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CC1021
RF_OUT
RF_IN
C60
R10
L2
C3
L1
C1
C71
C72
L70
L71
T/R
SWITCH
AVDD = 3 V
ANTENNA
SWRS046H – NOVEMBER 2006 – REVISED MARCH 2015
5.10.4 Reducing Spurious Emission and Modulation Bandwidth
Modulation bandwidth and spurious emission are normally measured with the PA continuously on and a
repeated test sequence.
In cases where the modulation bandwidth and spurious emission are measured with the CC1020
switching from power down mode to TX mode, a PA ramping sequence could be used to minimize
modulation bandwidth and spurious emission.
PA ramping should then be used both when switching the PA on and off. A linear PA ramping sequence
can be used where register PA_POWER is changed from 00h to 0Fh and then from 50h to the register
setting that gives the desired output power (for example, F0h for +10 dBm output power at 433 MHz
operation). The longer the time per PA ramping step the better, but setting the total PA ramping time equal
to 2 bit periods is a good compromise between performance and PA ramping time.
5.11 Input and Output Matching and Filtering
When designing the impedance matching network for the CC1020 the circuit must be matched correctly at
the harmonic frequencies as well as at the fundamental tone. A recommended matching network is shown
in
. Component values for various frequencies are given in
. Component values for
other frequencies can be found using the SmartRF Studio software.
As can be seen from
and
, the 433 MHz network utilizes a T-type filter, while the
868/915 MHz network has a
π
-type filter topology.
It is important to remember that the physical layout and the components used contribute significantly to
the reflection coefficient, especially at the higher harmonics. For this reason, the frequency response of
the matching network should be measured and compared to the response of the TI reference design.
Refer to
and
as well as
and
The use of an external T/R switch reduces current consumption in TX for high output power levels and
improves the sensitivity in RX. A recommended application circuit is available from the TI web site
(CC1020EMX). The external T/R switch can be omitted in certain applications, but performance will then
be degraded.
The match can also be tuned by a shunt capacitor array at the PA output (RF_OUT). The capacitance can
be set in 0.4-pF steps and used either in RX mode or TX mode. The RX_MATCH[3:0] and
TX_MATCH[3:0] bits in the MATCH register control the capacitor array.
Figure 5-22. Input and Output Matching Network
42
Detailed Description
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