ACPM-7833-BLK データシートの表示（PDF） - Avago Technologies
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ACPM-7833-BLK Datasheet PDF : 20 Pages
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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 requirement of
the PA. However, implementing this type of circuit can
be complex and costly. 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.
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.
Below is an example of how to control the the output
of the PA using PA_ON and Vcntl pins.
Power Mode
Shut Down
High Power
PA_ON
LOW
HIGH
Vcntl
0V
2.5V
Power Range
—
- 28.5 dBm
To Duplexer
Vbias
Vdd2
Vdd1 PA
Vcntl
Battery
TxIC
Baseband
IC
Enable
Switch Circuit for PA
Vcntl
PMIC or LDO
PA_ON
Note: PMIC: Power Management IC
LDO: Low Drop Output (Regulator)
11
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