System Considerations
MC1321x Reference Manual, Rev. 1.6
Freescale Semiconductor
3-19
3.10.1.1
Single Port Operation
The integrated RF switch allows users to operate in a single port configuration. In Single Port Mode, an
internal RX switch and separate PA are used and pins RFIN_P (PAO_P) and RFIN_M (PAO_M) become
bidirectional and connect both for TX and RX. When receiving, the RX switch is enabled to the internal
LNA and the TX PA1 is disabled. When transmitting, the RX switch is disabled (isolating the LNA) and
TX PA1 is enabled. The optional CT_Bias pin provides a reference or bias voltage which is at VDDA for
transmit and is at ground for receive. This signal can be used to provide the proper bias voltage to a balun
that converts a single-ended antenna to the differential interface required by the SiP.
shows a single port example with a balun. The CT_Bias is connected to the balun center-tap
providing the proper DC bias voltage to the balun depending on RX or TX.
Figure 3-5. Single Port RF Operation with a Balun
3.10.1.2
Dual Port Operation
A second set of pins designated PAO_P and PAO_N allow operation in a dual port configuration. There
are separate paths for transmit and receive with the optional CT_Bias pin providing a signal that indicates
if the radio is in TX or RX Mode which then can be used to drive an external low noise amplifier or power
amplifier.
In dual port operation, the RFIN_P and RFIN_N are inputs only, the internal RX switch to the LNA is
enabled to receive, and the associated TX PA1 stays disabled. Pins PAO_P and PAO_N become the
differential output pins and the associated TX PA2 is enabled for transmit.
shows two dual port configurations. First is a single antenna configuration with an external low
noise amplifier (LNA) for greater range. An external antenna switch is used to multiplex the antenna
between receive and transmit. An LNA is in the receive path to add gain for greater receive sensitivity.
Two external baluns are required to convert the single-ended antenna switch signals to the differential
signals required by the radio. Separate RFIN and PAO signals are provided for connection with the baluns,
and the CT_bias signal is programmed to provide the external switch control. The polarity of the external
switch control is selectable.
also shows a dual antenna configuration where there is a RX antenna and a TX antenna. For the
receive side, the RX antenna is ac-coupled to the differential RFIN inputs and these capacitors along with
Balun
Bypass
RFIN_P (PAO_P)
RFIN_M (PAO_M)
CT_Bias
PAO_P
PAO_M
MC1321x
L1
Содержание freescale semiconductor MC13211
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