3-12 Theory of Operation: Main Board
Figure 3-12. Transmitter Block Diagram (700/800 MHz)
3.1.3.1 Driver Amplifier
The driver amplifier IC (VHF – U902, UHF1/UHF2 – U1602, 700/800/900 MHz – U1002) contains
one LDMOS FET amplifier stages and an internal resistor bias networks. Pin 16 is the RF input.
Modulated RF from the FGU, at a level of +3 dBm ±2 dB, is coupled through a blocking capacitor to
the gate of
FET-1. An LC inter-stage matching network connects the first stage output VD1 to the second stage
input G2. The RF output from the drain of FET-2 is pin 6 (RFOUT1). Gain control is provided by a
voltage applied to pin 1 (VCNTRL). Typical output power is about +27 dBm (500 mW) with VCNTRL
at 5.5 V.
VHF: L901 and C904 is the inter-stage matching network of the driver amplifier IC, C907, C910,
L904, C913, C914, L905 and C916 serves as matching circuit of the driver IC to the final device of
Q901. Capacitor C907 also works as DC block to the circuit.
UHF1/UHF2: L1601 and C1604 is the inter-stage matching network of the driver amplifier IC, C1607,
C1610, L1604, C1613, C1614, L1605 and C1616 serves as matching circuit of the driver IC to the
final device of Q1601. Capacitor C1607 also works as DC block to the circuit.
700/800/900 MHz: L1002, C1002 and C1004 are the inter-stage matching network. Components
C1013 and C1023 match the output impedance to the input of the final device (Q1001); capacitor
C1013 also serves as the DC block.
S
Trident IC
Synthesizer
Loop Filter
700 MHz
VCO
7/800 MHz
VCO
RF Switch Matrix
TX Buffer Amp
TX Driver Amplifier
Transmitter Final
FET 7/800 MHz
Harmonic
LP Filter
Ref. Oscillator
Antenna Connector
Directional
Coupler
Antenna
Switch
TO RX
GPS
Reverse Power
Detection
Log Amp Power Detector
Digital RF Attenuator
800 MHz
VCO
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