CC2500-RTR1 datasheet(56/96 Pages) TI

56 / 96 page

CC2500

SWRS040C

Page 56 of 89

31.6

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

FREQEST

status register as described in

Section 14.1. The measured frequency offset

can be used to calibrate the frequency using

the ‘external’ transmitter as the reference. That

is, the received signal of the device will match

the receiver’s channel filter better. In the same

way the centre frequency of the transmitted

signal will match the ‘external’ transmitter’s

signal.

31.7

Spectrum Efficient Modulation

CC2500 also has the possibility to use

Gaussian

shaped

2-FSK

(GFSK).

This

spectrum-shaping feature improves adjacent

channel

power

(ACP)

and

occupied

bandwidth. In ‘true’ 2-FSK systems with abrupt

frequency shifting, the spectrum is inherently

broad. By making the frequency shift ‘softer’,

the

spectrum

can

made

significantly

narrower. Thus, higher data rates can be

transmitted in the same bandwidth using

GFSK.

31.8

Low Cost Systems

A differential antenna will eliminate the need

for a balun, and the DC biasing can be

achieved in the antenna topology, see Figure

3. The CC25XX Folded Dipole reference

design [8] contains schematics and layout files

for a CC2500EM with a folded dipole PCB

antenna. Please see DN004 [9] for more

details on this design.

A HC-49 type SMD crystal is used in the

CC2500EM reference design [4]. Note that the

crystal package strongly influences the price.

In a size constrained PCB design a smaller,

but more expensive, crystal may be used.

31.9

Battery Operated Systems

In low power applications, the SLEEP state

with the crystal oscillator core switched off

should be used when the

CC2500 is not active.

It is possible to leave the crystal oscillator core

running in the SLEEP state if start-up time is

critical.

The WOR functionality should be used in low

power applications.

31.10

Increasing Output Power

In some applications it may be necessary to

extend the link range. Adding an external

power amplifier is the most effective way of

doing this.

The

power

amplifier

should

inserted

between the antenna and the balun, and two

T/R switches are needed to disconnect the PA

in RX mode. See Figure 29.

Figure 29. Block Diagram of

CC2500 Usage with External Power Amplifier

CC2500

Balun

Filter

Antenna

T/R switch

CC2500-RTR1 数据表(PDF) 56 Page - Texas Instruments

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