CC1070
SWRS043A Page 26 of 54
12.4 TX Data Latency
The transmitter will add a delay due to the
synchronization of the data with DCLK and
further clocking into the modulator. The
user should therefore add a delay
equivalent to at least 2 bits after the data
payload has been transmitted before
switching off the PA (i.e. before stopping
the transmission).
12.5 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
CC1070
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, which gives the desired output
power (e.g. C0h for +5 dBm output power
at 868 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.
13 Output Matching and Filtering
When designing the impedance matching
network for the
CC1070
the circuit must be
matched correctly at the harmonic
frequencies as well as at the fundamental
tone. A recommended matching network
is shown in Figure 14. Component values
for various frequencies are given in Table
15. Component values for other
frequencies can be found using the
SmartRF® Studio software.
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 Figure 15 and Table 16 as well as
Figure 16 and Table 17.
A recommended application circuit is
available from the TI web site
(CC1070EM).
Item 433 MHz 868 MHz 915 MHz
C2 2.2 pF, 5%, NP0, 0402 1.5 pF, 5%, NP0, 0402 1.5 pF, 5%, NP0, 0402
C3 5.6 pF, 5%, NP0, 0402 10 pF, 5%, NP0, 0402 10 pF, 5%, NP0, 0402
C60 220 pF, 5%, NP0, 0402 220 pF, 5%, NP0, 0402 220 pF, 5%, NP0, 0402
C71 4.7 pF, 5%, NP0, 0402 3.3 pF, 5%, NP0, 0402 3.3 pF, 5%, NP0, 0402
L2 22 nH, 5%, 0402 6.8 nH, 5%, 0402 6.8 nH, 5%, 0402
L70 47 nH, 5%, 0402 12 nH, 5%, 0402 12 nH, 5%, 0402
L71 47 nH, 5%, 0402 12 nH, 5%, 0402 12 nH, 5%, 0402
R6 82 Ω, 5%, 0402 82 Ω, 5%, 0402 82 Ω, 5%, 0402
Table 15. Component values for the matching network described in Figure 14 (DNM = Do
Not Mount).