A1101R09x – Users Manual
Page 23 of 26
Release Date 02/10/11
3.5.
Power Supply Considerations
Noise on the power supply line reduces the sensitivity of a receiver and modulates onto a
transmitter’s signal, both of which causes a degradation of link quality and hence a reduction in
range.
The A1101R09A and A1101R09C radio modules each have an integral ferrite bead in the
supply line from pin 18 (Vdd) and decoupling capacitance to reduce any noise on the incoming
power supply line. This arrangement will eliminate most supply voltage noise. In particularly
noisy environments (switching regulators, motor controls, etc.), it may be necessary to add
additional noise reduction means.
Pin 7 (Vdcoup1) is connected to the modules internal supply line after the ferrite bead and
decoupling capacitors and can be used to probe the noise at module level. The noise level
measured on pin 7 should not exceed 120mVpp when in transmit or receive mode; it may
however exceed this value when setting up or accessing data to/from the FIFOs, while not
actively transmitting or receiving.
If the level measured is exceeding the above limit, steps should be taken to ensure maximum
range, including:
•
Adding decoupling capacitance to pin 7 (Vdcoup1).
•
Adding additional filtering in the supply line.
•
Adding an LDO in the supply line (the TPS731xx low Dropout Regulator from TI is
recommended).
