AD9773

18

PRELIMINARY TECHNICAL DATA

Figure 15. Complex Representation of Two Stage

Upconversion

output = r eal

×

1

com plex baseband

signal

ej(ω 1+ω 2)t

dc

fr equency

1/2

1/2

−ω1-ω2

ω1+ω2

= r eal

Figure 14. Two Stage Upconversion and Resulting Image Rejection

r ea l cha nnel (in)

im a gina r y cha nnel (in)

dc

dc

a

b

rea l

im a gina r y

com plex

m odula tor

out

qua dra ture

m odula tor

r ea l cha nnel (out)

im a gina r y cha nnel (out)

a/2

a/2

fC

-fC*

-

+

fC

-fC

b/2j

- b/2j

b/2

b/2

fC

-fC

fC

-fC

a/2j

- a /2j

to qua dr a tur e

m odula tor

a /4+b/4j

a /4- b/4j

a /4- b/4j

-fQ*

-fQ

fQ

fQ

-f

Q

+f

C

-f

Q

-f

C

f

Q

+f

C

f

Q

-f

C

-

a /4- b/4j a /4+b/4j

- a /4+b/4j

=

-fQ

fQ

a /2- b/2j

r ejected im a ges

*fC = com plex m odulation frequency

a /4+b/4j

- a /4- b/4j

*fQ = quadrature m odulation frequency

a /2+b/2j

In purely complex terms, figure 15 represents the two

stage upconversion from complex baseband to carrier.

In this example,

ω1 and ω2 represent the modulation

frequencies of the digital complex modulator and the

quadrature modulator.

REV. PrA