CC1020-RTR1 datasheet(46/91 Pages) TI

46 / 91 page

CC1020

SWRS046

Page 46 of 92

13.3. 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).

13.4. 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

to 0Fh and then from 50h to the register

setting that gives the desired output power

(e.g. 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.

14.

Input / Output Matching and Filtering

When designing the impedance matching

network for the

CC1020 the circuit must be

matched

correctly

the

harmonic

frequencies as well as at the fundamental

tone. A recommended matching network is

shown in Figure 25. Component values for

various frequencies are given in Table 21.

Component values for other frequencies

can be found using the SmartRF® Studio

software.

As can be seen from Figure 25 and Table

21, the 433 MHz network utilizes a T-type

filter, while the 868/915 MHz network has

π-type filter topology.

It is important to remember that the

physical layout and the components used

contribute significantly to the reflection

coefficient,

especially

the

higher

harmonics. For this reason, the frequency

response of the matching network should

be measured and compared to the

response of the Chipcon reference design.

Refer to Figure 27 and Table 22 as well as

Figure 28 and Table 23.

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 Chipcon 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

the

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

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