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AD734

Rev. E | Page 14 of 20

AD734

VP 14

W 12

Z1 11

Z2 10

ER 9

VN 8

+15V

4.32kΩ

13kΩ

1.6kΩ

–15V

0.1µF

Esinωt

E2 cos2ωt/10V

Figure 26. Frequency Doubler

OPERATION AS A DIVIDER

The AD734 supports two methods for performing analog

division. The first is based on the use of a multiplier in a

feedback loop. This is the standard mode recommended for

multipliers having a fixed scaling voltage, such as the AD534,

and is described in this section. The second uses the AD734’s

unique capability for externally varying the scaling (denominator)

voltage directly, and is described in the Division by Direct

Denominator Control section.

Feedback Divider Connections

Figure 27 shows the connections for the standard (AD534)

divider mode. Feedback from the output, W, is now taken to the

Y2 (inverting) input, which, if the X input is positive, establishes a

negative feedback path. Y1 should normally be connected to the

ground associated with the load circuit, but can optionally be

used to sum a further signal to the output. If desired, the

polarity of the Y input connections can be reversed, with W

connected to Y1 and Y2 used as the optional summation input. In

this case, either the polarity of the X input connections must be

reversed or the X input voltage must be negative.

AD734

VP 14

W 12

Z1 11

Z2 10

ER 9

VN 8

X INPUT

+0.1V TO

+10V

OPTIONAL

SUMMING

INPUT

±10V FS

+15V

Z INPUT

±10V FS

–15V

0.1µF

W = 10

+Y1

(Z2 – Z1)

(X1 – X2)

Figure 27. Standard (AD534) Divider Connection

The numerator input, which is differential and can have either

polarity, is applied to Pin Z1 and Pin Z2. As with all dividers

based on feedback, the bandwidth is directly proportional to

the denominator, being 10 MHz for X = 10 V and reducing to

100 kHz for X = 100 mV. This reduction in bandwidth, and

the increase in output noise (which is inversely proportional

to the denominator voltage) preclude operation much below a

denominator of 100 mV. Division using direct control of the

denominator (see Figure 29) does not have these shortcomings.

AD734

VP 14

W 12

Z1 11

Z2 10

ER 9

VN 8

OPTIONAL

SUMMING

INPUT

±10V FS

+15V

Z INPUT

+10mV TO

+10V

–15V

0.1µF

–

W = (10V) (Z2 – Z1) + S

Figure 28. Connection for Square Rooting

Connections for Square-Rooting

The AD734 can be used to generate an output proportional to

the square root of an input using the connections shown in

Figure 28. Feedback is now via both the X and Y inputs, and is

always negative because of the reversed polarity between these

two inputs. The Z input must have the polarity shown, but

because it is applied to a differential port, either polarity of

input can be accepted with reversal of Z1 and Z2, if necessary.

The diode, D, which can be any small-signal type (1N4148

being suitable), is included to prevent a latching condition,

which can occur if the input is momentarily of the incorrect

polarity of the input. The output is always negative.

Note that the loading on the output side of the diode is provided

by the 25 kΩ of input resistance at X1 and Y2, and by the user’s

load. In high speed applications, it may be beneficial to include

further loading at the output (to 1 kΩ minimum) to speed up

response time. As in previous applications, a further signal, shown

in Figure 28 as S, can be summed to the output; if this option is

not used, this node should be connected to the load ground.

DIVISION BY DIRECT DENOMINATOR CONTROL

The AD734 can be used as an analog divider by directly varying

the denominator voltage. In addition to providing much higher

accuracy and bandwidth, this mode also provides greater

flexibility, because all inputs remain available. Figure 29 shows

the connections for the general case of a three-input multiplier

divider, providing the function

)

(

)

)(

(

−

(11)

where the

X, Y, and Z signals can all be positive or negative,

but the difference U = U1 − U2 must be positive and in the range

10 mV to 10 V. If a negative denominator voltage must be used,

simply ground the noninverting input of the op amp. As previ-

ously noted, the X input must have a magnitude of less than 1.25U.

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