5.3 Data Conversion Flashcards
What are ADC and DAC used for?
Interface computers to the analogue world so that a computer can monitor and control a PHYSICAL variable.
What does the transducer do?
Converts physical variable into electrical variable.
What does the ADC do?
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.
What does the computer do?
Receives the digital input from the ADC, performs calculations or other operations , then outputs a digital value for the physical variable towards the DAC.
What is the purpose of the DAC?
Converts digital (001110000) to an proportional analogue VOLTAGE or CURRENT ( o-10 Volts), Sending this information to the physical variable (actuator).
What are OP AMPS used for?
Compare the amplitude of one voltage with another.
What are the characteristics of the IC Op AMP?
High gain, high input impedance, low output impedance, Used with split supply, Used with feedback, with gain determined by the feedback network.
How is a zero level detector hooked up?
With the inverting input directly grounded to produce a zero level, input signal to non inverting.
What else can the zero level detector be used for?
Used as a squaring circuit to produce a square wave from a sine wave.
Describe how the Zero level detector operates.
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).
Most OP AMPS have a maximum output voltage limitation of?
+/- 15 Volts because of their DC supply voltages.
How can the zero level detector be modified to detect voltages other than zero AKA Non-Zero Level Detection.
By connecting a fixed reference voltage to the inverting (-) input. By either a Battery, Voltage divider or a ZENER diode.
With a Non-Zero level Detector what conditions need to be met to reach maximum output positive voltage?
Input voltage must exceed reference voltage.
What is the definition of a true comparator?
Effectively compares 2 input voltages and delivers a output.
An OP AMP with an inverting amplifier with a gain of ONE serves as?
Inverting buffer
What are the disadvantages of a Flash A/D Converter?
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.
What are the disadvantages and advantages of the Flash A/D converter?
Too expensive but practical when very high speeds are required.
What is this the name of this unit?
Flash A/D Encoder
What is the make up of a Flash A/D Converter - Encoder?
A set of Exclusive-OR gates, and a matrix of diodes.
What are the advantages and disadvantages of the Flash A/D Converter Encoder?
Simplest operational theory, most efficient of the ADC technologies in terms of speed. Disadvantage = Most component intensive.
What is an additional advantage of the flash a/d encoder?
Can produce a scaled output.
How can you create a nonlinear response of the analogue input signal in a ADC
Resistor values in the voltage divider network are of different values.
With equal value resistors in the reference voltage divider network of a ADC what occurs?
Each successive binary count represents the same amount of analog signal increase.
What is this figure?
Digital ramp ADC
What resets the counter to zero on a Digital-Ramp ADC?
A start pulse is applied to reset the counter to zero.
What are the Advantages of a Digital Ramp ADC?
Much less expensive. fewer components.
What is a disadvantage of the Digital-Ramp ADC?
Slower
What components make up the Digital-Ramp ADC?
Single Comparator, Counter, DAC and a Control AND gate.
What else is the Digital-Ramp ADC referred as?
Counter type ADC.
What is this figure?
Binary Weighted Resistor D/A Converter and Truth Table.
What are the disadvantages of a Binary Weighted DAC
Large difference in resistor values, temperature varies resistance.
What are the advantages of a R2R ladder?
Only 2 resistance values not greatly different, temp variations have little effect.
The flash AD encoder circuit has a?
Nonlinear response to the analogue signal input.
Characteristics of a IC Op AMP
High gain, High input impedance, used with split supply, used with feedback with gain determined by feedback network.
What are the 2 basic methods of Analogue to Digital Conversion?
Flash/Simultaneous and Digital-Ramp/Counter type.
How many comparators does a 4 bit binary number require?
15 Comparators
How many comparators does a 8 bit circuit require?
255 comparators.
How many comparators does a 3 bit circuit rewuire?
7 comparators.
