REV. E

AD630

–8–

the system input tied to 0 V, and a switching or carrier wave-

form applied to the comparator, a low level square wave will

appear at the output. The differential offset adjustment potenti-

ometers can be used to null the amplitude of this square wave

(Pins 3 and 4). The common-mode offset adjustment can be

used to zero the residual dc output voltage (Pins 5 and 6).

These functions should be implemented using 10k trim poten-

tiometers with wipers connected directly to Pin 8 as shown in

Figures 9a and 9b.

CHANNEL STATUS OUTPUT

The channel status output, Pin 7, is an open collector output

input channels is active. The output will be active (pulled low)

when Channel A is selected. This output can also be used to

supply positive feedback around the comparator. This produces

hysteresis which serves to increase noise immunity. Figure 7

shows an example of how hysteresis may be implemented. Note

that the feedback signal is applied to the inverting (–) terminal

of the comparator to achieve positive feedback. This is because

the open collector channel status output inverts the output sense

of the internal comparator.

1M

100k

100k

–15V

+5V

100

7

8

9

10

Figure 7. Comparator Hysteresis

The channel status output may be interfaced with TTL inputs

as shown in Figure 8. This circuit provides appropriate level

shifting from the open-collector AD630 channel status output to

TTL inputs.

–15V

+5V

TTL INPUT

AD630

+15V

IN 914s

6.8k

22k

100k

2N2222

7

8

Figure 8. Channel Status—TTL Interface

APPLICATIONS: BALANCED MODULATOR

Perhaps the most commonly used configuration of the AD630 is

the balanced modulator. The application resistors provide precise

symmetric gains of

±1 and ±2. The ±1 arrangement is shown in

Figure 9a and the

±2 arrangement is shown in Figure 9b. These

cases differ only in the connection of the 10 k

Ω feedback resistor

(Pin 14) and the compensation capacitor (Pin 12). Note the use

of the 2.5 k

Ω bias current compensation resistors in these

examples. These resistors perform the identical function in the

±1 gain case. Figure 10 demonstrates the performance of the

AD630 when used to modulate a 100 kHz square wave carrier

with a 10 kHz sinusoid. The result is the double sideband sup-

pressed carrier waveform.

These balanced modulator topologies accept two inputs, a signal

(or modulation) input applied to the amplifying channels and a

reference (or carrier) input applied to the comparator.

MODULATED

OUTPUT

SIGNAL

CARRIER

INPUT

CM

ADJ

DIFF

ADJ

2.5k

AMP A

AMP B

–V

10k

10k

5k

9

10

COMP

1

15

7

16

14

13

12

2

20

AD630

A

B

2.5k

19

18

17

11

8

6

5

10k

4

3

10k

MODULATION

INPUT

Figure 9a. AD630 Configured as a Gain-of-One Balanced

Modulator

MODULATED

OUTPUT

SIGNAL

CARRIER

INPUT

CM

ADJ

DIFF

ADJ

2.5k

AMP A

AMP B

–V

10k

10k

5k

9

10

COMP

1

15

7

16

14

13

12

2

20

AD630

A

B

2.5k

19

18

17

11

8

6

5

10k

4

3

10k

MODULATION

INPUT

Figure 9b. AD630 Configured as a Gain-of-Two Balanced

Modulator

10V

5V

5V

20 s

MODULATION

INPUT

CARRIER

INPUT

OUTPUT

SIGNAL

Figure 10. Gain-of-Two Balanced Modulator Sample

Waveforms