User Manual

datasheet
Version 0.9
2017-09-13
deRFsamR21E-23S00/-23S20 datasheet
www.dresden-elektronik.de
Page 25 of 36
RF switches to PA, LNA and antenna
The switch must have 50 Ω inputs and outputs for the RF signal. The switch control can be
realized with the DIG3 and DIG4 signal of the radio transceiver.
Power amplifier (PA)
The PA has to be placed on the TX path after the RF switch. It is important to regard the
PA’s manufacturer datasheet and application notes, especially for designing the power
supply and ground areas. A poor design could cause a very poor RF performance. For
energy efficiency it is useful to activate the PA only during TX signal transmission. In this
case the DIG3 signal can be used as switch for (de-)activating the PA. Some PAs have the
possibility to set them into sleep state. This application can be realized via a dedicated GPIO
pin.
Band-pass filter (BPF)
The use of a band-pass filter is optional. It depends on the PA properties. Some PAs have an
internal BPF and other do not have. The BPF is necessary to suppress spurious emissions of
the harmonics and to be compliant with national EMI limits. It is possible to use an integrated
BPF part or discrete parts. The advantage of the first variant is that the BPF characteristic is
known and published in the manufacturer’s datasheet.
Low noise amplifier (LNA)
The LNA can be used to amplify the received signal. Please refer to the manufacturer’s
datasheet for a proper design. The control can be done by DIG4 signal.
RF switch for antenna diversity
The switch must have 50 Ω inputs and outputs for the RF signal. It is possible to use a
separate switch with 2 inputs and 2 outputs or use another (third) switch following the switch
required for the PA/LNA. Antenna diversity switching can be controlled via DIG1.
Certification
The customer has to ensure, that custom front-end and antenna diversity designs based on
the radio module deRFsamR21E-23S20 meet all national regulatory requirements of the
assignment location and to have all necessary certifications, device registration or
identification numbers.