MC13201 Technical Data, Rev. 1.3,
Freescale Semiconductor 25
Table 10 summarizes the operation of the RF interface control bits.
8.7 RF Control Output CT_Bias
CT_Bias is a useful signal for interface with external RF components. It must be enabled via the ct_bias_en
control bit, and then its state is determined first by the selected RF mode and then by the active state of the
radio, i.e., whether a TX or RX operation is active:
• Single Port Operation - In this mode, the CT_Bias can be used to establish the proper DC bias
voltage to a balun depending on the RX state versus TX state as described in Section 8.5.1, “Single
Port Operation. Note that in single port operation, the ct_bias_inv has no effect and CT_Bias is at
VDDA for TX and is at ground for RX.
• Dual Port Operation - In this mode, the CT_Bias can be used as a control signal to enable a LNA
or PA or to determine the direction of an antenna switch as described in Section 8.5.2, “Dual Port
Operation. In dual port operation, ct-bias_inv is used to control the sense of the output control, i.e.,
CT_Bias can be active high or active low for TX and vice-versa for RX.
Table 11 defines the CT_Bias output state depending on control bits and operation mode of the modem.
Note that the output state is also defined in Idle, Hibernate, and Doze state as well as RX and TX operation.
Table 10. RF Interface Control Bits
Bit Designation Default Operation
14 ct_bias_en 0 1 = CT_Bias enabled. Output state is defined by Table 11.
0 = CT_Bias disabled. Output state is tri-stated.
13 ct_bias_inv 0 The output state of CT_Bias under varying conditions is defined in Table 11. This bit only
has effect for dual port operation.
1 = CT_Bias inverted.
0 = CT_Bias not inverted
12 RF_switch_mode 0 1= Single Port Mode selected where RF switch is active and RFIN_M and RFIN_P and
bidirectional signals.
0 = Dual Port Mode selected where RFIN_M and RFIN_P are inputs only and PAO_P
and PAO_N are separate outputs.
(This is default operation).
Table 11. CT_Bias Output vs. Register Settings
Mode CT_Bias_en RF_switch_mode CT_Bias_inv CT_Bias
RX 1 1 0 0
RX 1 1 1 0
RX 1 0 0 0
RX 0 X X Hi-Z
RX 1 1 0 1
TX 1 1 0 1
TX 1 1 1 1
TX 1 0 0 1
