Balanced Modulator/Demodulator

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 instrumentation 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

* 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.

* 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.

* 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.

* 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.

* Laser trimming of the comparator and amplifying channel

offsets eliminate the need for external nulling in most cases.

Applications

* Balanced modulation and demodulation

* Synchronous detection

* Phase detection

* Quadrature detection

* Phase sensitive detection

* Lock in amplification

* Square wave multiplication

* 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