CC1000-RTR2 datasheet(25/55 Pages) TI

25 / 55 page

CC1000

SWRS048A

Page 25 of 55

16. VCO

Only one external inductor (L101) is

required for the VCO. The inductor will

determine the operating frequency range

of the circuit. It is important to place the

inductor as close to the pins as possible in

order to reduce stray inductance. It is

recommended to use a high Q, low

tolerance inductor for best performance.

Typical tuning range for the integrated

varactor is 20-25%.

Component values for various frequencies

are given in Table 1. Component values

for other frequencies can be found using

the SmartRF

® Studio software.

17. VCO and PLL self-calibration

compensate

for

supply

voltage,

temperature and process variations the

VCO and PLL must be calibrated. The

calibration is done automatically and sets

maximum VCO tuning range and optimum

charge pump current for PLL stability.

After setting up the device at the operating

frequency, the self-calibration can be

initiated by setting the CAL_START bit.

The calibration result is stored internally in

the chip, and is valid as long as power is

not turned off. If large supply voltage

variations

(more

than

0.5

temperature variations (more than 40

degrees) occur after calibration, a new

calibration should be performed.

The self-calibration is controlled through

the

CAL

(see

configuration

registers

description

39).

The

CAL_COMPLETE bit indicates complete

calibration. The user can poll this bit, or

simply wait for 34 ms (calibration wait time

when CAL_WAIT = 1). The wait time is

proportional to the internal PLL reference

frequency. The lowest permitted reference

frequency (1 MHz) gives 34 ms wait time,

which is therefore the worst case.

Reference

frequency [MHz]

Calibration time

[ms]

2.4

2.0

1.5

1.0

The CAL_COMPLETE bit can also be

monitored at the CHP_OUT (LOCK) pin

(configured by LOCK_SELECT[3:0]) and

used

interrupt

input

the

microcontroller.

The CAL_START bit must be set to 0 by

the microcontroller after the calibration is

done.

There are separate calibration values for

the two frequency registers. If the two

frequencies, A and B, differ more than 1

MHz, or different VCO currents are used

(VCO_CURRENT[3:0] in the CURRENT

separately. When using a 10.7 MHz

external

the

10.7

MHz

below/above

the

transmit

frequency,

hence separate calibration must be done.

The CAL_DUAL bit in the CAL register

controls dual or separate calibration.

The single calibration algorithm, using

separate

calibration

for

and

frequency, is illustrated in Figure 16.

In Figure 17 the dual calibration algorithm

is shown for two RX frequencies. It could

also be used for two TX frequencies, or

even for one RX and one TX frequency if

the same VCO current is used.

In multi-channel and frequency hopping

applications the PLL calibration values

may be read and stored for later use. By

reading

back

calibration

values

and

frequency change can be done without

doing a re-calibration which could take up

to 34 ms. The calibration value is stored in

the TEST0 and TEST2 registers after a

calibration is completed. Note that when

using single calibration, calibration values

are

stored

separately

for

frequency

registers A and B. This means that the

TEST0 and TEST2 registers will contain

calibration

settings

for

the

currently

selected frequency register (selected by

F_REG

the

MAIN

The

calibration value can later be written into

TEST5

and

TEST

bypass

the

calibration.

Note

that

you

must

set

VCO_OVERRIDE=1

TEST5

and

CHP_OVERRIDE=1

the

TEST6

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