MPY634AM datasheet(6/19 Pages) TI2

6 / 19 page

MPY634

SBFS017A

www.ti.com

RSF = 5.4kΩ

Internal device tolerances make this relationship accurate to

within approximately 25%. Some applications can benefit

from reduction of the SF by this technique. The reduced

input bias current, noise, and drift achieved by this technique

can be likened to operating the input circuitry in a higher

gain, thus reducing output contributions to these effects.

Adjustment of the scale factor does not affect bandwidth.

The MPY634 is fully characterized at VS = ±15V but

operation is possible down to

±8V with an attendant reduc-

tion of input and output range capability. Operation at

voltages greater than

±15V allows greater output swing to be

achieved by using an output feedback attenuator (Figure 1).

As with any wide bandwidth circuit, the power supplies

should be bypassed with high frequency ceramic capacitors.

These capacitors should be located as near as practical to the

power supply connections of the MPY634. Improper by-

passing can lead to instability, overshoot, and ringing in the

output.

FIGURE 2. Basic Multiplier Connection.

10 – SF

MPY634

Out

–V

10k

Ω

–15V

+15V

Y Input

±10V FS

±12V PK

X Input

±10V FS

±12V PK

90k

Ω

OUT, ±12V PK

= (X

1 – X2) (Y1 – Y2)

(Scale = 1V)

Optional

Peaking

Capacitor

F = 200pF

FIGURE 1. Connections for Scale-Factor of Unity.

BASIC MULTIPLIER CONNECTION

Figure 2 shows the basic connection as a multiplier. Accu-

racy is fully specified without any additional user-trimming

circuitry. Some applications can benefit from trimming of

one or more of the inputs. The fully differential inputs

facilitate referencing the input quantities to the source volt-

age common terminal for maximum accuracy. They also

allow use of simple offset voltage trimming circuitry as

shown on the X input.

The differential Z input allows an offset to be summed in

VOUT. In basic multiplier operation, the Z2 input serves as

the output voltage ground reference and should be connected

to the ground of the driven system for maximum accuracy.

A method of changing (lowering) SF by connecting to the

SF pin was discussed previously. Figure 1 shows an alterna-

tive method of changing the effective SF of the overall

circuit by using an attenuator in the feedback connection to

Z1. This method puts the output amplifier in a higher gain

and is thus accompanied by a reduction in bandwidth and an

increase in output offset voltage. The larger output offset

may be reduced by applying a trimming voltage to the high

impedance input, Z2.

The flexibility of the differential Z inputs allows direct

conversion of the output quantity to a current. Figure 3

shows the output voltage differentially-sensed across a se-

ries resistor forcing an output-controlled current. Addition

of a capacitor load then creates a time integration function

useful in a variety of applications such as power computa-

tion.

SQUARER CIRCUIT (FREQUENCY DOUBLER)

Squarer, or frequency doubler, operation is achieved by

paralleling the X and Y inputs of the standard multiplier

circuit. Inverted output can be achieved by reversing the

differential input terminals of either the X or Y input.

Accuracy in the squaring mode is typically a factor of two

better than the specified multiplier mode with maximum

error occurring with small (less than 1V) inputs. Better

accuracy can be achieved for small input voltage levels by

reducing the scale factor, SF.

DIVIDER OPERATION

The MPY634 can be configured as a divider as shown in

Figure 4. High impedance differential inputs for the numera-

tor and denominator are achieved at the Z and X inputs,

Hello

FIGURE 3. Conversion of Output to Current.

MPY634

Out

–V

–15V

+15V

Y Input

±10V FS

±12V PK

X Input

±10V FS

±12V PK

Current

Sensing

Resistor,

S, 2kΩ

min

Integrator

Capacitor

(see text)

OUT =

1 – X2) (Y1 – Y2)

10V

MPY634

Out

–V

–15V

+15V

Y Input

±10V FS

±12V PK

X Input

±10V FS

±12V PK

470k

Ω

Optional

Summing

Input,

Z, ±10V PK

+ Z

1 – X2) (Y1 – Y2)

10V

50k

Ω

+15V

–15V

Ω

Optional Offset

Trim Circuit

OUT, ±12V PK

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