CC2500RGPR Datasheet, PDF (17/99 Pages) Texas Instruments – Low-Cost Low-Power 2.4 GHz RF Transceiver

6 Circuit Description
RADIO CONTROL
LNA
RF_P
RF_N
ADC
ADC
0
FREQ
90
SYNTH
PA
CC2500
SCLK
SO (GDO1)
SI
CSn
GDO0 (ATEST)
GDO2
RC OSC
BIAS
XOSC
RBIAS XOSC_Q1 XOSC_Q2
Figure 2: CC2500 Simplified Block Diagram
A simplified block diagram of CC2500 is shown
in Figure 2.
CC2500 features a low-IF receiver. The
received RF signal is amplified by the low-
noise amplifier (LNA) and down-converted in
quadrature (I and Q) to the intermediate
frequency (IF). At IF, the I/Q signals are
digitised by the ADCs. Automatic gain control
(AGC), fine channel filtering, demodulation
bit/packet synchronization are performed
digitally.
The transmitter part of CC2500 is based on
direct synthesis of the RF frequency.
The frequency synthesizer includes a
completely on-chip LC VCO and a 90 degrees
phase shifter for generating the I and Q LO
signals to the down-conversion mixers in
receive mode.
A crystal is to be connected to XOSC_Q1 and
XOSC_Q2. The crystal oscillator generates the
reference frequency for the synthesizer, as
well as clocks for the ADC and the digital part.
A 4-wire SPI serial interface is used for
configuration and data buffer access.
The digital baseband includes support for
channel configuration, packet handling, and
data buffering.
7 Application Circuit
Only a few external components are required
for using the CC2500. The recommended
application circuit is shown in Figure 3. The
external components are described in Table
14, and typical values are given in Table 15.
Bias Resistor
The bias resistor R171 is used to set an
accurate bias current.
Balun and RF Matching
The components between the RF_N/RF_P pins
and the point where the two signals are joined
together (C122, C132, L121, and L131) form a
SWRS040C
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