ADC & DAC

Question 1

is the process by which analog signals are converted to their digitized forms.

Answer 1

ANALOG TO DIGITAL CONVERSION

Question 2

ADC steps

Answer 2

1. SAMPLING
2. QUANTIZATION
3. ENCODING

Question 3

The analog signal is sampled at regular intervals of time

Answer 3

SAMPLING

Question 4

The sampling rate must be at least twice the highest frequency of the signal

Answer 4

Nyquist Criterion

Question 5

It is defined as the process of converting the continuous sample amplitude into a discrete amplitude.

Answer 5

QUANTIZATION

Question 6

QUANTIZATION is defined as the process of converting the continuous sample amplitude into a discrete amplitude. Thus by then, the signal will be discrete in both: ____ and ____.

Answer 6

time and amplitude

Question 7

The difference between the actual analog value and quantized digit value.

Answer 7

QUANTIZATION ERROR

Question 7

It is the process which assigns ones and zeros (stream of bits) for every quantization level

Answer 7

ENCODING

Question 8

The number of bits assigned for each level (n) in ENCODING depends on the levels’ number (L); such that ____

Answer 8

L=2^n

Question 9

In an ideal analog-to-digital converter, the quantization error is uniformly distributed between ____ and ___.

Answer 9

–Δ/2 and Δ/2

Question 9

The resolution of the ADC is the smallest detectable change in voltage.

Answer 9

IDEAL ADC

Question 10

Q = Δ = ____ (i) = ____ (ii)

Answer 10

i. quantization step
ii. full scale/level’s number

Question 11

TYPES OF ADCs

Answer 11

1. Direct conversion ADC
2. Successive approximation register (SAR) ADC
3. Integrating ADCs: single slope, dual slop, and ramp ADC
4. Sigma-Delta ADC (over sampled ADC)

Question 12

• It is one of the most popular ADCs for 8-16 bits
• It has moderate conversion speeds. The conversion time is around 1µs.
• It doesn’t consume a lot of power and its cost is low in comparison with the other types.
• It requires a sample, hold circuit, and it can have missing output codes.

Answer 12

SAR ADC

Question 13

A _______ works by using a digital to analog converter (DAC) and a comparator to perform a binary search to find the input voltage.

Answer 13

Successive Approximation ADC

Question 14

A _____ is used to sample the analog input voltage and hold (e.g. keep a non-charging copy) the sampled value whilst the binary search is performed.

Answer 14

Sample and Hold circuit (S&H)

Question 15

The _____ (i) starts with the most significant bit (MSB) and works towards the least significant bit (LSB). For an ________ (ii), 8 comparisons are needed in the binary search, taking a least 8 cycles.

Answer 15

i.binary search
ii. 8-bit output resolution

Question 16

The sample and hold circuit samples the analog input on a rising edge of the sample signal. The comparator output is a _____ (i) if the sampled analog voltage is greater than the output of the DAC, ___ (ii) otherwise.

Answer 16

i. logic 1
ii. 0

Question 17

Is the device which converts digital signals to analog ones.

Answer 17

DIGITAL TO ANALOG CONVERSION (DAC)

Question 18

Most of DACs consist of a network of ____ (i) and _____.

Answer 18

i. resistors
ii. analog switches

Question 19

DAC
The ______ control the currents or voltages that are derived from a particular reference voltage and provide analog output current.

Answer 19

switches

Question 20

TYPES OF DACs

Answer 20

1. Weighted resistor DAC
2. R-2R DAC
3. General purpose DAC (DAC 0800)
4. Frequency to voltage converter
5. Pulse width modulation

Question 21

TYPES OF ADC ERRORS

Answer 21

1. Offset Error
2. Gain Error
3. Nonlinearity Error
4. Temperature-dependent Error
5. Load-dependent Error
6. Hysteresis Error
7. Resolution Error
8. Missing code Error

Question 22

Constant component of the error that is independent of the inputs

Answer 22

OFFSET ERROR

Question 23

• Difference between the actual transfer ratio and the ideal ratio
• It is also called CALIBRATION ERROR

Answer 23

GAIN ERROR

Question 24

The deviation of the output quantity from a specified linear reference

Answer 24

NONLINEARITY ERROR

Question 25

Worst-case deviation from the ideal transfer characteristic curve

Answer 25

INTEGRAL NONLINEARITY

Question 26

Difference between the actual transfer ratio and the ideal ratio

Answer 26

DIFFERENTIAL NONLIEARITY

Question 27

Change in ambient temperature or temperature variation due to self-heating (temperature stability, temperature coefficient)

Answer 27

TEMPERATURE-DEPENDENT ERROR

Question 28

Is due to the effect of a load impedance upon the converter or signal source driving it.

Answer 28

LOAD ERROR

Question 29

The difference between the increasing and decreasing input values that produce the same output

Answer 29

HYSTERESIS ERROR

Question 30

The error due to the inability to respond to change of a variable smaller than a given increment

Answer 30

RESOLUTION ERROR

Question 31

In R-2R, the highest resistance value is ___ (i) and thus requires an area inside the IC ____ (ii) than that of the weighted resistor DAC which highest resistance is ___ (iii).

Answer 31

i. 2R
ii. less 8 times
iii. 16R

Question 32

In R-2R, the DAC analog output is represented by _______.

Answer 32

current

Question 33

An _______ is needed to convert the current to voltage level.

Answer 33

operational amplifier

Question 34

It is an 8-bit DAC with 16 pins IC.

Answer 34

GENERAL PURPOSE (DAC 0800)

Question 35

What is the conversion time of a General Purpose DAC?

Answer 35

100ns