Datasheet

IOUTA1
IOUTA2
16-Bit
DAC
DA[15:0]
DB[15:0]
2y–16y f
DATA
f
DATA
y2–y16
A Gain
A
Offset
FIR5
x
sin(x)
A
cos
sin
y2–y16
+
+/−
IOUTB1
IOUTB2
16-Bit
DAC
B Gain
B
Offset
x
sin(x)
B
sin
cos
+
+
DEMUX
B0021-01
DAC5686
SLWS147F – APRIL 2003 – REVISED JUNE 2009 ............................................................................................................................................................ www.ti.com
Figure 19. Data Path in SSB Mode
Figure 20 shows the DAC5686 interfaced to an RF quadrature modulator. The outputs of the complex mixer
stage can be expressed as:
A(t) = I(t)cos( ω
c
t) – Q(t)sin( ω
c
t) = m(t)
B(t) = I(t)sin( ω
c
t) + Q(t)cos( ω
c
t) = m
h
(t)
where m(t) and m
h
(t) connote a Hilbert transform pair. Upper single-sideband up-conversion is achieved at the
output of the analog quadrature modulator, whose output is expressed as:
IF(t) = I(t)cos( ω
c
+ ω
LO
)t – Q(t)sin( ω
c
+ ω
LO
)t
Flexibility is provided to the user by allowing for the selection of – B(t) out, which results in lower-sideband
up-conversion. This option is selected by ssb in the config_msb register. Figure 21 depicts the magnitude
spectrum along the signal path during single-sideband up-conversion for real input. Further flexibility is provided
to the user by allowing for the inverse of sin to be used in the complex mixer by programming rspect in the
config_usb register. The four combinations of rspect and ssb allow the user to select one of four complex
spectral bands to input to a quadrature modulator (see Figure 22 ).
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