Balanced Modulator/Demodulator

Data Sheet

AD630

Rev. G

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FEATURES

Recovers signal from 100 dB noise

2 MHz channel bandwidth

45 V/µs slew rate

Low crosstalk: −120 dB at 1 kHz, −100 dB at 10 kHz

Pin programmable, closed-loop gains of ±1 and ±2

0.05% closed-loop gain accuracy and match

100 µV channel offset voltage (AD630)

350 kHz full power bandwidth

Chips available

APPLICATIONS

Balanced modulation and demodulation

Synchronous detection

Phase detection

Quadrature detection

Phase sensitive detection

Lock in amplification

Square wave multiplication

FUNCTIONAL BLOCK DIAGRAM

Figure 1.

GENERAL DESCRIPTION

The AD630 is a high precision balanced modulator/demodulator

that combines a flexible commutating architecture with the

accuracy and temperature stability afforded by laser wafer trimmed

thin film resistors. A network of on-board applications resistors

provides precision closed-loop gains of ±1 and ±2 with 0.05%

accuracy (AD630B). These resistors may also be used to accurately

configure multiplexer gains of 1, 2, 3, or 4. External feedback

enables high gain or complex switched feedback topologies.

The AD630 can be thought of as a precision op amp with two

independent differential input stages and a precision comparator

that is used to select the active front end. The rapid response

time of this comparator coupled with the high slew rate and fast

settling of the linear amplifiers minimize switching distortion.

The AD630 is used in precision signal processing and instru-

mentation applications that require wide dynamic range. When

used as a synchronous demodulator in a lock-in amplifier

configuration, the AD630 can recover a small signal from 100 dB

of interfering noise (see the Lock-In Amplifier Applications

section). Although optimized for operation up to 1 kHz, the

circuit is useful at frequencies up to several hundred kilohertz.

Other features of the AD630 include pin programmable frequency

compensation; optional input bias current compensation resistors,

common-mode and differential-offset voltage adjustment, and a

channel status output that indicates which of the two differential

inputs is active.

PRODUCT HIGHLIGHTS

1. The application flexibility of the AD630 makes it the best

choice for applications that require precisely fixed gain,

switched gain, multiplexing, integrating-switching

functions, and high speed precision amplification.

2. The 100 dB dynamic range of the AD630 exceeds that of

any hybrid or IC balanced modulator/demodulator and is

comparable to that of costly signal processing instruments.

3. The op amp format of the AD630 ensures easy implementation

of high gain or complex switched feedback functions. The

application resistors facilitate the implementation of most

common applications with no additional parts.

4. The AD630 can be used as a 2-channel multiplexer with gains

of 1, 2, 3, or 4. The channel separation of 100 dB at 10 kHz

approaches the limit achievable with an empty IC package.

5. Laser trimming of the comparator and amplifying channel

offsets eliminate the need for external nulling in most cases.

CM OFF

ADJ

CM OFF

ADJ

DIFF OFF

ADJ

DIFF OFF

ADJ

2.5kΩ

AMP A

2.5kΩ

AMP B

–V

10kΩ

10kΩ

5kΩ

COMP

CH A+

CH A–

CH B+

CH B–

SEL B

SEL A

COMP

CHANNEL

STATUS

B/A

A

B

BIAS