Texas Instruments TRF3703, User Manual, Page: 7 / 22

C003
1.4.1.2 Optimized Sideband Suppression
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Overview
Figure 1. Un-Optimized Sideband Suppression
There are two ways to change the sideband suppression of the TRF3703. One is the amplitude between
the four inputs, and the second is the phase of the four inputs. The ideal condition is when all four inputs
(I, I, Q, and Q) have exactly the same amplitude and the phase relationship is: I = 0
°
, I = 180
°
, Q = 90
°
,
and Q = 270
°
. Also, the optimization of the sideband is controlled by the amplitude and phase of the I and
Q signals, which are controlled with the gain settings of the DAC. This is an iterative procedure that results
in optimized suppression levels that exceeds 60 dBc. The level of suppression observed depends on the
amount of resolution available from the DAC driving the modulator. By using TI’s DAC568X, the user can
take advantage of built-in features (DAC fine gain) to optimize the sideband suppression by changing the
amplitude relationship of the signals. If another DAC is used, then the user must provide this level of
adjustment by controlling the regular digital inputs to the DAC. See
Figure 2 .
SLWU042B – October 2006 – Revised August 2008 TRF3703 Quadrature Modulator Evaluation Module 7
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