AD9775EB View Datasheet(PDF) - Analog Devices
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Description
Manufacturer
AD9775EB Datasheet PDF : 48 Pages
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The entire upconversion, from baseband to transmit frequency,
is represented graphically in Figure 33. The resulting spectrum
shown in Figure 33 represents the complex data consisting of
the baseband real and imaginary channels, now modulated onto
orthogonal (cosine and negative sine) carriers at the transmit
frequency. It is important to remember that in this application
(two baseband data channels) the image rejection is not
dependent on the data at either of the AD9775 input channels.
AD9775
In fact, image rejection will still occur with either one or both of
the AD9775 input channels active. Note that by changing the sign
of the sinusoidal multiplying term in the complex modulator, the
upper sideband image could have been suppressed while passing
the lower one. This is easily done in the AD9775 by selecting
the e+jt bit (Register 01h, Bit 1). In purely complex terms,
Figure 31 represents the two-stage upconversion from complex
baseband to carrier.
REAL CHANNEL (IN)
A
DC
COMPLEX
MODULATOR
IMAGINARY CHANNEL (IN)
B
DC
REAL CHANNEL (OUT)
A/2
A/2
–FC*
FC
–B/2J
B/2J
–FC
FC
IMAGINARY CHANNEL (OUT)
–A/2J
A/2J
–FC
–FC
B/2
B/2
TO QUADRATURE
MODULATOR
–FC
FC
*FC = COMPLEX MODULATION FREQUENCY
*FQ = QUADRATURE MODULATION FREQUENCY
A/4 + B/4J A/4 – B/4J
A/4 + B/4J A/4 – B/4J
REAL
IMAGINARY
OUT
QUADRATURE
MODULATOR
–FQ*
–FQ – FC
–FQ + FC
–A/4 – B/4J A/4 – B/4J
–FQ
FQ
FQ – FC
FQ + FC
A/4 + B/4J –A/4 + B/4J
FQ
A/2 + B/2J
REJECTED IMAGES
A/2 – B/2J
–FQ
FQ
Figure 33. Two-Stage Upconversion and Resulting Image Rejection
REV. 0
–31–
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