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| 型号： | AB-175 |
| 英文描述： | AB-175 - CODING SCHEMES USED WITH DATA CONVERTERS |
| 中文描述： | 抗体- 175 -编码方案使用数据转换器 |
| 文件页数： | 2/5页 |
| 文件大小： | 37K |
| 代理商： | AB-175 |
2
III). The digital count continues to increase proportionally to
the analog input until the positive full scale is reached at a
full digital count (1111) as shown by Table III.
With BOB coding, the MSB can be considered a sign
indicator whereas a logic “0” indicates a negative analog
value, and a logic “1” indicates an analog value greater than
or equal to BPZ.
(1)
MNEMONIC
DIGITAL CODE
V
t–
V
CODE
V
t+
–FS
0000
0001
0010
0011
–5.000
–4.375
–3.750
–3.125
–4.6875
–4.0625
–3.4375
–2.8125
–4.6875
–4.0625
–3.4375
1/2 –FS
0100
0101
0110
–2.8125
–2.1875
–1.5625
–2.500
–1.875
–1.250
–2.1875
–1.5625
–0.9375
BPZ – 1V
LSB
BPZ
0111
–0.9375
–0.625
–0.3125
1000
–0.3125
0.000
+0.3125
BPZ + 1V
LSB
1001
1010
1011
+0.3125
+0.9375
+1.5625
+0.625
+1.250
+1.875
+0.9375
+1.5625
+2.1875
1/2 +FS
1100
1101
1110
+2.1875
+2.8125
+3.4375
+2.500
+3.125
+3.750
+2.8125
+3.4375
+4.0625
+FS
1111
+4.0625
+4.375
TABLE III. BOB Coding Scheme.
The ADS7800, a 12-bit, 333kHz, sampling analog-to-digital
converter, utilizes the Bipolar Offset Binary output code to
implement its
±
5 and
±
10V input ranges. The DAC780x
series of digital-to-analog converters also use this scheme in
each of their three different interface formats (serial, 8-bits
+ 4-bits parallel, and 12-bit parallel).
COB — COMPLEMENTARY OFFSET BINARY
Complementary Offset Binary coding, like its counterpart
BOB, is also for use in systems where the analog signal is
bipolar. The relationship between COB and BOB is that
each coding scheme is the one’s complement (all bits in-
verted) of the other.
COB coding begins with digital zero (0000) at the positive
full scale. By incrementing the digital count, the corre-
sponding analog value will approach the negative full scale
in –1V
LSB
steps, passing through bipolar zero on the way.
This “zero crossing” occurs at a digital code of 0111 (see
Table IV). As the digital count continues to increase, the
analog signal goes more negative until the negative full
scale is reached at a full digital count (1111) as shown by
Table IV.
With COB coding, like BOB coding, the MSB can also be
considered a sign indicator whereas a logic “1” indicates a
negative analog value, and a logic “0” indicates an analog
value greater than or equal to BPZ.
(2)
MNEMONIC
DIGITAL CODE
V
t–
V
CODE
V
t+
–FS
1111
1110
1101
1100
–5.000
–4.375
–3.750
–3.125
–4.6875
–4.0625
–3.4375
–2.8125
–4.6875
–4.0625
–3.4375
1/2 –FS
1011
1010
1001
–2.8125
–2.1875
–1.5625
–2.500
–1.875
–1.250
–2.1875
–1.5625
–0.9375
BPZ – 1V
LSB
1000
–0.9375
–0.625
–0.3125
BPZ
0111
–0.3125
0.000
+0.3125
BPZ + 1V
LSB
0110
0101
0100
+0.3125
+0.9375
+1.5625
+0.625
+1.250
+1.875
+0.9375
+1.5625
+2.1875
1/2 +FS
0011
0010
0001
+2.1875
+2.8125
+3.4375
+2.500
+3.125
+3.750
+2.8125
+3.4375
+4.0625
+FS
0000
+4.0625
+4.375
TABLE IV. COB Coding Scheme.
NOTE: (1) The V
t+
transition to BPZ from a negative value (0111 to 1000) actually occurs at –0.3125V causing the MSB to go “positive” at a negative value. (2) The V
t+
transition
to BPZ from a negative value (1000 to 0111) actually occurs at –0.3125V causing the MSB to go “positive” at a negative value. (3) The V
t+
transition to BPZ from a negative
value (1111 to 0000) actually occurs at –0.3125V causing the MSB to go “positive” at a negative value.
BTC — BINARY TWO’S COMPLEMENT
Binary Two’s Complement coding is the type of coding used
by most microprocessor or math processor based systems for
mathematical algorithms, and is also the coding scheme
which the digital audio industry has decided to use as its
standard.
Binary Two’s Complement coding is also a scheme de-
signed for bipolar analog signals. It is very similar to BOB,
but does not appear so. The only difference between BOB
and BTC is that the MSB has been inverted.
Unfortunately, BTC is not as straightforward as the schemes
previously mentioned. The codes are not continuous from
one end of the analog “spectrum” to the other due to a
discontinuity which occurs at BPZ.
Digital zero (0000) corresponds to BPZ, and the digital
count increments to its maximum positive code of 0111 as
the analog voltage approaches and reaches its positive full
scale value. The code then resumes at the negative full scale
value at a digital code of 1000, and then approaches BPZ
until a digital value of 1111 is reached at one LSB value
below BPZ.
With the BTC coding scheme, the MSB can also be consid-
ered a sign indicator. When the MSB is a logic “0” a positive
value is indicated, and when the MSB is a logic “1” a
negative value is indicated.
(3)
This is the coding scheme which is used with Burr-Brown’s
DSP interface chips (DSP101/DSP102 analog input and
DSP201/DSP202 analog output) designed for “zero chip
interface” to most of the popular digital signal processors
available today. Binary Two’s Complement is also one of
the codes utilized by the ADC603 and ADC614 high speed
analog-to-digital converters, and, of course, all of Burr-
Brown’s PCM digital audio converters.
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