User's Manual

User Manual
Version 1.1c
2013-07-01
OEM radio modules deRFmega
www.dresden-elektronik.de
Page 44 of 52
10.5. External front-end and antenna diversity
The radio module deRFmega128-22M10 can be connected with an external front-end
including power amplifier (PA) for transmission and low noise block (LNA) for receiving.
Figure 40 shows a possible design as block diagram. A custom design can contain a single
PA or single LNA or a complete integrated front-end chip. It depends mainly on the
application. Furthermore, it is possible to include a RF switch for driving the antenna diversity
feature.
deRFmega128
22M10
VCC
1.8V to 3.6V
GPIO
for PA on/off
PA
LNA
RF switch RF switch
BPF
RFout
ANT0
ANT1
DIG3
DIG4
DIG1
Figure 40: block diagram for external PA/LNA and antenna diversity control
Unbalanced RF output
The radio module 22M10 has a 50 Ω unbalanced RF output. For designs with external RF
power amplifier a RF switch is required to separate the TX and RX path.
RF switches to PA, LNA and antenna
The switch must have 50 Ω inputs and outputs for the RF signal. The switch control could be
realized with the DIG3 and DIG4 signal of the radio module. Refer to Section 7.2.1 for
detailed information.
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. Refer to Section 7.2.1 for more information.
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.