Chapter 14: Data Conversion

Question 0

What type of switching device do most analog switches utilize.

Answer 0

Most analog switches use MOSFETs as the switching device.

Question 1

What are the three types of analog switches.

Answer 1

The three types of analog switches are single pole single throw, single pole double throw, and double pole single throw.

Question 2

What is multiplexing?

Answer 2

Multiplexing is a technique used in data acquisition systems where inputs from several different sources must be independently converted to digital form for processing.

Question 3

What is the basic configuration of a multiplexer?

Answer 3

A multiplexor is basically a series of independent switches with a common output.

Question 4

What is the purpose of an analog switch?

Answer 4

The purpose of an analog switch is to turn a signal off and on electronically.

Question 5

What components make a sample and hold circuit?

Answer 5

Sample and hold circuits consist of an analog switch,a capacitor, and input and output buffer amplifiers

Question 6

What is aperture time?

Answer 6

Aperture time is the time for the analog switch to fully open after the control voltage switches from its sample level to its hold level.

Question 7

What is aperture jitter?

Answer 7

Aperture jitter is the uncertainty in the aperture time?

Question 8

What is acquisition time?

Answer 8

Acquisition time is the time required for the device to reach its final value when the control voltage switches from its hold level to its sample level.

Question 9

What is droop?

Answer 9

Droop is the change in voltage from the sampled value during the hold interval because of charge leaking off of the hold capacitor.

Question 10

What is feedthrough?

Answer 10

Feedthrough is the component of the output voltage that follows the input signal after the analog switch is open.

Question 11

What is a digital to analog converter?

Answer 11

A digital to analog converter is device in which information in a digital form is converted to the analog form.

Question 12

What is a binary weighted input digital to analog converter?

Answer 12

The binary weighted input DAC uses a resistor network with resistance values that represent the binary weights of the input bits of the digital code.

Question 13

What is resolution?

Answer 13

The resolution of a DAC is the reciprocal of the maximum number of discrete steps in the output. 1/(2^n-1 )(100)where n is the number of steps. 4-bit= 1/((2^4)-1)(100)= 1/15(100)=6.6%

Question 14

What is accuracy?

Answer 14

Accuracy is a comparison of the actual output of the DAC with the expected output

Question 15

What is linearity?

Answer 15

A linear error is a deviation from the ideal straight-line output of the DAC.

Question 16

What is monotonicity?

Answer 16

A DAC is monotonic if it does not miss any steps when it is sequenced over its entire range of input bits.

Question 17

What is the disadvantage of the DAC with binary weighted inputs?

Answer 17

One of the disadvantages of this type of DAC is the number of different resistor values?

Question 18

What is the resolution of a four bit DAC?

Answer 18

1/((2^4)-1)(100)= (1/15)(100)=6.6%

Question 19

What is the advantage of a monolithic IC over a discrete circuit for an R/2R ladder.

Answer 19

Constructing the ladder network and monolithic IC provides much better matching of the R and 2R.

Question 20

What is settling time?

Answer 20

Settling time is normally defined as the time it takes a DAC to settle within half of it’s least significant bit of its final value when A change occurs in the input code.

Question 21

What is conversion time?

Answer 21

Conversion time is the time it takes an ADC to convert an analog waveform to a digital quantity.

Question 22

What is the Nyquist rate?

Answer 22

The Nyquist rate or sampling rate is the minimum sample rate and it must be greater than twice the maximum frequency component of the analog signal.

Question 23

What is quantization error.

Answer 23

Quantization error is error introduced when an analog signal changes during conversion time.

Question 24

How does a sample and hold circuit avoid quantization error in A/D conversion?

Answer 24

A sample and hold circuit allows an analog to digital converter to convert a constant voltage.

Question 25

What components does the stairstep ramp method use?

Answer 25

It employs a DAC and a binary counter to generate the digital value of an analog input.

Question 26

What component does the tracking method use?

Answer 26

The tracking method uses an up-and-down counter.

Question 27

What components does the single slope method use?

Answer 27

It uses a linear Ramp generator to produce a constant slope reference voltage. (No counter)

Question 28

What components does a dual slope method use?

Answer 28

A dual slope is similar to a single slope except that a variable slope and a fixed slope ramp are both used together?

Question 29

What components does the successive approximation method use?

Answer 29

The successive approximation ADC consist of a DAC, a comparator, and a successive approximation register.

Question 30

How does the successive approximation method work?

Answer 30

The bits of the DAC are enabled one at a time starting with the most significant bit. As each bit is enabled the comparator produces an output that indicates whether the analog input voltage is greater or less than the output of the DAC. If the DAC output is greater the register is reset. If the DAC output is less the bit is retained in the register.

Question 31

What are the advantages of the successive approximation method?

Answer 31

The successive approximation method is fast and uses the same number of steps every time?

Question 32

What is the fastest method of analog-to-digital conversion?

Answer 32

The flash or simultaneous analog-to-digital converter is the fastest.

Question 33

Which analog-to-digital conversion method uses an up-and-down counter?

Answer 33

The tracking method analog-to-digital converter uses an up/ down counter.

Question 34

The successive approximation converter has a fixed conversion time. true or false?

Answer 34

True

Question 35

What is the basic premise of a voltage to frequency converter?

Answer 35

An analog voltage on the input is converted to a pulse signal with a frequency that is directly proportional to the amplitude of the input voltage.

Question 36

What is non-monotonicity?

Answer 36

Nonmonotonicity is indicated by step reversals in an output ramp. This condition is usually caused by one of the binary input bits being stuck at a constant high or low state.

Question 37

What is differential nonlinearity?

Answer 37

Differential nonlinearity is a condition in which the step amplitude is less than it should be for certain input codes.

Question 38

What is offset error?

Answer 38

Offset error is when the step amplitude is greater or less than it should be for all input codes.

Question 39

What condition does low or high gain cause?

Answer 39

Hi or low gain will cause the output ramp to be steeper or more shallow than it should be.

Question 40

What does the typical voltage to frequency converter contain?

Answer 40

The typical voltage to frequency converter contains an integrator A comparator and a one shot.