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Demonstration Kit Configuration Options
1.1
DAC Component
1.2
VComm Configuration
1.3
VCXO
1.4
LO Generation
Demonstration Kit Configuration Options
The TSW3003 Demonstration (Demo) Kit can be configured in different ways to evaluate different
components in different frequency bands. This section outlines the various component configurations.
Based on the configuration, testing and board setup must be altered to accommodate the given
components and features.
The TSW3003 Demo Kit is built for the DAC5687, although this Demo Kit can also support the DAC5686
because the two devices are pin compatible. The procedures outlined in this document are primarily suited
for the DAC5687, but can be modified easily for the DAC5686 if desired.
The analog quadrature modulator requires a common-mode dc voltage of approximately 3.3 V. In order to
use the dc-offset adjustment capabilities of the DAC5687 for carrier suppression, it is imperative to
maintain a dc path from the DAC output to the modulator input. The common-mode voltage for the
modulator is maintained with a passive resistor network that is designed to provide the proper operation
point for the DAC5687 and the TRF3703 modulator. By design, in order to preserve the proper dc levels,
the DAC coarse gain should be kept at the maximum (15), though deviation by a few steps is generally
acceptable with no degradation in performance.
The CDCM7005 requires a VCXO source to derive its output clock signals. The VCXO is at reference
designator U1. The frequency of the VCXO can be changed to operate the Demo Kit with different
clocking schemes for different modulation standards or for specific customer requirements. Denote which
VCXO frequency is on the board so that the CDCM7005 part can be set up properly. The following
conventions are typically used:
•
WCDMA: Derivatives of 61.44 MHz (i.e., 122.88 MHz, 245.76 MHz, 491.52 MHz)
•
GSM: Derivatives of 52 MHz (i.e., 104 MHz, 208 MHz)
•
CDMA2K: Derivatives of 78.6432 (i.e., 157.2864 MHz, 314.5728 MHz)
The integrated VCO of the TRF3761 outputs the RF signal used for the LO drive on the analog quadrature
modulator. The RF output frequency is contingent on the LO frequency value. The default TRF3761-H
typically has a tuning range from 2028 to 2175 MHz. Other frequency bands will require the existing
TRF3761 to be changed to another pin-compatible part in a different frequency band. Using the TRF3761
internal divider or another TRF3761 part to generate frequencies outside this range requires the output
terminations to be changed. Contact TI for support in this situation.
The RF frequency band of the VCO must be noted in order to know how to program the TRF3761 and at
what frequency to measure the output RF signal from the modulator. The typical bands of operation are
shown in
.
Table 1. Frequency Bands
UMTS
PCS
GSM900
DCS1800
FREQUENCY
2110-2170 MHz
1930-1990 MHz
935-960 MHz
1805-1880 MHz
SLWU029D – October 2006 – Revised August 2007
TSW3003 Demonstration Kit
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