The AD831 is a low distortion, wide dynamic range, monolithicmixer for use in such applications as RF to IF down conversionin HF and VHF receivers, the second mixer in DMR base stations,direct-to-baseband conversion, quadrature modulationand demodulation, and doppler-shift detection in ultrasoundimaging applications. The mixer includes an LO driverand a low-noise output amplifier and provides both user-programmablepower consumption and 3rd-order intercept point.

The AD831 provides a +24 dBm third-order intercept point for-10 dBm LO power, thus improving system performance andreducing system cost compared to passive mixers, by eliminatingthe need for a high power LO driver and its attendant shieldingand isolation problems.

The RF, IF, and LO ports may be dc or ac coupled when themixer is operating from ±5 V supplies or ac coupled when operatingfrom a single supply of 9 V minimum. The mixer operateswith RF and LO inputs as high as 500 MHz.

The mixer's IF output is available as either a differential currentoutput or a single-ended voltage output. The differential outputis from a pair of open collectors and may be ac coupled via atransformer or capacitor to provide a 250 MHz output bandwidth.In down-conversion applications, a single capacitor connectedacross these outputs implements a low-pass filter toreduce harmonics directly at the mixer core, simplifying outputfiltering. When building a quadrature-amplitude modulator orimage reject mixer, the differential current outputs of twoAD831s may be summed by connecting them together.

An integral low noise amplifier provides a single-ended voltageoutput and can drive such low impedance loads as filters, 50 Wamplifier inputs, and A/D converters. Its small signal bandwidthexceeds 200 MHz. A single resistor connected between pinsOUT and FB sets its gain. The amplifier's low dc offset allowsits use in such direct-coupled applications as direct-to-basebandconversion and quadrature-amplitude demodulation.

The mixer's SSB noise figure is 10.3 dB at 70 MHz using itsoutput amplifier and optimum source impedance. Unlike passivemixers, the AD831 has no insertion loss and does not requirean external diplexer or passive termination.

A programmable-bias feature allows the user to reduce powerconsumption, with a reduction in the 1 dB compression pointand third-order intercept. This permits a tradeoff between dynamicrange and power consumption. For example, the AD831may be used as a second mixer in cellular and two-way radiobase stations at reduced power while still providing a substantialperformance improvement over passive solutions.

At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.