AD831 Просмотр технического описания (PDF) - Analog Devices

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AD831

Low Distortion Mixer

Analog Devices 

AD831

APPLICATIONS

Careful component selection, circuit layout, power supply

dc coupling, and shielding are needed to minimize the AD831’s

susceptibility to interference from radio and TV stations, etc. In

bench evaluation, we recommend placing all of the components

in a shielded box and using feedthrough decoupling networks for

the supply voltage.

Circuit layout and construction are also critical, since stray capaci-

tances and lead inductances can form resonant circuits and are a

potential source of circuit peaking, oscillation, or both.

Dual-Supply Operation

Figure 9 shows the connections for dual-supply operation. Supplies

may be as low as ±4.5 V but should be no higher than ±5.5 V, due

to power dissipation.

The RF input to the AD831 is shown connected by an impedance

matching network for an assumed source impedance of 50 .

TPC 15 shows the input impedance of the AD831 plotted vs.

frequency. The input circuit can be modeled as a resistance in

parallel with a capacitance. The 82 pF capacitors (CF) connected

from IFN and IFP to VP provide a low-pass filter with a cutoff

frequency of approximately 140 MHz in down-conversion appli-

cations (see the Theory of Operation section for more details).

The LO input is connected single-ended because the limiting

amplifier provides a symmetric drive to the mixer. To minimize

intermodulation distortion, connect pins OUT and VFB by the

shortest possible path. The connections shown are for unity-gain

operation.

At LO frequencies less than 100 MHz, the AD831’s LO power

may be as low as –20 dBm for satisfactory operation. Above

100 MHz, the specified LO power of –10 dBm must be used.

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Figure 9. Connections for ±5 V Dual-Supply Operation Showing Impedance

Matching Network and Gain of 2 for Driving Reverse-Terminated IF Filter

–10–

REV. C

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