AD734ANZ Datasheet AD734AQ, AD734BQ, AD734SQ/883B | P13-P15

AD734

Rev. E | Page 12 of 20

This error is not 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 can be used. The transistor Qr is provided to cancel

the V

of Qu, and is biased by an external resistor, R2, as shown

in Figure 23. R1 is chosen to set the desired value of U and

consists of a fixed and adjustable resistor.

28kΩ

100kΩ

~60µA

–V

AD734

00827-005

–

Figure 22. Low Accuracy Denominator Control

28kΩ

100kΩ

–V

AD734

00827-006

NOM

Figure 23. Connections for a Fixed Denominator

Table 5 shows useful values of the external components for

setting up nonstandard denominator values.

Table 5. Component Values for Setting Up Nonstandard

Denominator Values

Denominator R1 (Fixed) R1 (Variable) R2

5 V 34.8 kΩ 20 kΩ 120 kΩ

3 V 64.9 kΩ 20 kΩ 220 kΩ

2 V 86.6 kΩ 50 kΩ 300 kΩ

1 V 174 kΩ 100 kΩ 620 kΩ

The denominator can also be current controlled, by grounding

Pin 3 (U0) and withdrawing a current of Iu from Pin 4 (U1).

The nominal scaling relationship is U = 28 × Iu, where u is

expressed in volts and Iu is expressed in milliamps. Note,

however, that while the linearity of this relationship is very

good, it is subject to a scale tolerance of ±20%. Note that the

common-mode range on Pin 3 through Pin 5 actually extends

from 4 V to 36 V below VP; therefore, it is not necessary to

restrict the connection of U0 to ground to use some other

voltage.

The output ER can also be buffered, rescaled, and used as a

general-purpose reference voltage. It is generated with respect

to the negative supply line, Pin 8 (VN), but this is acceptable

when driving one of the signal interfaces. An example is shown

in Figure 31, where a fixed numerator of 10 V is generated for a

divider application. Y2 is tied to VN, but Y1 is 10 V above this;

therefore, the common-mode voltage at this interface is still 5 V

above VN, which satisfies the internal biasing requirements (see

Table 1).

OPERATION AS A MULTIPLIER

All of the connection schemes used in this section are essentially

identical to those used for the AD534, with which the AD734 is

pin compatible. The only precaution to be noted in this regard

is that in the AD534, Pin 3, Pin 5, Pin 9, and Pin 13 are not

internally connected, and Pin 4 has a slightly different purpose.

In many cases, an AD734 can be directly substituted for an

AD534 with immediate benefits in static accuracy, distortion,

feedthrough, and speed. Where Pin 4 was used in an AD534

application to achieve a reduced denominator voltage, this

function can now be much more precisely implemented with

the AD734 using alternative connections (see the Direct

Denominator Control section).

Operation from supplies down to ±8 V is possible. The supply

current is essentially independent of voltage. As is true of all

high speed circuits, careful power supply decoupling is important

in maintaining stability under all conditions of use. The decoupling

capacitors should always be connected to the load ground,

because the load current circulates in these capacitors at high

frequencies. Note the use of the special symbol (a triangle with

the letter L inside it) to denote the load ground (see Figure 24).

Standard Multiplier Connections

Figure 24 shows the basic connections for multiplication. The X

and Y inputs are shown as optionally having their negative nodes

grounded, but they are fully differential, and in many applications

the grounded inputs can be reversed (to facilitate interfacing

with signals of a particular polarity, while achieving some desired

output polarity) or both can be driven.

The AD734 has an input resistance of 50 kΩ ± 20% at the X, Y,

and Z interfaces, which allows ac coupling to be achieved with

moderately good control of the high-pass (HP) corner frequency;

a capacitor of 0.1 μF provides a HP corner frequency of 32 Hz.

When a tighter control of this frequency is needed, or when the

HP corner is above about 100 kHz, an external resistor should

be added across the pair of input nodes.

AD734

X11

X22

VP 14

Y27

ER 9

VN 8

Y16

INPUT

±10V FS

Y INPUT

±10V FS

+15V

–15V

0.1µF

LOAD

GROUND

OPTIONAL

SUMMING INPUT

±10V FS

W =

+ Z

– X

)(Y

–Y

)

10V

00827-007

Figure 24. Basic Multiplier Circuit

AD734

Rev. E | Page 13 of 20

At least one of the two inputs of any pair must be provided with

a dc path (usually to ground). The careful selection of ground

returns is important in realizing the full accuracy of the AD734.

The Z2 pin is normally connected to the load ground, which can be

remote in some cases. It can also be used as an optional summing

input (see Equation 3 and Equation 4) having a nominal FS

input of ±10 V and the full 10 MHz bandwidth.

In applications where high absolute accuracy is essential, the

scaling error caused by the finite resistance of the signal source(s)

may be troublesome; for example, a 50 Ω source resistance at

just one input introduces a gain error of −0.1%; if both the X

and Y inputs are driven from 50 Ω sources, the scaling error in

the product is −0.2%. If the source resistances are known, this

gain error can be completely compensated by including the

appropriate resistance (50 Ω or 100 Ω, respectively, in the

preceding cases) between the output, W (Pin 12), and the Z1

feedback input (Pin 11). If Rx is the total source resistance

associated with the X1 and X2 inputs, and Ry is the total source

resistance associated with the Y1 and Y2 inputs, and neither Rx

nor Ry exceeds 1 kΩ, a resistance of Rx + Ry in series with

Pin Z1 provides the required gain restoration.

Pin 9 (ER) and Pin 13 (DD) should be left unconnected in this

application. The U inputs (Pin 3, Pin 4, and Pin 5) are shown

connected to ground; they can alternatively be connected to

VN, if desired. In applications where Pin 2 (X2) happens to

be driven with a high amplitude, high frequency signal, the

capacitive coupling to the denominator control circuitry via

an ungrounded Pin 3 can cause high frequency distortion.

However, the AD734 can be operated without modification in

AD534 socket and these three pins left unconnected with the

preceding caution noted.

AD734

X INPUT

±10V FS

Y INPUT

±10V FS

+15

–15V

0.1µF

LOAD

±10mA MAX FS

±10V MAXIMUM

LOAD VOLTAGE

– X

)(Y

–Y

)

10V

50kΩ

0827-008

Figure 25. Conversion of Output to a Current

Current Output

It may occasionally be desirable to convert the output voltage to

a current. In correlation applications, for example, multiplication is

followed by integration; if the output is in the form of a current,

a simple grounded capacitor can perform this function. Figure 25

shows how this can be achieved. The op amp forces the voltage

across Z1 and Z2, and thus across the resistor, RS, to be the

product XY/U. Note that the input resistance of the Z interface

is in shunt with RS, which must be calculated accordingly.

The smallest FS current is simply ±10 V/50 kΩ, or ±200 μA,

with a tolerance of about 20%. To guarantee a 1% conversion

tolerance without adjustment, R

must be less than 2.5 kΩ. The

maximum full-scale output current should be limited to about

±10 mA (thus, R

= 1 kΩ). This concept can be applied to all

connection modes, with the appropriate choice of terminals.

Squaring and Frequency-Doubling

Squaring of an input signal, E, is achieved by connecting the X

and Y inputs in parallel; the phasing can be chosen to produce

an output of E

/U or −E

/U as desired. The input can have

either polarity, but the basic output is either always positive or

negative; as for multiplication, the Z2 input can be used to add a

further signal to the output.

When the input is a sine wave, a squarer behaves as a frequency

doubler, because

(Esinwt)

= E

(1 − cos2wt)/2 (8)

Equation 8 shows a dc term at the output, which varies strongly

with the amplitude of the input, E. This dc term can be avoided

using the connection shown in Figure 26, where an RC network

is used to generate two signals whose product has no dc term.

The output is

⎟

⎠

⎞

⎜

⎝

⎛

⎭

⎬

⎫

⎩

⎨

⎧

⎟

⎠

⎞

⎜

⎝

⎛

−

⎭

⎬

⎫

⎩

⎨

⎧

⎟

⎠

⎞

⎜

⎝

⎛

V10

sin

ππ

(9)

for w = 1/CR1, which is just

W = E

(cos2wt)/(10 V) (10)

which has no dc component. To restore the output to ±10 V

when E = 10 V, a feedback attenuator with an approximate ratio

of 4 is used between W and Z1; this technique can be used

wherever it is desired to achieve a higher overall gain in the

transfer function.

The values of R3 and R4 include additional compensation for the

effects of the 50 kΩ input resistance of all three interfaces; R2 is

included for a similar reason. These resistor values should not

be altered without careful calculation of the consequences. With

the values shown, the center frequency f

is 100 kHz for C =

1 nF. The amplitude of the output is only a weak function of

frequency; the output amplitude is 0.5% too low at f = 0.9f

and

f = 1.1f

. The cross-connection is simply to produce the cosine

output with the sign shown in Equation 10; however, the sign in

this case is rarely important.

AD734

Rev. E | Page 14 of 20

AD734

+15

4.32kΩ

13kΩ

1.6kΩ

–15V

0.1µF

0827-009

Esinωt E

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

X INPUT

+0.1V TO

+10V

OPTIONAL

SUMMING

INPUT

±10V FS

+15

Z INPUT

±10V FS

–15V

0.1µF

W = 10 +Y1

– Z

)

– X

)

00827-010

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

OPTIONAL

SUMMING

INPUT

±10V FS

+15

Z INPUT

+10mV TO

+10V

–15V

0.1µF

00827-011

–

W = (10V) (Z

– Z

) + 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

2121

)(

))((

YYXX

W +

−

= (11)

where the

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

but the difference U = U

− U

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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