets, high CMRR)
Low power (low standby power consumption)
Low noise
29
Q

How to create a Wheatstone Bridge circuit to get two differential voltages when using a sensor

A

Diamond shape-Vsupply at top and ground at bottom
Two resistors on top two sides
Balance resistor on one side and sensor on the other
Voltage points are on the points on the left and right

30
Q

Filter characteristics for n-pole filters-4 types
BBCE
What do the graphs look like

A

Bessel: Flat start, shallow roll off
Butterworth: flat start, less shallow roll-off
Chebyshev: has wavy start, steep roll-off
Elliptic: has wavy start and finish, steepest roll off

31
Q

Low pass and high pass circuits-both for RC and LC circuits

A

Low-pass: RC and LC

High-pass: CR and CL

32
Q

What does a Sallen-Key filter look like?
Use low pass for example
How to do a high pass?

A

Combination of inverting and non-inverting op-amps.
Potential dividors into V- (RA/B)
Resistors in series into V+ (R1/2)
Capacitor 1 between Vout and between R1 and R2
C2 goes to ground from between R2 and V+
Swap R1 and C1 etc for high pass

33
Q

Designing a Sallen-Key filter
What values to choose?
What formulas to choose for butterworth and Chebyshev (RC = …)

A 
R1 = R2
C1 = C2
Use RA and RB in the non-inverting formula K = 1 + RA/RB
And get K from the table
B: RC = 1/ω0 
C: RC = 1/ω0*Cn
Cn = normalising factor
34
Q

Using a op-amp for current to voltage conversion

Whats the formula for Vout for both types?

A

Inverting Op amp except instead of the first resistor you put a diode facing either away from ground or towards a voltage rail
Ground: Vout = RId
Rail: Vout = -RId

35
Q

Schmitt trigger:
What does it do?
What does it look like?
How to solve?

A

Detects when the input signal has crossed a certain threshold
Vin = V-
Vout connects to a potential dividor through resistor 3.
V+ = the gap between R3 and the potential dividor
Ask Henry

36
Q

Peak detector:
What does it do?
What does it look like?

A

Detects max amplitude or peak of a AC wave
Vin = V+
Vout goes through a diode before splitting into 3.
One goes to V-
One goes to ground through a capacitor
One goes to Vout

37
Q

For an n-bit ADC how many levels does it have?
What is sampling?
What is quantisation?

A

2^n levels
S: Recording the amplitude of a signal at specifc
Q: asigning a sample to one of a fixed number of amplitude values

38
Q

ADC definitions:
What is Full Scale Value
What is Full Scale Range
What is resolution

A

FSV: High quantisation level
FSR: difference between highest and lowest quantisation levels
Resolution: number of different quantisation levels we have

39
Q

Using ADC’s with microcontrollers: 3 things to remember

A
  1. ADC range is always positive
  2. FSV determined by MC max voltage input
  3. Most microcontrollers have a maximum source resistance

ELEC 2130 Electronic Circuit Design (2 decks)

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