Texas Instruments TSW3000, Руководство пользователя

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1 Demo Kit Configuration Options
1.1 DAC Component
1.2 VComm Configuration
1.3 VCXO
1.4 VCO
User's Guide
SLWU013A – March 2004 – Revised September 2005
The TSW3000 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 TSW3000 Demo Kit is built for the DAC5687, although this Demo Kit can also support the DAC5686
since 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 3.7 V. In order to
utilize the dc-offset adjustment capabilities of the DAC568x 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 maitained with a passive resistor network that is designed to provide the proper operation
point for the DAC568x and the TRF370x modulator. By design, in order to preserve the proper dc levels,
the DAC gain should be kept at 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 U10 on the back side of the board. 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: Derivativies of 78.6432 (i.e., 157.2864 MHz, 314.5728 MHz)
The VCO 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 RF frequency band of the VCO must be noted in order to know how to program the TRF3750 and
where to measure the output RF signal from the modulator. The typical bands of operation are shown in
Table 1 .
Table 1. Frequency Bands
UMTS PCS GSM900 DCS1800
FREQUENCY 2110-2170 MHz 1930-1990 MHz 935-960 MHz 1805-1880 MHz
SLWU013A – March 2004 – Revised September 2005 7