Semtech LR1110 - Direct-Tie Implementation; Figure 9-11: RF Switch, Double PA Operation; Figure 9-12: RF Switch, Single PA Operation (High Power PA Example); Figure 9-13: Single Tie Implementation: Only One PA Used (High Power PA Example)

LR1110
User Manual Rev.1.0
UM.LR1110.W.APP March 2020
81 of 130
Semtech
www.semtech.com
9.4.3 Direct-Tie Implementation
In case of cost-sensitive application, it is possible to get rid of the RF switch, and implement a so-called direct-tie
implementation.
In such a configuration, the PA and the RX differential stages are connected as depicted in the figure hereafter. Please note
that series capacitances are required between the PA and the RX stage in order to avoid damaging the LR1110 due to
current flowing in the RX stage.
Compared to the switched implementation, the direct-tie suffers a trade-off between TX efficiency and RX sensitivity. This
is unavoidable because the transmitter and receiver require different optimal impedances, which may not be
simultaneously feasible. In the case of a direct-tie, the user should expect a degradation of 2 ~ 3 dB in RX sensitivity.
Figure 9-11: RF Switch, Double PA Operation Figure 9-12: RF Switch, Single PA Operation (High
Power PA Example)
Figure 9-13: Single Tie implementation: Only one PA
Used (High Power PA Example)
Figure 9-14: Single Tie implementation: Both PAs
Used (High Power PA Example)
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