RF2368 datasheet(4/8 Pages) RFMD

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Preliminary

4-202

RF2368

Rev A0 010503

Application Notes

Bypass Mode Configurations

The RF2368 may be placed into either high gain or bypass mode via the GAIN SELECT pin (pin 8). The high gain state

is selected by asserting the GAIN SELECT pin to a voltage level of less than 0.8V. For Bypass operation, there are two

possible methods for placing the RF2368 into this low gain state. The table below shows the two possible Bypass config-

urations.

Bypass Mode Possibilities

For both Bypass configurations, the GAIN SELECT pin must be placed at a level greater than or equal to 1.8 V. The dif-

ference between the Bypass possibilities is determined by the specific application's ability to change the voltage of the

BIAS pin (pin 1) independently of the VCC supply voltage. The advantage of the ability to assert the power down pin to

0V when in Bypass mode is shown by the decreased current draw when in this Bypass configuration.

BIAS Pin Resistor

The BIAS pin (pin1) of the RF2368 should be maintained at 2.7V to 2.86V for proper high gain operation. This voltage

range ensures the correct bias current will be present at the BIAS pin of the device. However, an external series resistor

may be used to allow various operating voltages at this pin (see R1 of the evaluation board schematic). The required

value for this resistor may be roughly calculated by using the operating input voltage to the BIAS pin, the desired voltage

at the device, and the typical current consumption for the BIAS pin, along with Ohm's law.

For example, assume the design will supply 5.0V to the BIAS pin of the device, but the biasing circuitry internal to the

RF2368 requires 2.78V typical, and the BIAS current is known to typically be 0.25mA, then the required value for R1

would be found as follows.

Gain Select

BIAS (V)

VCC1 and VCC2 (V)

Current (mA)

2.7

2.78

1.4

2.7

2.78

2.2

5.0V

2.78V

–

0.25mA

--------------------------------

8.88k

Ω

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