2. Step Bias Control and Dynamic
Bias Control (if controled PDM1)
The PDM1 output from the
baseband IC can be used to
create a software-programmable
voltage, to be used at the phone
designer’s discretion. To get high
efficiency and better ACPR, the
phone designers can change
control voltage of the PA by
adjusting PDM1 voltage accord-
ing to output power of PA. A
caution when using this
approach—careful consideration
must be made to to avoid an
abrupt discontinuity in the
output signal when the step bias
control voltage is applied.
The figure below is an example of
how to control the PA for
multiple bias points using the
PA_ON and Vcntl pins.
Power Mode
Shut Down
Low Power
Mid Power
High Power
PA_ON
LOW
Vcntl
Power Range
—
0V
HIGH
HIGH
HIGH
1.2V
1.6V
2.5V
~ -5 dBm
-5 dBm ~ 13 dBm
13 dBm ~ 28.5 dBm
Battery
Vbias
Vdd2
Vdd1
To Duplexer
Baseband
IC
PA
TxIC
Vcntl
PA_ON
PDM1
Enable
R1
Switch Circuit for PA
C1
If PDM1 can be controlled then same circuit can be used for Dynamic bias control
12
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