RF5755 Datasheet, PDF (11/15 Pages) RF Micro Devices – 2.4GHz TO 2.5GHz 802.11b/g/n WiFi FRONT END MODULE

RF5755
WiFi and BLUETOOTH^® RECEIVE (SIMULTANEOUS MODE)
The RF755 WiFi and Bluetooth^® receive circuits were specifically designed to address issues of simultaneous operation. In this
mode both signals can be received at the same time when the C_BWRX (pin-16) is set high. The typical gain for each RF path is
approximately 13dB and a NF of 3dB. During simultaneous mode the active components are the LNA, the SPST switch, and
only the Rx branch of the SP3T. Refer to the logic control table for proper settings.
Simultaneous Mode Biasing Instructions
• Connect the RF input (ANT/pin-11) to a signal generator and a spectrum analyzer at the RX (pin-2) and BT (pin-13) RF
ports. A multiport VNA may be used as well.
• Turn the LNA bias on (pin-1) and set the voltage to 3.3V.
• Set C_RX (pin-15) and C_BWRX (pin-16) high. This turns on the receive branch of the SP3T and the SPST switch.
• The SP3T controls for the off branches (V_REG and C_BT) must be set to a logic “low” (0.2V max) or grounded. In the event
that one of these branches is left floating or in a logic “high” the performance will degrade. It is recommended to termi-
nate unused RF Ports in 50Ω.
• Turn RF on.
BLUETOOTH^® MODE
The RF755 Bluetooth^® only mode is implemented through the SP3T switch by setting C_BT “high.” Typical insertion loss is
about 1.2dB.
Bluetooth^® Biasing Instructions
• Connect the RF input (ANT/pin-11) to a signal generator and a spectrum analyzer at the BT (pin-13) RF port. A VNA
may be used in place of the signal generator and SA.
• Set C_BT (pin-12) “high.” This turns the Bluetooth^® branch of the SP3T switch on.
• The SP3T controls for the off branches (V_REG and C_RX) must be set to a logic “low” (0.2V max) or grounded. Do not
leave floating.
• Terminate unused RF Ports in 50Ω.
• Turn RF on.
APPLICATION CIRCUIT AND LAYOUT RECOMMENDATIONS
The RF5755 integrates the matching networks and DC blocking capacitors for all RF ports. This greatly reduces the number of
external components and layout area needed to implement this FEM. Typically only a total of four external components are
required to achieve nominal performance. However, depending on board layout and the many noise signals that could poten-
tially couple to the RF5755, additional bypassing capacitors may be required to properly filter out unwanted signals that might
degrade performance.
The LNA bias components consist of an inductor and a decoupling capacitor. The inductor value is critical to optimize NF and
return loss at the Rx output. For best performance and trade off between critical parameters such as NF, Gain, and IP3, the
total inductance including board trace should be approximately 1.2nH. The 5.6kΩ series resistor for the Bluetooth^® control
line helps to prevent unwanted signals from coupling to this pin. The resistor should be placed as close as possible to the pack-
age pin. The last component needed in the application circuit is a low frequency bypass capacitor on the V_CC line. In general, it
is good RF practice to have proper decoupling of supply lines to filter out noise. Occasionally, depending on the level of cou-
pling or parasitics of the board, a high frequency bypass capacitor must be added as well.
In order to optimize performance for both the Transmit and Receive paths, a good layout design must be implemented. As it is
well know in the RF world, any mismatch and off port loading affects performance. To minimize this effect and have a more
robust layout, all RF traces must be 50Ω. Adequate grounding along the RF traces and on the FEM ground slug must be exer-
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