X9470 datasheet(17/25 Pages) XICOR

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REV 11.16 3/20/03

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Preliminary Information

X9470

State 3: PA Standby Mode, DC Bias Adjustment

[Compensation for VGS Drift and Temperature

Variation]

When the Power Ampliﬁer is in Standby Mode the

X9470 allows for dynamic adjustment of the DC bias-

ing point to take into account both VGS drift and tem-

perature variation. Dynamic biasing is achieved with

the X9470 by using the CS, and SCL pins. For exam-

ple, the SCL pin can be a steady clock and the CS pin

can be used as a control signal to enable/disable the

Bias Adjustment Block.

Figure 6 illustrates how the X9470 can be used for

dynamic biasing. Upon the presence of an RF signal,

the CS pin is pulled LOW. This will prevent the X9470

from changing the VBIAS voltage during IDQ peak cur-

rents. Once the RF signal is no longer present, the CS

pin can be enabled (closed loop), SDA high and the

X9470 Bias Adjustment Circuit moves the VBIAS volt-

age (the gate voltage of the FET) to meet the average

IDQ bias point for optimum ampliﬁer performance.

State 4: Power Off Mode

During power saving or power-off modes the X9470

can be shut down via the SHDN pin. This pin pulls the

output of the VBIAS pin LOW.

X9470 Datasheet(PDF) 17 Page - Xicor Inc.