CC1070-RTY1 datasheet(38/57 Pages) TI2

38 / 57 page

CC1070

SWRS043A

Page 38 of 54

to Application Note AN027 Temperature

Compensation available from the TI web

site.

In less demanding applications, a crystal

with low temperature drift and low aging

could

used

without

further

compensation. A trimmer capacitor in the

crystal oscillator circuit (in parallel with C5)

could be used to set the initial frequency

accurately.

CC1070 also has the possibility to use

Gaussian shaped FSK (GFSK). This

spectrum-shaping

feature

improves

adjacent

channel

power

(ACP)

and

occupied bandwidth. In ‘true’ FSK systems

with

abrupt

frequency

shifting,

the

spectrum is inherently broad. By making

the frequency shift ‘softer’, the spectrum

can be made significantly narrower. Thus,

higher data rates can be transmitted in the

same bandwidth using GFSK.

Low cost systems

As the

CC1070 provide true narrowband

multi-channel performance without any

external filters, a very low cost high

performance system can be achieved.

The oscillator crystal can then be a low

cost crystal with 50 ppm frequency

tolerance using the on-chip frequency

tuning possibilities.

Battery operated systems

In low power applications the power down

mode should be used when

CC1070 is not

being active. Depending on the start-up

time requirement the oscillator core can be

powered during power down. See section

16 on page 33 for information on how

effective power management can be

implemented.

Frequency hopping spread spectrum

systems (FHSS)

Due to the very fast locking properties of

the PLL, the

CC1070 is also very suitable

for frequency hopping systems. Hop rates

of 1-100 hops/s are commonly used

depending on the bit rate and the amount

data

sent

during

each

transmission. The two frequency registers

(FREQ_A and FREQ_B) are designed

such that the ‘next’ frequency can be

programmed while the ‘present’ frequency

is used. The switching between the two

frequencies is performed through use of

the MAIN register. For more details refer

to Application Note AN014 Frequency

Hopping Systems available from the TI

web site.

In order to implement a frequency hopping

system with

CC1070 do the following:

Set the desired frequency, calibrate and

store the following register settings in non-

volatile memory:

STATUS1[3:0]: CHP_CURRENT[3:0]

STATUS2[4:0]: VCO_ARRAY[4:0]

STATUS3[5:0]:VCO_CAL_CURRENT[5:0]

Repeat the calibration for each desired

frequency. VCO_CAL_CURRENT[5:0] is

not dependent on the RF frequency and

the same value can be used for all

frequencies.

When performing frequency hopping, write

the stored values to the corresponding

TEST1, TEST2 and TEST3 registers, and

enable override:

TEST1[3:0]: CHP_CO[3:0]

TEST2[4:0]: VCO_AO[4:0]

TEST2[5]: VCO_OVERRIDE

TEST2[6]: CHP_OVERRIDE

TEST3[5:0]: VCO_CO[5:0]

TEST3[6]: VCO_CAL_OVERRIDE

CHP_CO[3:0] is the register setting read

from CHP_CURRENT[3:0], VCO_AO[4:0]

the register setting read from

VCO_ARRAY[4:0] and VCO_CO[5:0] is

the

setting

read

from

VCO_CAL_CURRENT[5:0].

Assume channel 1 defined by register

FREQ_A is currently being used and that

CC1070 should operate on channel 2 next

(to change channel simply write to register

MAIN[6]). The channel 2 frequency can be

set by register FREQ_B which can be

written to while operating on channel 1.

The calibration data must be written to the

TEST1-3 registers after switching to the

next frequency. That is, when hopping to a

new channel write to register MAIN[6] first

and the test registers next. The PA should

be switched off between each hop and the

PLL should be checked for lock before

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