June 15, 2005
6815854H01-A
3-42
Theory of Operation:
Transmitter
First Stage
The RFPA first stage provides gain that is determined by the control voltage, RFPA_CNTRL. This
control voltage is generated in the power control section and is a function of the final-stage output
power, temperature, and current, as well as the control and A+ voltage levels. See
on
for a detailed explanation of the power control section.
The 2 mW TX_INJ signal is routed to the U6500 first-stage device (Pin 16, RFIN) via C6501 to an
integrated, wide-band input match. U6500 is a two-stage LDMOS device with a bandpass interstage
match consisting of L6502, C6506, and C6503 routed between VD1 (pin 14) and G2 (pin 11). L6501
and L6500 provide the K9.1V drain bias voltage for the first and second stages to VD1 (pin 14) and
RFOUT1/2 (pins 6 and 7), respectively. The RFPA_CNTRL gate bias is provided to both stages
internally via VCNTRL (pin 1). Both U6500 stages are operated Class A, and the second-stage
output power is approximately 200 mW.
Driver Stage
C6502, C6509, C6510, C6511, and a transmission line form a low-pass, interstage match that
transfers power to the Q6520 LDMOS transistor. R6521-5 provide device stability, and R6520 and
C6500 supply the VGBIAS1 gate bias. L6521-2, R6526-7, and C6521-5 form the A+ drain bias
circuit. Q6520 is operated Class AB, and its output power is approximately 4 W.
Final Stage
C6541-2, C6544-5, C6547-8, and transmission lines form a bandpass, splitter match that transfers
power to the LDMOS final-stage transistors Q6540 and Q6541. R6550-3, R6554-7, C6565-6, and
R6559-60 provide stability for Q6540 and Q6541, respectively. R6540 and C6540 supply the
VGBIAS1 gate bias to Q6540. R6543 and C6558 supply the VGBIAS2 gate bias to Q6541. L6542-3,
C6559-60, and R6544 form the A+ drain bias circuit.
C6549-57 and transmission lines form a low-pass, combiner match that transfers approximately
42 W to the antenna switch. Both Q6540 and Q6541 operate Class AB.
R6545-6, C6564, and U6541 comprise the final-stage, current-sense circuit that generates the
VCURRENT voltage proportional to the final stage current. R6546 sets the circuit gain. U6540
generates the VTEMP voltage, which is proportional to the final-stage temperature.
3.12.4.1.2 Output Network (ON)
The ON consists of the antenna switch, harmonic filter, and power detector (see
).
Figure 3-32. Output Network Components (700–800 MHz)
RFPA_OUT
ANTENNA
SWITCH
H-FILTER
POWER
DETECTOR
RF
CONNECTOR
From
RFPA
42W
K9.1V
VREVERSE
VFORWARD
J6700
38.5W
RX_IN
MAEPF-27888-O
Содержание XTL 1500
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