Design Tips to use Vcntl pin
Power Amplifier Control Using Vcntl
Pin on ACPM-7833
Power amplifier control scheme
in CDMA systems is one of the
important and challenging
aspects of CDMA-based handset
design. Handset designers must
balance maintaining adequate
linearity while optimizing
efficiency at high, medium and
low output power levels. The
primary method to achieve these
goals is to adjust the bias of the
PA as a function of output power.
Theoretically, the best efficiency
would be achieved when the bias
of the PA is continually adjusted
based on the output power
1. Fixed Bias Control
Using a fixed bias point on the
PA is the traditional method, and
it is the simplest. For example,
the recommended value of the
fixed control voltage on the Vcntl
pin for the ACPM-7833 is 2.5V.
The Vcntl pin on the PA is
controlled by PA_ON pin of the
baseband IC. When PA_ON is
HIGH, the output RF signal of the
PA is enabled, enabling the
subscriber unit to transmit the
required data. The switch circuit
also controls the on/off state of
the PA.
requirement of the PA. However,
implementing this type of circuit
can be complex and costly.
Below is an example of how to
control the the output of the PA
using PA_ON and Vcntl pins.
Therefore several different
approaches have been developed
to provide an acceptable trade-
off between optimum efficiency
and optimum manufacturability.
This application section reviews
four methods of controlling the
bias of a CDMA power amplifier:
fixed, step, logical and dynamic.
Power Mode
Shut Down
High Power
PA_ON
LOW
Vcntl
Power Range
—
0V
HIGH
2.5V
≤ 28.5 dBm
Battery
Vbias
Vdd2
Vdd1
Vcntl
To Duplexer
Baseband
IC
PA
TxIC
Enable
PA_ON
Switch Circuit for PA
Vcntl
Note: PMIC: Power Management IC
LDO: Low Drop Output (Regulator)
PMIC or LDO
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