CC1070-RTY1 datasheet(26/57 Pages) TI2

26 / 57 page

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

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

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

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

web

site

(CC1070EM).

Item

433 MHz

868 MHz

915 MHz

2.2 pF, 5%, NP0, 0402

1.5 pF, 5%, NP0, 0402

5.6 pF, 5%, NP0, 0402

10 pF, 5%, NP0, 0402

C60

220 pF, 5%, NP0, 0402

C71

4.7 pF, 5%, NP0, 0402

3.3 pF, 5%, NP0, 0402

22 nH, 5%, 0402

6.8 nH, 5%, 0402

L70

47 nH, 5%, 0402

12 nH, 5%, 0402

L71

47 nH, 5%, 0402

12 nH, 5%, 0402

Ω, 5%, 0402

Table 15. Component values for the matching network described in Figure 14 (DNM = Do

Not Mount).

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