AN100 PDF даташит
Спецификация AN100 изготовлена «Philips» и имеет функцию, называемую «An Overview if Data Converters». |
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Детали детали
Номер произв | AN100 |
Описание | An Overview if Data Converters |
Производители | Philips |
логотип |
6 Pages
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LINEAR PRODUCTS
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AN100
An overview of data converters
December 1991
Philips Semiconductors
No Preview Available ! |
Philips Semiconductors
An overview of data converters
Application note
AN100
INTRODUCTION
Large systems are comprised of many different subsystems, all of
which must interface to complete the system. All types of circuits,
including linear, digital and discrete, are often used in the
subsystems.
Interface circuits provide the necessary function of tying the parts of
a system together. These circuits are usually not purely linear or
digital but contain both types of circuit functions. For instance, sense
amplifiers are designed for interface between low level memory
outputs and bipolar levels, while differential comparators are
designed for interface between analog systems and logic systems.
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CONVERTERS
Digital communications, digital instruments and displays
have created a demand for low cost reliable converters. Key
factors in this demand are:
• The need to communicate with digital computers and equipment
for processing and storage of analog signals.
• Severe limitations encountered in reliable analog data
transmission over any considerable distance.
• The need for more easily readable displays.
General application areas for converters include: Data processing,
data transmission, graphics and displays, audio systems, control
systems and arithmetic operations.
SPECIFIC APPLICATIONS
Test Systems
• Transistor tester (Force IB and IC)
• Resistor matching
• Programmable power supplies
• Programmable pulse generators
• Programmable current source
• Function generators (ROM drive)
Arithmetic Operations
• Analog division by a digital word
• Analog quotient of 2 digital words
• Analog product of 2 digital words – squaring
• Addition and subtraction with analog output
• Magnitude comparison of 2 digital words
• Digital quotient of 2 analog variables
• Arithmetic operations with words from different logic families
Graphics and Displays
• Polar-to-rectangular conversion
• CRT character generation
• Chart recorder driver
• CRT displays
Data Transmission
• Modem transmitter
• Differential line driver
• Party line multiplexing of analog signals
• Multilevel 2-wire data transmission
• Secure communications (constant power dissipation)
Control Systems
• Reference level generator for set-point controllers
• Positive peak detector
• Negative peak detector
• Disc drive head positioner
• Microfilm head positioner
Audio Systems
• Digital AVC and reverberation
• Music distribution
• Organ tone generator
• Audio tracking A/D
• Speech compression and expansion
• Audio digitizing and decoding
DIGITAL
WORD
INPUT
ANALOG
D/A OUTPUT
REF
NOTES:
Output = Ref. x digital word
ǒ ǓB1 B2
BN
Output + Ref. x 2 ) 4 ) AAA ) 2N
SL00665
Figure 1. Conversion of a Digitally Coded Signal Input Into an
Analog Signal Output
–VREF
I0
I4 8R I3 4R I2 2R I1 R RF
–
+
VOUT
SL00666
Figure 2. Binary-Weighted Ladder Employing Voltage
Switching
1991 Dec
2
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Philips Semiconductors
An overview of data converters
Application note
AN100
DAC Building Blocks
The actual implementation of a D/A system contains four separate
parts: A reference quantity; a set of binary switches to simulate
binary coefficients B1 . . . BN; a weighting network; and an output
summing means.
IOUT
–VBIAS
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I1
IREF
2R I2 2R I3
RR
2R I4
R
I4 2R
V–
ǒ ǓNOTE:
IOUT + IREF x
b2 b3 b4
b1 ) 2 ) 4 ) 8
SL00667
Figure 3. R-2R Ladder Network Employing Current Switching
Binary-Weighted Ladder Employing Voltage
Switching
The disadvantages of a binary-weighted ladder employing voltage
switching include: a wide range of resistor values which are used in
weighting the network, and nodal capacitances which are
charged/discharged during conversion (See Figure 2).
EO
1 LIMIT
t
0
SETTLING
TIME
ÉÉÉÉÉÉÉFigure 4. Settling Time
ÉÉÉÉÉÉÉEO
10
ÉÉÉÉÉÉÉ8
ÉÉÉÉÉÉÉ6
ÉÉÉÉÉÉÉ5 ∆ EO ALL O’s ∆ O
ÉÉÉÉÉÉÉ4
ÉÉÉÉÉÉÉÉ0
000 001 010 011 100 101 110 111
ÉÉÉÉÉÉÉÉE
DIGITAL
INPUT
SL00668
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ SL00669
Figure 5. Offset Error
R-2R Ladder Network Employing Current
Switching
The advantages of this type of network include: no need for a wide
range of resistor values, and current switching eliminates
transients in nodal parasite capacitances (See Figure 3).
KEY SPECIFICATIONS
Speed
ÉÉÉÉÉÉÉThe conversion process should represent the input signal with the
highest fidelity and minimal lag in time (real-time applications).
ÉÉÉÉÉÉÉEO
ÉÉÉÉÉÉÉ10
ÉÉÉÉÉÉÉ8
ÉÉÉÉÉÉÉ6
ÉÉÉÉÉÉÉ4 ∆K
ÉÉÉÉÉÉÉ2
ÉÉÉÉÉÉÉÉ000 001
DIGITAL
INPUT
010 011 100 101 110 111
ÉÉÉÉÉÉÉÉE
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ SL00670
Figure 6. Gain Error
ANALOG
OUTPUT
F.S.
IDEAL
LINEARITY
ERROR
NON–IDEAL
0000 111 1
0011 001 1
0101 000 1
DIGITAL
INPUT
Figure 7. Relative Accuracy
SL00671
Settling Time
Settling time is a measure of a converter’s speed and is defined as
the elapsed time after a code transition for DAC output to reach final
value within specified limits, usually ± LSB (See Figure 4).
Errors
Offset Error – The output current or voltage of a DAC with zero
code input. (See Figure 5). Offset can and usually is trimmed to
zero with an offset zero adjust circuit.
Gain Error – Deviation in output voltage from correct level when the
input calls for a full-scale output. This error may be trimmed to zero
(See Figure 6).
Relative Accuracy – The maximum deviation of the DAC output
relative to an ideal straight line drawn from zero scale to full-scale
(See Figure 7).
Differential Non-Linearity – Incremental error from any ideal LSB
analog output change when the digital input is changed 1 LSB (See
Figure 9).
Monotonicity – As the input code is incremented from one code to
the next in sequence, the analog output will either increase or
remain constant (See Figure 9).
Stability
Stability is a measure of the independence of converter parameters
with respect to variations in external conditions such as temperature
and supply voltage.
1991 Dec
3
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