May 25, 2005 6881096C74-B
3-28 Theory of Operation: Transmitter
3.6.1.2 100-Watt Transmitter
The following text discusses the 100-W transmitter.
3.6.1.2.1 RF Power Amplifier (RFPA)
The RFPA consists of three gain stages, which are shown in Figure 3-22.
Figure 3-22. 100-Watt RF Power Amplifier (RFPA) Gain Stages (VHF)
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 “3.6.1.4. Power
Control (for 50W and 100W Transmitter)” on page 3-30 for a detailed explanation of the power
control section.
The 2 mW TX_INJ signal is routed to the U3500 first-stage device (Pin 16, RFIN) via C3500 to an
integrated, wide-band input match. U3550 is a two-stage LDMOS device with a bandpass interstage
match consisting of C3502 and L3501 routed between VD1 (pin 14) and G2 (pin 11). L3501 and
L3500 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 U3500 stages are operated Class A.
Driver Stage
C3521, L3520, C3520, and a transmission line form a low-pass, interstage match that transfers
power to the Q3520 LDMOS transistor. R3520-5 provide device stability, and R3526 and C3522
supply the VGBIAS2 gate bias. L3521, R3528, C3525, C3524, C3536, L3522 and R3527 form the
A+ drain bias circuit. Q3520 is operated Class AB.
50W
RFPA_out
100W
50W
Q3540
Q3541
Q3520
10W
5W
A+
A+
A+
Vg_bias
Vg_bias
Vg_bias
100mW
RFPA_cntrl
Tx_inj
2mW
Key9.1V
U3500
30C65
5W
To Next Page
Loading...
Need help?
General