CC2480_11 Datasheet, PDF (33/48 Pages) Texas Instruments – Z-Accel 2.4 GHz ZigBee Processor

CC2480
10.7 Linear IF and AGC Settings
CC2480 is based on a linear IF chain where the
signal amplification is done in an analog VGA
(variable gain amplifier). The gain of the VGA
is digitally controlled.
10.8 Clear Channel Assessment
The clear channel assessment signal is based
on the measured RSSI value and a
programmable threshold. The clear channel
assessment function is used to implement the
10.9 VCO and PLL Self-Calibration
10.9.1 VCO
The VCO is completely integrated and
operates at 4800 – 4966 MHz. The VCO
frequency is divided by 2 to generate
10.9.2 PLL self-calibration
The VCO's characteristics will vary with
temperature, changes in supply voltages, and
the desired operating frequency.
10.10 Input / Output Matching
The RF input / output is differential (RF_N and
RF_P). In addition there is supply switch output
pin (TXRX_SWITCH) that must have an
external DC path to RF_N and RF_P.
In RX mode the TXRX_SWITCH pin is at
ground and will bias the LNA. In TX mode the
TXRX_SWITCH pin is at supply rail voltage and
will properly bias the internal PA.
The AGC (Automatic Gain Control) loop
ensures that the ADC operates inside its
dynamic range by using an analog/digital
feedback loop.
CSMA-CA functionality specified in [1]. CCA is
valid when the receiver has been enabled for
at least 8 symbol periods.
frequencies in the desired band (2400-2483.5
MHz).
In order to ensure reliable operation the VCO’s
bias current and tuning range are
automatically calibrated every time the RX
mode or TX mode is enabled.
The RF output and DC bias can be done using
different topologies. Some are shown in Figure
5 on page 21.
Component values are given in Table 19 on
page 22. If a differential antenna is
implemented, no balun is required.
If a single ended output is required (for a
single ended connector or a single ended
antenna), a balun should be used for optimum
performance.
CC2480 Data Sheet SWRS074
Page 33 of 43