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 V
REF
B, then the output
from DAC B, V
OUT
B, can be expressed as:
V
OUT
B = D
A
× D
B
× V
REF
A
where D
A
and D
B
are the fractional representations of the digital
words in DAC Latch A and DAC Latch B, respectively.
If D
A
= D
B
= D, the result is D
2
× V
REF
A.
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 = −(x
4
+ 2x
3
+ 3x
2
+ 2x + 4) × V
IN
where x is the digital code that is applied to all four DAC
latches.
*DIGITAL INPUTS OMITTED FOR CLARITY.
100kΩ
Y
V
OUT
AV
REF
A
V
OUT
BV
REF
B
V
OUT
CV
REF
C
V
OUT
D
V
REF
D
V
SS
AGND
DGND
15V
V
DD
AD7225*
V
IN
100kΩ
50kΩ
33kΩ
50kΩ
25kΩ
00986-024
Figure 24. Complex Waveform Generation
