CC2500-RTR1 datasheet(49/84 Pages) TI

49 / 84 page

CC2500

PRELIMINARY Data Sheet (Rev.1.2)

SWRS040A

Page 49 of 83

30.2

Frequency

Hopping

and

Multi-

Channel Systems

The 2.400 – 2.4835 GHz band is shared by

many systems both in industrial, office and

home

environments.

therefore

recommended to use frequency hopping

spread spectrum (FHSS) or a multi-channel

protocol because the frequency diversity

makes the system more robust with respect to

interference from other systems operating in

the same frequency band. FHSS also combats

multipath fading.

CC2500 is highly suited for FHSS or multi-

channel systems due to its agile frequency

synthesizer

and

effective

communication

interface. Using the packet handling support

and data buffering is also beneficial in such

systems as these features will significantly

offload the host controller.

Charge pump current, VCO current and VCO

capacitance array calibration data is required

for

each

frequency

when

implementing

frequency hopping for

CC2500. There are 3

ways of obtaining the calibration data from the

chip:

1) Frequency hopping with calibration for each

hop. The PLL calibration time is approximately

720 µs.

2) Fast frequency hopping without calibration

for each hop can be done by calibrating each

frequency at startup and saving the resulting

FSCAL3

, FSCAL2 and FSCAL1 register values

in MCU memory. Between each frequency

hop, the calibration process can then be

replaced by writing the FSCAL3, FSCAL2 and

FSCAL1

next RF frequency. The PLL turn on time is

approximately 90 µs.

3) Run calibration on a single frequency at

startup. Next write 0 to FSCAL3[5:4] to

disable the charge pump calibration. After

writing to FSCAL3[5:4] strobe SRX (or STX)

with MCSM0.FS_AUTOCAL = 1 for each new

frequency hop. That is, VCO current and VCO

capacitance calibration is done but not charge

pump current calibration. When charge pump

current calibration is disabled the calibration

time is reduced from approximately 720 µs to

approximately 150 µs.

There is a trade off between blanking time and

memory space needed for storing calibration

data in non-volatile memory. Solution 2) above

gives the shortest blanking interval, but

requires more memory space to store

calibration

values.

Solution

gives

approximately 570 µs smaller blanking interval

than solution 1).

30.3

Wideband

Modulation

not

Using

Spread Spectrum

Digital modulation systems under FCC part

15.247 includes FSK and GFSK modulation.

A maximum peak output power of 1 W (+30

dBm) is allowed if the 6 dB bandwidth of the

modulated signal exceeds 500 kHz. In

addition, the peak power spectral density

conducted to the antenna shall not be greater

than +8 dBm in any 3 kHz band.

Operating at high data rates and high

frequency separation, the

CC2500 is suited for

systems targeting compliance with digital

modulation systems as defined by FCC part

15.247. An external power amplifier is needed

to increase the output above 0 dBm.

30.4

Data Burst Transmissions

The high maximum data rate of

CC2500 opens

up for burst transmissions. A low average data

rate link (e.g. 10 kbps), can be realized using a

higher over-the-air data rate. Buffering the

data and transmitting in bursts at high data

rate (e.g. 500 kbps) will reduce the time in

active mode, and hence also reduce the

average current consumption significantly.

Reducing the time in active mode will reduce

the likelihood of collisions with other systems,

e.g. WLAN.

30.5

Continuous Transmissions

In data streaming applications the

CC2500

opens up for continuous transmissions at 500

kbps effective data rate. As the modulation is

done with an I/Q up-converter with LO I/Q-

signals coming from a closed loop PLL, there

is no limitation in the length of a transmission.

(Open

loop

modulation

used

some

transceivers often prevents this kind of

continuous data streaming and reduces the

effective data rate.)

30.6

Crystal Drift Compensation

The

CC2500 has a very fine frequency

resolution (see Table 9). This feature can be

used to compensate for frequency offset and

drift.

The frequency offset between an ‘external’

transmitter and the receiver is measured in the

CC2500 and can be read back from the

CC2500-RTR1 数据表(PDF) 49 Page - Texas Instruments

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