AD630ADZ datasheet(16/20 Pages) AD

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AD630

Data Sheet

Rev. G | Page 16 of 20

APPLICATIONS INFORMATION

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 28 and the ±2 arrangement is shown in

Figure 29. These cases differ only in the connection of the

10 kΩ feedback resistor (Pin 14) and the compensation

capacitor (Pin 12). Note the use of the 2.5 kΩ bias current

compensation resistors in these examples. These resistors

perform the identical function in the ±1 gain case. Figure 30

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 suppressed 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.

Figure 28. AD630 Configured as a Gain-of-One Balanced Modulator

Figure 29. AD630 Configured as a Gain-of-Two Balanced Modulator

Figure 30. Gain-of-Two Balanced Modulator Sample Waveforms

BALANCED DEMODULATOR

The balanced modulator topology described in the Balanced

Modulator section also acts as a balanced demodulator if a

double sideband suppressed carrier waveform is applied to

the signal input and the carrier signal is applied to the reference

input. The output under these circumstances is the baseband

modulation signal. Higher order carrier components that can

be removed with a low-pass filter are also present. Other names

for this function are synchronous demodulation and phase-

sensitive detection.

PRECISION PHASE COMPARATOR

The balanced modulator topologies of Figure 28 and Figure 29

can also be used as precision phase comparators. In this case,

an ac waveform of a particular frequency is applied to the signal

input and a waveform of the same frequency is applied to the

reference input. The dc level of the output (obtained by low-

pass filtering) is proportional to the signal amplitude and phase

difference between the input signals. If the signal amplitude is

held constant, the output can be used as a direct indication of

the phase. When these input signals are 90° out of phase, they

are said to be in quadrature and the AD630 dc output is zero.

PRECISION RECTIFIER ABSOLUTE VALUE

If the input signal is used as its own reference in the balanced

modulator topologies, the AD630 acts as a precision rectifier.

The high frequency performance is superior to that which can

be achieved with diode feedback and op amps. There are no diode

drops that the op amp must leap over with the commutating

amplifier.

MODULATED

OUTPUT

SIGNAL

CARRIER

INPUT

OFF ADJ

DIFF

OFF ADJ

AMP A

AMP B

–V

10kΩ

5kΩ

COMP

+VS

–VS

AD630

2.5kΩ

10kΩ

MODULATION

INPUT

MODULATED

OUTPUT

SIGNAL

CARRIER

INPUT

OFF ADJ

DIFF

OFF ADJ

2.5kΩ

AMP A

AMP B

–V

10kΩ

5kΩ

COMP

+VS

–VS

AD630

2.5kΩ

10kΩ

MODULATION

INPUT

20µs

MODULATION

INPUT

CARRIER

INPUT

OUTPUT

SIGNAL

10V

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