Operating instructions

Section 6
800/900 BAND (806–941 MHZ) INFORMATION
1.0 Transmitter
Figure 6-1: 800/900 Transmitter Block diagram
1.1 General
The transmitter contains five basic circuits:
1. Power Amplifier
2. Antenna Switch
3. Harmonic Filter
4. Antenna Matching Network
5. Power Control
1.1.1 Power Amplifier
The power amplifier is a 3-stage discrete design consisting of:
1. Pre-driver, ADA4743 (U700)
2. Driver, RD01MUS1 (Q703)
3. Final PA, RD05MMP1 (Q704)
The pre-driver is a 50 Ohm gain block with a supply voltage of 5V. The gate bias is ramped to
eliminate feed-through power due to the fixed gain of the device. The pre-driver is biased in Class A
region with a typical current drain of 60mA and power gain of 16.5dB.
The driver is a 1W, LDMOS in a SOT-89 package. this stage typically drains 150mA of current at rated
output power, 2.8W at the antenna. The driver is biased in Class AB region and has a power gain of
10dB.
The final PA is a 5.5W, LDMOS device. The gate threshold of this device is very close to the driver.
Hence, the traditional PA bias tuning is eliminated. The current drain would typically be 1300mA. The
final PA is biased in Class AB region and has a power gain of 8dB.
PA
Pre
-
Driver
PA
Drive
r
PA
F
inal
A
nten na Switch/
Harmonic Filter/
Matching Network
Powe
r
Control
A
ntenna
Jack
F
rom VCO
Vcontrol Vcontrol