MRF39RA Datasheet, PDF (16/72 Pages) Microchip Technology – Low-Power, Integrated UHF Receiver

MRF39RA
2.4.13
OPTIMIZING THE FLOOR
THRESHOLD
OokFixedThresh determines the sensitivity of the OOK
receiver as it sets the comparison threshold for weak
input signals (i.e., those close to the noise floor).
Significant sensitivity improvements can be generated
if configured correctly.
Note that the noise floor of the receiver at the
demodulator input depends on:
• The noise figure of the receiver
• The gain of the receive chain from antenna to
base band
• The matching, including SAW filter (if any)
• The bandwidth of the channel filters.
It is important to note that OokFixedThresh setting is
application-dependent. The following procedure as
illustrated in Figure 2-7 is recommended to optimize
OokFixedThresh.
FIGURE 2-7:
FLOOR THRESHOLD
OPTIMIZATION
Set MRF39RA in OOK Rx mode;
Adjust bit rate, channel filter BW
Default OokFixedThresh setting
No input signal
Continuous mode
Increment
OokFixedThresh
Monitor DIO2/DATA pin
Glitch activity
on DATA?
2.4.13.2 Alternative OOK Demodulator
Threshold Modes
In addition to the Peak OOK Threshold mode, the user
can alternatively select two other types of threshold
detectors:
• Fixed Threshold: the value is selected through
OokFixedThresh
• Average Threshold: data supplied by the RSSI
block is averaged and this operation mode must
be used only with DC-free encoded data.
2.4.14 BIT SYNCHRONIZER
The bit synchronizer is a block that provides a clean
and synchronized digital output, free of glitches. Its
output is made available on pin DIO1/DCLK in
Continuous mode and can be disabled through register
settings. However, for optimum receiver performance it
is used when running Continuous mode is strongly
advised.
The bit synchronizer is automatically activated in
Packet mode. Its bit rate is controlled by BitRateMsb
and BitRateLsb in RegBitrate.
Optimization complete
The new floor threshold value found during this test
must be used for OOK reception with those receiver
settings.
2.4.13.1 Optimizing OOK Demodulator for
Fast Fading Signals
A sudden drop in signal strength can cause the bit error
rate to increase. For applications where the expected
signal drop can be estimated, the OokPeakThreshStep
and OokPeakThreshDec parameters can be optimized
for a given number of threshold decrements per bit.
Refer to RegOokPeak to access those settings.
DS40001778B-page 16
 2015 Microchip Technology Inc.