RFW-D100 Vishay, RFW-D100 Datasheet - Page 30

• Manufacturer Part Number: RFW-D100
• Manufacturer: Vishay

Specifications of RFW-D100

• Operating Temperature (min): 0C
• Operating Temperature (max): 70C
• Operating Temperature Classification: Commercial
• Package Type: LQFP
• Operating Supply Voltage (min): 2.7V
• Operating Supply Voltage (typ): 3.3V
• Operating Supply Voltage (max): 3.6V
• Lead Free Status / Rohs Status: Supplier Unconfirmed

RFW-D100
Vishay RFWaves
APPENDIX A - RADIO SIGNAL STRENGTH
INDICATOR (RSSI)
General Description:
The RFW-D100 includes a special built-in Analog
module that supports Carrier detection. The principle
of operation is rather simple. In order to maintain a
‘well-behaved’ protocol under a CSMA assumption, It
would be highly efficient if each node could detect
whether “the air is free” or not. This would mean that
each node has the ability to find out prior to its own
transmission, whether or not some other pre-executed
transmissions are taking place simultaneously. Once
this “competitive transmission” has been detected, the
node just delays its own transmission until the current
transmission terminates. This carrier sense or “traffic
light” concept, reduces the probability of transmission
collisions within the primary network and moreover, it
avoids collisions that might occur with potential
At the back end, the peak detector power reference
voltage is being compared to a pre-defined reference
voltage. Once the detected power at the RFW
transceiver
pre-defined threshold (Slicers reference voltage) the
slicer comparator will change its output level from Low
to High, as an indication of “powerful” transmission
detection. Once the transmitted power level at the
receiver port will go 5 dB below the power threshold
(50 mV at the reference voltage), the slicer output will
resume its low level, thus indicating “free air” condition.
The following Figure is the complete RSSI block
diagram.
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30
occupied
Vout[Volts]
Vo
Bandwidth
noise floor level
Figure 11. The RFW122 Peak detector V
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reaches
the
intruder transmissions coming on from other networks
that share the same space.
Implementation:
The RFW transceiver RSSI module comprises two
main blocks. The front-end is a 20 MHz BW power
meter, centered at 2.44 GHz, while the back end is a
simple decision stage implemented as a voltage slicer.
The front-end power meter is designed to produce a
reference output voltage, which is correlated with the
detected radio power at the specified BW and
frequency. Figure 10 shows the power regulation of
the power meter. Note that the output voltage keeps
linearity over a wide range of input power (~ 75 dB)
with a characteristic slope of 10 mV/dB In order to
maintain the high dynamic range that is required, a
logarithmic peak detector is applied. It can be modeled
as V
V
out
out
is in volts (linear).
out
(PIN) Graph
=a*P
in
saturation
, where P
Pin[dBm]
in
is in dBm (logarithmic), and
Document Number 84675
Rev. 1.1, 22-Jan-07