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| 型号： | AB-178 |
| 英文描述： | AB-178 - CDAC ARCHITECTURE PLUS RESISTOR DIVIDER GIVES ADC574 PINOUT WITH SAMPLING. LOW POWER. NEW INPUT RANGES |
| 中文描述： | 抗体- 178 -华助建筑集锦电阻分压器使ADC574引脚排列，取样。低功耗。新的输入范围 |
| 文件页数： | 1/5页 |
| 文件大小： | 37K |
| 代理商： | AB-178 |
Mailing Address: PO Box 11400 Tucson, AZ 85734 Street Address: 6730 S. Tucson Blvd. Tucson, AZ 85706
Tel: (602) 746-1111 Twx: 910-952-111 Telex: 066-6491 FAX (602) 889-1510 Immediate Product Info: (800) 548-6132
CODING SCHEMES USED WITH
DATA CONVERTERS
Jason Albanus
TABLE I. USB Coding Scheme.
MNEMONIC
DIGITAL CODE
V
t–
V
CODE
V
t+
Zero
0000
0.000
0.3125
+1 V
LSB
0001
0010
0011
0.3125
0.9375
1.5625
0.625
1.250
1.875
0.9375
1.5625
2.1875
1/4 FSR
0100
0101
0110
0111
2.1875
2.8125
3.4375
4.0625
2.500
3.125
3.750
4.375
2.8125
3.4375
4.0625
4.6875
1/2 FSR
1000
1001
1010
1011
4.6875
5.3125
5.9375
6.5625
5.000
5.625
6.250
6.875
5.3125
5.9375
6.5625
7.1875
3/4 FSR
1100
1101
1110
7.1875
7.8125
8.4375
7.500
8.125
8.750
7.8125
8.4375
9.0625
+FS
1111
9.0625
9.375
MNEMONIC
DIGITAL CODE
V
t–
V
CODE
V
t+
Zero
1111
0.000
0.3125
+1V
LSB
1110
1101
1100
0.3125
0.9375
1.5625
0.625
1.250
1.875
0.9375
1.5625
2.1875
1/4 FSR
1011
1010
1001
1000
2.1875
2.8125
3.4375
4.0625
2.500
3.125
3.750
4.375
2.8125
3.4375
4.0625
4.6875
1/2 FSR
0111
0110
0101
0100
4.6875
5.3125
5.9375
6.5625
5.000
5.625
6.250
6.875
5.3125
5.9375
6.5625
7.1875
3/4 FSR
0011
0010
0001
7.1875
7.8125
8.4375
7.500
8.125
8.750
7.8125
8.4375
9.0625
+FS
0000
9.0625
9.375
TABLE II. CSB Coding Scheme.
BOB — BIPOLAR OFFSET BINARY
Bipolar Offset Binary coding, as the name implies, is for use
in bipolar systems (where the analog voltage can be positive
and negative). This coding scheme is very similar to USB
coding since, as the analog voltage increases, the digital
count also increases.
BOB coding begins with digital zero (0000) at the negative
full scale. By incrementing the digital count, the correspond-
ing analog value will approach the positive full scale in
1V
LSB
steps, passing through bipolar zero on the way. This
“zero crossing” occurs at a digital code of 1000 (see Table
With the recent proliferation of analog-to-digital converters
(ADCs) and digital-to-analog converters (DACs), and the
variety of digital coding schemes which they use, has come
a need to understand these different coding schemes which
converters use to talk to the “digital world”. The purpose of
this article is to describe the individual coding schemes used
with ADCs and DACs manufactured by Burr-Brown, and
explain their relationships.
Following this text is a list of abbreviations and definitions
intended to clarify any questions regarding the nomenclature
which has been used.
Throughout this guide, examples and tables given are for a
4-bit data converter. In unipolar and bipolar examples alike,
the Full Scale Range (FSR) is 10V creating a V
LSB
of
0.625V. For unipolar examples, minus full scale (–FS ) is 0V
and plus full scale (+FS) is 10V; for bipolar examples, –FS
is –5V and +FS is +5V.
USB — UNIPOLAR STRAIGHT BINARY
The Unipolar Straight Binary coding is perhaps the simplest
coding scheme to understand. As the name implies, it is a
coding scheme which is used only for unipolar voltages.
When using USB coding, the digital count begins at all zeros
(0000) at a V
CODE
of 0V (V
t+
= 0V + 1/2V
LSB
and there is
no V
t–
). As the digital code increments, the analog voltage
increases one V
LSB
at a time, and the digital count ends
(1111) at the positive full scale value. Table I shows how the
USB codes correspond to analog voltages for a 4-bit digital
system.
Unipolar Straight Binary is the coding scheme used by the
ADC7802 and ADS7803.
CSB — COMPLEMENTARY STRAIGHT BINARY
The Complementary Straight Binary coding scheme is the
exact digital opposite (one’s complement) of Unipolar
Straight Binary. CSB coding, like its counterpart USB, is
also restricted to unipolar systems.
When using CSB coding with a digital system, the digital
count begins at all zeros (0000) at the positive full scale
value. As the digital code increments, the analog voltage
decreases one V
LSB
at at time, until 0V is reached at a digital
code of 1111. The relationship between CSB coding and its
corresponding analog voltages can be seen in Table II.
1991 Burr-Brown Corporation
AN-175
Printed in U.S.A. March, 1991
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