CC2500 datasheet(24/76 Pages) TI

24 / 76 page

CC2500

Preliminary Data Sheet (rev.1.1.)

SWRS040

Page 24 of 77

12 Data Rate Programming

The data rate used when transmitting, or the

data rate expected in receive is programmed

the

MDMCFG3.DRATE_M

and

the

MDMCFG4.DRATE_E configuration registers.

The data rate is given by the formula below.

As the formula shows, the programmed data

rate depends on the crystal frequency.

()

XOSC

DRATE

DATA

DRATE

⋅

256

The following approach can be used to find

suitable values for a given data rate:

256

log

−

⋅

⎥

⎦

⎥

⎢

⎣

⎢

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

⋅

DRATE

XOSC

DATA

XOSC

DATA

DRATE

If DRATE_M is rounded to the nearest integer

and becomes 256, increment DRATE_E and

use DRATE_M=0.

The data rate can be set from 1.2 kbps to 500

kbps with the minimum step size of:

Data rate

start

Typical

data rate

Data rate

stop

Data rate

step size

0.8 kbps

1.2/2.4

kbps

3.17 kbps

0.0062 kbps

3.17 kbps

4.8 kbps

6.35 kbps

0.0124 kbps

6.35 kbps

9.6 kbps

12.7 kbps

0.0248 kbps

12.7 kbps

19.6 kbps

25.4 kbps

0.0496 kbps

25.4 kbps

38.4 kbps

50.8 kbps

0.0992 kbps

50.8 kbps

76.8 kbps

101.6 kbps

0.1984 kbps

101.6 kbps

153.6 kbps

203.1 kbps

0.3967 kbps

203.1 kbps

250 kbps

406.3 kbps

0.7935 kbps

406.3 kbps

500 kbps

1.5869 kbps

Table 19: Data rate step size

13 Receiver Channel Filter Bandwidth

In order to meet different channel width

requirements, the receiver channel filter is

programmable. The MDMCFG4.CHANBW_E and

MDMCFG4.CHANBW_M configuration registers

control the receiver channel filter bandwidth,

which scales with the crystal oscillator

frequency. The following formula gives the

relation between the register settings and the

channel filter bandwidth:

CHANBW

XOSC

channel

CHANBW

)·

(

⋅

The

CC2500 supports the following channel

filter bandwidths:

Table 20: Channel filter bandwidths [kHz]

(assuming a 26 MHz crystal)

Above 300 kHz bandwidth, however, the

sensitivity and blocking performance may be

somewhat degraded. For best performance,

the channel filter bandwidth should be

selected so that the signal bandwidth occupies

at most 80% of the channel filter bandwidth.

The channel centre tolerance due to crystal

accuracy should also be subtracted from the

signal bandwidth. The following example

illustrates this:

With the channel filter bandwidth set to 600

kHz, the signal should stay within 80% of 600

MDMCFG4.

MDMCFG4.CHANBW_E

CHANBW_M

812

406

203

102

650

325

162

541

270

135

464

232

116

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