Datasheet

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B0046-01
TRF3701
TRF3702
GND
205 205
15.4
15.4
15.4
15.4
GND
205 205
5 V
50 50
5 V
50 50
B0046-02
AQM
205 205
205 205
5 V
66.5 66.5
5 V
66.5 66.5
0 V
0 V
Nonharmonic Clock-Related Spurious Signals
DAC5687
SLWS164E FEBRUARY 2005 REVISED SEPTEMBER 2006
Figure 68. DAC5687 Passive Interface to TRF3701/2 Analog Quadrature Modulator
Changing the voltage levels and resistor values enables other common-mode voltages at the analog quadrature
modulator input. For example, the network shown in Figure 69 can produce a 3.3-V common mode for the
TRF3703-33, with a 0.96-V
PP
single-ended swing (1.56-V
PP
differential swing).
Figure 69. DAC5687 Passive Interface to TRF3703-33 Analog Quadrature Modulator
In interpolating DACs, imperfect isolation between the digital and DAC clock circuits generates spurious signals
at frequencies related to the DAC clock rate. The digital interpolation filters in these DACs run at subharmonic
frequencies of the output rate clock, where these frequencies are f
DAC
/2
N
, N = 1 3. For example, for X2 mode
there is only one interpolation filter running at f
DAC
/2; for X4 and X4L modes, on the other hand, there are two
interpolation filters running at f
DAC
/2 and f
DAC
/4. In X8 mode, there are three interpolation filters running at f
DAC
/2,
f
DAC
/4, and f
DAC
/8. These lower-speed clocks for the interpolation filter mix with the DAC clock circuit and create
spurious images of the wanted signal and second Nyquist-zone image at offsets of f
DAC
/2
N
.
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