5.3 Data Conversion

Question 1

What are ADC and DAC used for?

Answer 1

Interface computers to the analogue world so that a computer can monitor and control a PHYSICAL variable.

Question 2

What does the transducer do?

Answer 2

Converts physical variable into electrical variable.

Question 3

What does the ADC do?

Answer 3

Receives an electrical analogue input from the transducer, converts it into a digital output consisting of a number of bits to represent that analogue value. (01010000 = 80mV) Then sends the information to the Computer.

Question 4

What does the computer do?

Answer 4

Receives the digital input from the ADC, performs calculations or other operations , then outputs a digital value for the physical variable towards the DAC.

Question 5

What is the purpose of the DAC?

Answer 5

Converts digital (001110000) to an proportional analogue VOLTAGE or CURRENT ( o-10 Volts), Sending this information to the physical variable (actuator).

Question 6

What are OP AMPS used for?

Answer 6

Compare the amplitude of one voltage with another.

Question 7

What are the characteristics of the IC Op AMP?

Answer 7

High gain, high input impedance, low output impedance, Used with split supply, Used with feedback, with gain determined by the feedback network.

Question 8

How is a zero level detector hooked up?

Answer 8

With the inverting input directly grounded to produce a zero level, input signal to non inverting.

Question 9

What else can the zero level detector be used for?

Answer 9

Used as a squaring circuit to produce a square wave from a sine wave.

Question 10

Describe how the Zero level detector operates.

Answer 10

Used to determine when an input exceeds a certain level, very small differences between the inputs causes the output to go into maximum (saturation/square waves).

Question 11

Most OP AMPS have a maximum output voltage limitation of?

Answer 11

+/- 15 Volts because of their DC supply voltages.

Question 12

How can the zero level detector be modified to detect voltages other than zero AKA Non-Zero Level Detection.

Answer 12

By connecting a fixed reference voltage to the inverting (-) input. By either a Battery, Voltage divider or a ZENER diode.

Question 13

With a Non-Zero level Detector what conditions need to be met to reach maximum output positive voltage?

Answer 13

Input voltage must exceed reference voltage.

Question 14

What is the definition of a true comparator?

Answer 14

Effectively compares 2 input voltages and delivers a output.

Question 15

An OP AMP with an inverting amplifier with a gain of ONE serves as?

Answer 15

Inverting buffer

Question 16

What are the disadvantages of a Flash A/D Converter?

Answer 16

The number of comparators in the circuit increases exponentially with the number of binary bits. eg: a 4-bit binary number counting from 0 to 15 requires 15 comparators. An 8 bit circuit would require 255 comparators, too expensive for ordinary use.

Question 17

What are the disadvantages and advantages of the Flash A/D converter?

Answer 17

Too expensive but practical when very high speeds are required.

Question 18

What is this the name of this unit?

Answer 18

Flash A/D Encoder

Question 19

What is the make up of a Flash A/D Converter - Encoder?

Answer 19

A set of Exclusive-OR gates, and a matrix of diodes.

Question 20

What are the advantages and disadvantages of the Flash A/D Converter Encoder?

Answer 20

Simplest operational theory, most efficient of the ADC technologies in terms of speed. Disadvantage = Most component intensive.

Question 21

What is an additional advantage of the flash a/d encoder?

Answer 21

Can produce a scaled output.

Question 22

How can you create a nonlinear response of the analogue input signal in a ADC

Answer 22

Resistor values in the voltage divider network are of different values.

Question 23

With equal value resistors in the reference voltage divider network of a ADC what occurs?

Answer 23

Each successive binary count represents the same amount of analog signal increase.

Question 24

What is this figure?

Answer 24

Digital ramp ADC

Question 25

What resets the counter to zero on a Digital-Ramp ADC?

Answer 25

A start pulse is applied to reset the counter to zero.

Question 26

What are the Advantages of a Digital Ramp ADC?

Answer 26

Much less expensive. fewer components.

Question 27

What is a disadvantage of the Digital-Ramp ADC?

Answer 27

Slower

Question 28

What components make up the Digital-Ramp ADC?

Answer 28

Single Comparator, Counter, DAC and a Control AND gate.

Question 29

What else is the Digital-Ramp ADC referred as?

Answer 29

Counter type ADC.

Question 30

What is this figure?

Answer 30

Binary Weighted Resistor D/A Converter and Truth Table.

Question 31

What are the disadvantages of a Binary Weighted DAC

Answer 31

Large difference in resistor values, temperature varies resistance.

Question 32

What are the advantages of a R2R ladder?

Answer 32

Only 2 resistance values not greatly different, temp variations have little effect.

Question 33

The flash AD encoder circuit has a?

Answer 33

Nonlinear response to the analogue signal input.

Question 34

Characteristics of a IC Op AMP

Answer 34

High gain, High input impedance, used with split supply, used with feedback with gain determined by feedback network.

Question 35

What are the 2 basic methods of Analogue to Digital Conversion?

Answer 35

Flash/Simultaneous and Digital-Ramp/Counter type.

Question 36

How many comparators does a 4 bit binary number require?

Answer 36

15 Comparators

Question 37

How many comparators does a 8 bit circuit require?

Answer 37

255 comparators.

Question 38

How many comparators does a 3 bit circuit rewuire?

Answer 38

7 comparators.