AN1833 Freescale Semiconductor / Motorola, AN1833 Datasheet - Page 16

• Manufacturer Part Number: AN1833
• Description: A Low-Power Wireless Remote Control Transmitter and Receiver
• Manufacturer: Freescale Semiconductor / Motorola

Application Note
Data Recovery
Circuit
16
The received OOK signal is converted from RF to baseband by the
MC13158 RSSI function. The RSSI output sources a current to an
external load connected to V
load resistance affects the receiver performance. Obviously, the
resulting RSSI gain (V
When this load is large enough, the RSSI output will saturate, which will
compress the high RF input end of the RSSI transfer response. A load
of 100 k is a good choice to obtain 70 dB of monotonic RSSI dynamic
range with no compression. The load impedance chosen also affects the
RSSI rise and fall times (see
times are more than adequate to follow signal amplitude variations to
rates greater than 50 kHz.
For data rates of 10 kHz or less, 680 pF and 100 k may be connected
from pin 24 to V
corner at approximately 10 kHz; this helps clean up the RSSI response
under low signal conditions. Data rates up to 50 kHz have been achieved
without low pass filtering.
The RSSI is dc coupled to the data slicer non-inverting input (pin 20).
The data slicer inverting input terminal is referenced to V
voltage divider or a diode to ground. Temperature stability of this
reference should be considered for receiver operating over an extended
temperature range.
The data slicer can be disabled by connecting the data slicer off pin to
greater than 1.5 Vdc (V
integrated with a transmitter, this will prevent an invalid data slicer output
from causing problems.
Freescale Semiconductor, Inc.
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. These components form a low pass filter with its
Out
CC
/RF
will suffice). Should the receiver system be
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In
Figure
) is directly proportionate to this load.
to produce a voltage. The choice of this
5). The RSSI output rise and fall
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with a
MOTOROLA
AN1833