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AD834S

500 MHz Four-Quadrant Multiplier

Analog Devices 

AD834

+5V

X-INPUT

؎1V FS

49.9⍀

1␮F

OPTIONAL

CERAMIC

TERMINATION

RESISTOR

8765

X2 X1 +VS W1

AD834

Y1 Y2 –VS W2

1234

LOAD

Y-INPUT

؎1V FS

OPTIONAL

TERMINATION

RESISTOR

1␮F

CERAMIC

4.7⍀

–5V

Figure 6. Transformer-Coupled Output

A particularly effective type of transformer is the balun*, which

is a short length of transmission line wound on to a toroidal

ferrite core. Figure 7 shows this arrangement used to convert

the bal(anced) output to an un(balanced) one (hence the use of

the term). Although the symbol used is identical to that for a

transformer, the mode of operation is quite different. In the first

place, the load should now be equal to the characteristic imped-

ance of the line (although this will usually not be critical for

short line lengths). The collector load resistors RC may also be

chosen to reverse terminate the line, but again this will only be

necessary when an electrically long line is used. In most cases,

RC will be made as large as the dc conditions allow to minimize

power loss to the load. The line may be a miniature coaxial

cable or a twisted pair.

X-INPUT

؎1V FS

Y-INPUT

؎1V FS

1.5RC

1␮F

OPTIONAL

CERAMIC RC RC

TERMINATION

RESISTOR

C

8765

X2 X1 +VS W1

AD834

Y1 Y2 –VS W2

1234

C

+5V

OUTPUT

BALUN

RL

SEE

TEXT

OPTIONAL

TERMINATION

RESISTOR

1␮F

CERAMIC

4.7⍀

–5V

Figure 7. Using a Balun at the Output

It is important to note that the upper bandwidth limit of the

balun is determined only by the quality of the transmission line;

hence, it will usually exceed that of the multiplier. This is unlike

a conventional transformer where the signal is conveyed as a

flux in a magnetic core and is limited by core losses and leakage

inductance. The lower limit on bandwidth is determined by the

series inductance of the line, taken as a whole, and the load

resistance (if the blocking capacitors C are sufficiently large).

In practice, a balun can provide excellent differential-to-single-sided

conversion over much wider bandwidths than a transformer.

WIDEBAND MULTIPLIER CONNECTIONS

Where operation down to dc and a ground-based output are

necessary, the configuration shown in Figure 8 can be used.

The element values were chosen in this example to result in a

full-scale output of ± 1 V at the load, so the overall multiplier

transfer function is

W = (X1 – X2)(Y1 – Y2)

where it is understood that the inputs and output are in volts. The

polarity of the output can be reversed simply by reversing either

the X or Y input.

X

؎1V

Y

؎1V

49.9⍀

167⍀

0.1␮F

8765

X2 X1 +VS W1

AD834

Y1 Y2 –VS W2

1234

49.9⍀

49.9⍀

49.9⍀

0.01␮F

0.1␮F 0.01␮F

3.01k⍀

+5V

261⍀

261⍀

49.9⍀

3.01k⍀

1␮F

2.7⍀

LOAD

49.9⍀

4.7⍀

3.74k⍀

3.74k⍀

–

AD5539

+

1␮F

90.9⍀

2.7⍀

–5V

Figure 8. Sideband DC-Coupled Multiplier

The op amp should be chosen to support the desired output

bandwidth. The AD5539 is shown here, providing an overall

system bandwidth of 100 MHz. Many other choices are possible

where lower post multiplication bandwidths are acceptable. The

level shifting network places the input nodes of the op amp to

within a few hundred millivolts of ground using the recommended

balanced supplies. The output offset may be nulled by including

a 100 W trim pot between each of the lower pair of resistors

(3.74 kW) and the negative supply.

The pulse response for this circuit is shown in Figure 9; the X

input was a pulse of 0 V to 1 V and the Y input was 1 V dc. The

transition times at the output are about 4 ns.

200mV

100

90

10ns

10

0%

*For a good treatment of baluns, see “Transmission Line Transformers” by Jerry

Sevick; American Radio Relay League publication.

REV. D

–7–

Figure 9. Pulse Response for the Circuit of Figure 8

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