AD394 datasheet(11/12 Pages) AD

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AD394

Rev. A | Page 11 of 12

OR’ed with LED indicators as shown. The test limits for each

comparator are programmed by the AD394 VOUT2 and VOUT3

outputs. When the output of the device under testing is within

the limits, both comparators are off and D1 lights. If the output

is above or below the limits, either D4 or D5 lights.

AD394 as a Multiplier and Attenuator

So far, it has been assumed that the reference voltage VREFIN is

fixed. In fact, VREFIN can be any voltage within the range of

−11 V < VREFIN < +11 V. It can be negative, positive, sinusoidal, or

whatever the user prefers. This leads to the name “multiplying

D/A converters” because the output voltage, VOUT, is propor-

tional to the product of the digital input word and the voltage at

the VREFIN terminal.

()

4095

4096

REFIN

OUT

−

D is the fractional binary value of the digital word applied to the

converter. The AD394 multiplies the digital input value by the

analog input voltage at VREFIN for any value of VREFIN up to

22 V p-p. This in itself is a powerful tool. Applications requiring

precision multiplication with minimal zero offset and very low

distortion should consider the AD394 as a candidate. One pop-

ular use for the AD394 is as an audio frequency attenuator. The

audio signal is applied to the VREFIN input and the attenuation

code is applied to the DAC; the output voltage is the product of

the two—an attenuated version of the input. The maximum

attenuation range obtainable utilizing 12 bits is 4096:1 or 72 dB.

Figure 16. AD394 as a Multiplier or Attenuator

AD394 Datasheet(PDF) 11 Page - Analog Devices