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參數(shù)資料
| 型號(hào)： | AD734 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | 10 MHz, 4-Quadrant Multiplier/Divider(10MHz,四象限乘法器/除法器) |
| 中文描述： | 10兆赫，四象限乘法器/除法器（10MHz的，四象限乘法器/除法器） |
| 文件頁(yè)數(shù)： | 5/12頁(yè) |
| 文件大小： | 283K |
| 代理商： | AD734 |
AD734
REV. B
–5–
After temperature-correction (block T C), the reference voltage
is applied to transistor Qd and trimmed resistor Rd, which
generate the required reference current. T ransistor Qu and
resistor Ru are not involved in setting up the internal denominator,
and their associated control pins U0, U1 and U2 will normally
be grounded. T he reference voltage is also made available, via
the 100 k
resistor Rr, at Pin 9 (ER); the purpose of Qr is
explained below.
When the control pin DD (denominator disable) is connected to
VP, the internal source of Iu is shut off, and the collector cur-
rent of Qu must provide the denominator current. T he resistor
Ru is laser-trimmed such that the multiplier denominator is
exactly equal to the voltage across it (that is, across pins U1 and
U2). Note that this trimming only sets up the correct internal
ratio; the absolute value of Ru (nominally 28 k
) has a
tolerance of
±
20%. Also, the alpha of Qu, (typically 0.995)
which might be seen as a source of scaling error, is canceled by
the alpha of other transistors in the complete circuit.
In the simplest scheme (Figure 3), an externally-provided
control voltage, V
G
, is applied directly to U0 and U2 and the
resulting voltage across Ru is therefore reduced by one V
BE
. For
example, when V
G
= 2 V, the actual value of U will be about
1.3 V. T his error will not be important in some closed-loop
applications, such as automatic gain control (AGC), but clearly
is not acceptable where the denominator value must be well-
defined. When it is required to set up an accurate, fixed value of
U, the on-chip reference may be used. T he transistor Qr is
provided to cancel the V
BE
of Qu, and is biased by an external
resistor, R2, as shown in Figure 4. R1 is chosen to set the de-
sired value of U and consists of a fixed and adjustable resistor.
Ru
28k
Qu
Iu
U0
U1
U2
VP
DD
AD734
~
60μA
+V
S
–V
S
NC
NC
ER
VN
Qr
Rr
100k
V
G
3
4
5
9
8
13
14
Figure 3. Low-Accuracy Denominator Control
Qu
Iu
U0
U1
U2
VP
DD
AD734
+V
S
–V
S
NC
NOM
8V
Qr
ER
VN
R2
Ru
28k
Rr
100k
4
5
8
9
14
13
R1
3
Figure 4. Connections for a Fixed Denominator
T able I shows useful values of the external components for set-
ting up nonstandard denominator values.
the AD734 can be operated using the standard (AD534) divider
connections (Figure 8), when the negative feedback path is
established via the Y
2
input. Substituting W for Y
2
in Equation
(2), we get
(
X
1
X
2
(
In this case, note that the variable X is now the denominator,
and the above restriction (X /U
≤
1.25) on the magnitude of the
X input does not apply. However, X must be positive in order
for the feedback polarity to be correct. Y
1
can be used for
summing purposes or connected to the load ground if not
needed. T he shorthand form in this case is
(
+
X
(
In some cases, feedback may be connected to two of the avail-
able inputs. T his is true for the square-rooting connections (Fig-
ure 9), where W is connected to both X
1
and Y
2
. Setting X
1
=
W and Y
2
= W in Equation (2), and anticipating the possibility
of again providing a summing input, so setting X
2
= S and Y
1
=
S, we find, in shorthand form
W
=
U
Z
2
Z
1
)
)
+
Y
1
.
(5)
±
W
(
)
= +
U
)
±
Z
)
)
+ ±
Y
)
.
(6)
±
W
(
)
=
+
U
(
)
+
Z
(
)
+ ±
S
)
.
(7)
T his is seen more generally to be the geometric-mean function,
since both U and Z can be variable; operation is restricted to
one quadrant. Feedback may also be taken to the U-interface.
Full details of the operation in these modes is provided in the
appropriate section of this data sheet.
Direct Denominator Control
A valuable new feature of the AD734 is the provision to replace
the internal denominator voltage, U, with any value from
+10 mV to +10 V. T his can be used (1) to simply alter the
multiplier scaling, thus improve accuracy and achieve reduced
noise levels when operating with small input signals; (2) to
implement an accurate two-quadrant divider, with a 1000:1 gain
range and an asymptotic gain-bandwidth product of 200 MHz;
(3) to achieve certain other special functions, such as AGC or
rms.
Figure 2 shows the internal circuitry associated with denomina-
tor control. Note first that the denominator is actually propor-
tional to a current, Iu, having a nominal value of 356
μ
A for
U = 10 V, whereas the primary reference is a voltage, generated
by a buried-Zener circuit and laser-trimmed to have a very low
temperature coefficient. T his voltage is nominally 8 V with a
tolerance of
±
10%.
Ru
28k
Rd
NOM
22.5k
Qu
Qd
NOM
8V
Rr
100k
TC
Qr
NEGATIVE SUPPLY
NOMINALLY
356μA for
U = 10V
Iu
U0
U1
U2
VP
DD
ER
VN
AD734
LINK TO
DISABLE
8
9
14
13
3
4
5
Figure 2. Denominator Control Circuitry
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