adf7023-j Analog Devices, Inc., adf7023-j Datasheet - Page 75

• Manufacturer Part Number: adf7023-j
• Description: High Performance, Low Power, Ism Band Fsk/gfsk/msk/gmsk Transceiver Ic
• Manufacturer: Analog Devices, Inc.

PA/LNA MATCHING
The ADF7023-J has a differential LNA and both a single-ended
PA and differential PA. This flexibility allows numerous
possibilities in interfacing the ADF7023-J to the antenna.
Combined Single-Ended PA and LNA Match
The combined single-ended PA and LNA match allows the
transmit and receive paths to be combined without the use of
an external transmit/receive switch. The matching network
design is shown in Figure 85. The differential LNA match is a
five-element discrete balun giving a single-ended input. The
single-ended PA output is a three-element match consisting of
the choke inductor to the CREGRF2 regulated supply and an
inductor and capacitor series.
The LNA and PA paths are combined, and a seventh-order
harmonic filter provides attenuation of the transmit harmonics.
In a combined match, the off impedances of the PA and LNA
must be considered. This can lead to a small loss in transmit
power and degradation in receiver sensitivity in comparison
with a separate single-ended PA and LNA match. However, with
optimum matching, the typical loss in transmit power is <1 dB,
and the degradation in sensitivity is <1 dB when compared with
a separate PA and LNA matching topology.
CONNECTION
CONNECTION
ANTENNA
ANTENNA
Figure 85. Combined Single-Ended PA and LNA Match
Figure 86. Combined Differential PA and LNA Match
HARMONIC
HARMONIC
FILTER
FILTER
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MATCH
Separate Single-Ended PA/LNA Match
The separate single-ended PA and LNA matching configuration
is illustrated in Figure 84. The network is the same as the combined
matching network shown in Figure 85 except that the transmit and
receive paths are separate. An external transmit/receive antenna
switch can be used to combine the transmit and receive paths
to allow connection to an antenna. In designing this matching
network, it is not necessary to consider the off impedances of
the PA and LNA, and, thus, achieving an optimum match is less
complex than with the combined single-ended PA and LNA match.
Combined Differential PA/LNA Match
In this matching topology, the single-ended PA is not used. The
differential PA and LNA match comprises a five-element discrete
balun giving a single-ended input/output, as illustrated in
Figure 86. The harmonic filter is used to minimize the RF
harmonics from the differential PA.
RX
TX
Figure 84. Separate Single-Ended PA and LNA Match
HARMONIC FILTER
3
4
5
6
3
4
5
6
CREGRF2
RFIO_1P
RFIO_1N
RFO2
ADF7023-J
CREGRF2
RFIO_1P
RFIO_1N
RFO2
ADF7023-J
LNA MATCH
PA MATCH
3
4
5
6
CREGRF2
RFIO_1P
RFIO_1N
RFO2
ADF7023-J
ADF7023-J