MIPI RF Front-End Control Interface (RFFE) is a dedicated RF front-end component control
interface.
It consists of VIO (pin 57), SCLK (pin 58), and
SDATA (pin 59). VIO is a 1.8 V supply for the MIPI
controller, SCLK is the clock for the controller, and SDATA
is for the control data. The RFFE interface is aligned with the LTE protocol, which enables LTE
protocol synchronous control for nRF9160-external components, such as an antenna tuner.
nRF9160 supports RFFE v1.1 with the following exceptions:
- SCLK is fixed rate 19.2 MHz.
- Only one RFFE component is supported at a time.
- The VIO voltage may be high at any time when nRF9160 is active, not only
when external RFFE components are used.
- The capacitive load of SCLK and SDATA must not exceed
15 pF on the application board.
For noise filtering and diagnostic purposes, it is recommended to add series resistors to
SCLK (R3) and SDATA (R4). In
addition to the series resistor, bypass capacitors (C14, C15, and
C16) in the range of few pF can be considered. They may help to reduce RF coupling to
the RFFE lines. Additional capacitance increases the RFFE load and potentially deteriorates
signal integrity. By default, it is not recommended to assemble capacitors C14,
C15, and C16.
Note: VIO should be assumed to be high when the LTE modem is active. Therefore,
an external RFFE component should not have excessive current leakage at VIO in
any conditions. Typically, VIO consumption or leakage in RFFE components is
very low, but it is recommended to be verified from the component datasheet. External RFFE
components must withstand a situation where VIO is high, but
VDD low. Typically, this is acceptable, but some RFFE components may be more
sensitive than others.
CAUTION:
The combined load of
Printed Circuit Board (PCB) routing, input load of
the RFFE component controller, and parasitic load from the application shall not exceed 15 pF at
nRF9160's
SCLK or
SDATA pins. Typically, this load equals
narrow transmission line length of ≤ 10 cm on the application board, but depends on the actual
PCB design.