Datasheet

AD9786
Rev. B | Page 41 of 56
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1200100 200 400 600 800 1000
–4
4
3
–1
1
2
–2
–3
0
Figure 76. Phase Response of Hilbert Transform
Table 37. Dual Channel Complex Modulation Sideband Selection
Sideband Mode
0 Upper IF sideband rejected
1 Lower IF sideband rejected
0
90
AD9786
AD9786
LO
I
Q
Im()
Re()
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Figure 77. AD9786 Driving Quadrature Modulator
The AD9786 can be configured to drive a quadrature modulator,
as in Figure 77. When two AD9786s are used with one AD9786
producing the real output, the second AD9786 produces the
imaginary output. By configuring the AD9786 as a complex
modulator coupled to a quadrature modulator, IF image
rejection is possible. The quadrature modulator acts as the real
part of a complex modulation, producing a double sideband
spectrum at the local oscillator (LO) frequency with mirror
symmetry about dc.
A baseband double sideband signal modulated to IF increases
IF filter complexity and reduces power efficiency. If the base-
band signal is complex, a single sideband IF modulation can be
used, relaxing IF filter complexity and increasing power
efficiency.
The AD9786 has the ability to place the baseband single side-
band complex signal either above or below the IF frequency.
Figure 78, Figure 79, and Figure 80 illustrate this.
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0.5–0.5 –0.4 –0.3 –0.2 –0.1 0 0.1 0.2 0.3 0.4
dBFS
–150
0
–50
–100
Figure 78. Upper IF Sideband Rejected
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0.5–0.5 –0.4 –0.3 –0.2 –0.1 0 0.1 0.2 0.3 0.4
dBFS
–150
0
–50
–100
Figure 79. Lower IF Sideband Rejected
00
f
IF
–f
IF
–
f
IF
f
IF
0
–
f
IF
f
IF
BASEBAND IF
SIDEBAND = 1
SIDEBAND = 0
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Figure 80. IF Quadrature Modulation of Real and Complex Baseband Signals