CC1020-RTR1 datasheet(63/91 Pages) TI

63 / 91 page

CC1020

SWRS046

Page 63 of 92

system. Even initial adjustment can be

performed

using

the

frequency

programmability. This eliminates the need

for an expensive TCXO and trimming in

some applications. For more details refer

to Application Note AN027 Temperature

Compensation available from the Chipcon

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.

The

frequency

offset

between

transmitter and receiver is measured in the

CC1020 and can be read back from the

AFC register. The measured frequency

offset can be used to calibrate the receiver

frequency using the transmitter as the

reference. For more details refer to

Application Note AN029 CC1020/1021

AFC available from the Chipcon web site.

CC1020 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

CC1020 provides 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

CC1020 is not

being active. Depending on the start-up

time requirement, the oscillator core can

be powered during power down. See

section 17 on page 54 for information on

how effective power management can be

implemented.

High reliability systems

Using a SAW filter as a preselector will

improve the communication reliability in

harsh environments by reducing the

probability of blocking. The receiver

sensitivity and the output power will be

reduced due to the filter insertion loss. By

inserting the filter in the RX path only,

together with an external RX/TX switch,

only the receiver sensitivity is reduced and

output power is remained. The PA_EN

and LNA_EN pin can be configured to

control an external LNA, RX/TX switch or

power amplifier. This is controlled by the

INTERFACE register.

Frequency hopping spread spectrum

systems (FHSS)

Due to the very fast locking properties of

the PLL, the

CC1020 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 done through the MAIN

included to do the hopping without a need

to re-synchronize the receiver. For more

details refer to Application Note AN014

Frequency Hopping Systems available

from the Chipcon web site.

In order to implement a frequency hopping

system with

CC1020 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:

CC1020-RTR1 Datenblatt(PDF) 63 Page - Texas Instruments

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