Motorola c18, Руководство разработчика

Страница: 22 / 82

Hardware Description
14 98-08901C63-A
The RF output ports are MMCX-type, 50-ohm matched connectors, as follows:
• Cellular antenna connector for 800/1900 MHz and passive aGPS
• GPS antenna connector that supports an aGPS active antenna
3.1.2 RF Block
This section describes the c18 RF block. Figure 4 shows the RF block diagram:
Figure 4. RF Block Diagram
3.1.2.1 Receiver Path
The receiver uses a superhetrodyne architecture, which down-converts to an IF frequency and then to the baseband. The received
signal enters either the passive tri-band antenna, which supports cellular 800 MHz/1900 MHz and aGPS, or the active GPS
antenna, which supplies the required bias voltage for the active antenna circuitry. The signal is directed via the appropriate
duplexer to the programmable RFR3300 IC, where it undergoes preamplification (three LNAs, with one for each band) before
being down-mixed to the IF frequency of 183.6MHz and filtered. From there, the signal enters the IFR3300 IC, where it is
amplified to the required level with AGC circuitry, quadrature down-converted to baseband, filtered and sampled. The sampled
signal is then fed to the DSP section.
3.1.2.2 Transmit Path
The transmitter also uses a superhetrodyne architecture in which the signal is up-converted from baseband to IF and then to the
transmit frequency. The IQ baseband signals enter the RFT3100 IC, which quadrature up-converts to the IF frequency and then
to the transmit frequency using a single side-band up-converter, in order to eliminate the need for expensive IF filtering circuitry.
The signal is amplified to the required power level using the AGC circuitry. The signal is then fed into the power amplifiers via
Tx cleanup filters, which preserve the spectral purity. From there, the signal passes to the appropriate duplexer. The signal then
enters the power detection circuitry, which comprises a directional coupler and a detector. The power detection circuitry feeds
voltage proportional to the transmitted signal power back to the logic circuitry, thereby enabling proper power control.
Power
Detector
IFR3300 Rx
IF
Base
Band
RFT3100
PA Drivers
Ref Osc.
19.2MHz
Cell PA
PCS PA
Rx LO
Tx LO
VCO +
Loop Filter
IF VCO tank
& Loop Filter
Power control
I/Q
I/Q
Active GPS
Ant (alt)
Vcc
Cellular
PCS
GPS
3
Duplexers
RFR3300
Rx FE
Dual
Synth.
Tri- Band
Ant.