AD7225LP datasheet(18/24 Pages) AD

18 / 24 page

AD7225

Rev. C | Page 18 of 24

less, there exists a good correlation with the actual performance

of the transversal filter (see Figure 23).

DIGITAL WORD MULTIPLICATION

Because each DAC of the AD7225 has a separate reference input,

the output of one DAC can be used as the reference input for

another. This means that multiplication of digital words can be

performed (with the result given in analog form). For example,

if the output from DAC A is applied to VREFB, then the output

from DAC B, VOUTB, can be expressed as:

VOUTB = DA × DB × VREFA

where DA and DB are the fractional representations of the digital

words in DAC Latch A and DAC Latch B, respectively.

If DA = DB = D, the result is D2 × VREFA.

In this manner, the four DACs can be used on their own or in

conjunction with an external summing amplifier to generate

complex waveforms. Figure 24 shows one such application.

In this case, the output waveform, Y, is represented by

Y = −(x4 + 2x3 + 3x2 + 2x + 4) × VIN

where x is the digital code that is applied to all four DAC

latches.

*DIGITAL INPUTS OMITTED FOR CLARITY.

100k

Ω

VOUTA

VREFA

VOUTB

VREFB

VOUTC

VREFC

VOUTD

VREFD

VSS

AGND DGND

15V

VDD

AD7225*

VIN

100k

Ω

50k

Ω

33k

Ω

50k

Ω

25k

Ω

Figure 24. Complex Waveform Generation

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