RF2368
Application Notes
Preliminary
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
Gain Select
2.7
2.7
BIAS (V)
0
2.7
VCC1 and VCC2 (V)
2.78
2.78
Current (mA)
1.4
2.2
4
GENERAL PURPOSE
AMPLIFIERS
For both Bypass configurations, the GAIN SELECT pin must be placed at a level greater than or equal to 1.8V. 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 V
CC
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.
5.0V – 2.78V
-------------------------------
= 8.88k
Ω
-
0.25mA
4-202
Rev A0 010503
RFMD [ RF MICRO DEVICES ]
