Analog Devices Inc.

Category: RF and Microwave

The AD630 is a high precision balanced modulator/demodulatorthat combines a flexible commutating architecture with theaccuracy and temperature stability afforded by laser wafer trimmedthin film resistors. A network of on-board applications resistorsprovides precision closed-loop gains of ±1 and ±2 with 0.05%accuracy (AD630B). These resistors may also be used to accuratelyconfigure multiplexer gains of 1, 2, 3, or 4. External feedbackenables high gain or complex switched feedback topologies.The AD630 can be thought of as a precision op amp with twoindependent differential input stages and a precision comparatorthat is used to select the active front end. The rapid responsetime of this comparator coupled with the high slew rate and fastsettling of the linear amplifiers minimize switching distortion.The AD630 is used in precision signal processing and instrumentationapplications that require wide dynamic range. Whenused as a synchronous demodulator in a lock-in amplifierconfiguration, the AD630 can recover a small signal from100 dB of interfering noise (see the Lock-In AmplifierApplications section). Although optimized for operation up to1 kHz, the circuit is useful at frequencies up to several hundredkilohertz.Other features of the AD630 include pin programmable frequencycompensation; optional input bias current compensationresistors, common-mode and differential-offset voltage adjustment,and a channel status output that indicates which of thetwo 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

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