参数资料
型号: AB-179
英文描述: AB-179 - VIDEO OPERATIONAL AMPLIFIER
中文描述: 抗体- 179 -视频运算放大器
文件页数: 3/5页
文件大小: 37K
代理商: AB-179
3
MNEMONIC
DIGITAL CODE
V
t–
V
CODE
V
t+
–FS
1000
1001
1010
1011
–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
1100
1101
1110
–2.8125
–2.1875
–1.5625
–2.500
–1.875
–1.250
–2.1875
–1.5625
–0.9375
BPZ – 1V
LSB
1111
–0.9375
–0.625
–0.3125
BPZ
0000
–0.3125
0.000
+0.3125
BPZ + 1V
LSB
0001
0010
0011
+0.3125
+0.9375
+1.5625
+0.625
+1.250
+1.875
+0.9375
+1.5625
+2.1875
1/2 +FS
0100
0101
0110
+2.1875
+2.8125
+3.4375
+2.500
+3.125
+3.750
+2.8125
+3.4375
+4.0625
+FS
0111
+4.0625
+4.375
TABLE V. BTC Coding Scheme.
MNEMONIC
DIGITAL CODE
V
t-
V
CODE
V
t+
–FS
0111
0110
0101
0100
–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
0011
0010
0001
–2.8125
–2.1875
–1.5625
–2.500
–1.875
–1.250
–2.1875
–1.5625
–0.9375
BPZ – 1V
LSB
0000
–0.9375
–0.625
–0.3125
BPZ
1111
–0.3125
0.000
+0.3125
BPZ + 1V
LSB
1110
1101
1100
+0.3125
+0.9375
+1.5625
+0.625
+1.250
+1.875
+0.9375
+1.5625
+2.1875
1/2 +FS
1011
1010
1001
+2.1875
+2.8125
+3.4375
+2.500
+3.125
+3.750
+2.8125
+3.4375
+4.0625
+FS
1000
+4.0625
+4.375
TABLE VI. CTC Coding Scheme.
CTC — COMPLEMENTARY TWO’S COMPLEMENT
Complementary Two’s Complement coding is also a scheme
designed for bipolar analog signals. It is the one’s comple-
ment of its counterpart BTC, and is also very similar to
COB, although this relationship is not immediately obvious.
The only difference between COB and CTC is that the MSB
has been inverted.
With CTC coding, digital “zero” is at an analog voltage
which is slightly less (1 LSB) than analog bipolar zero. As
the digital count increments, the analog voltage becomes
more negative until all of the bits are high except for the
MSB (0111). At this point, the digital code corresponds to
the analog negative full scale. The next step in incrementing
the digital code would be to have the MSB a logic “1”, and
the rest of the bits as logic “0”s (1000), and this code
represents the analog positive full scale value. As the digital
codes continue to increment, the corresponding analog volt-
age decreases until BPZ is obtained. Table VI demonstrates
this analog/digital relationship.
With Complementary Two’s Complement coding, the MSB
is also a sign indicator with its states of “0” and “1”
representing negative and positive voltages, respectively.
This code is also used by Burr-Brown’s high speed ADC603
and ADC614. These converters accomplish this dual code
task by providing an input for code selection.
MANIPULATING BETWEEN VARIOUS CODES
The input and output codings used with ADCs and DACs is
varied, and an individual converter may be capable of
utilizing one or more coding scheme. However, with all of
these schemes available, the desired scheme is not always
readily available with the particular converter of interest. Do
not fear, because converting one coding scheme to another,
to match a particular system, is very easy as long as you wish
to convert a bipolar scheme to another bipolar scheme; or a
unipolar scheme into another unipolar scheme. The only
devices required for any transformation are digital logic
“inverters”, however, some of the transformations can be
achieved by using analog components.
(4)
The following
section will be divided into sections depending on how the
transformation is to be accomplished.
Inversion of all Bits
USB to CSB and CSB to USB
BOB to COB and COB to BOB
BTC to CTC and CTC to BTC
The CSB scheme is simply the USB code with all of the bits
inverted (one’s complement). This is also how to perform
most of the transformation of BOB to COB, and BTC to
CTC. For conversion of unipolar schemes, there is only a
digital “solution”, and conversion of bipolar schemes may
be done with analog or digital components.
Converting between the bipolar codes in an analog fash-
ion, all that’s needed is one op amp configured for a gain
of –1V/V (see Figure 2). This op amp can be used on the
input stage of an ADC or the output stage of a DAC.
Some sample and hold amplifiers, such as the SHC5320,
are configurable for a gain of –1V/V, providing very easy
conversion between these codes in an analog-to-digital
system. Remember that either +1V
LSB
or –1V
LSB
must be
summed in with the analog value.
The bipolar transformations may be quite straightforward
when done in the analog domain; however, to convert
digitally, an individual logic “inverter” must be used on
every data line, input or output (see Figure 1), as with the
unipolar schemes.
The ADC603 and ADC614 allow both BTC and CTC
coding schemes by providing an “Output Logic Invert” input
pin. This flexibility allows these converters to be used in
even more applications easier than if just one scheme had
been implemented.
NOTE: (4) When converting bipolar digital schemes, regardless of whether the transformation is done digitally or in an analog fashion, a value of either +1V
LSB
or –1V
LSB
must
be summed in with the analog value. This is due to the assymetric nature of the codes around bipolar zero (see definition of V
t
). This addition of one V
LSB
is relatively simple,
since most data converters allow for an offset adjustment which can accomodate this.
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