AN1833 Freescale Semiconductor / Motorola, AN1833 Datasheet - Page 4

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

Freescale Semiconductor, Inc.
Application Note
parasitic feedback between the output and input of the high gain RF
amplifier chain creates oscillation at the center frequency. Reducing the
gain in the RF amplifier chain may prevent oscillations but lower gain will
reduce the sensitivity of the receiver. These receivers generally use
discrete semiconductors since integrated circuits are not available for
low-voltage, low-power applications.
The more reliable and stable receiver described in this application note
is a superheterodyne type receiver. In this receiver, the RF carrier is
filtered and amplified using an RF preamplifier and is down converted
using a mixer and local oscillator (LO) to a convenient, lower frequency
called the intermediate frequency (IF). The IF signal is amplified and
filtered and then demodulated by using an appropriate detector.
The OOK receiver shown in
Figure 1a
has many advantages over a
TRF receiver. It utilizes two monolithic integrated circuits (IC), the
MC13144 [2] as a cascade low-noise amplifier (LNA), and the
MC13158 [3] as the main building block components of the receiver.
This receiver offers very stable operation with more than 115 dB of
stable gain. Typical sensitivity is –100 dBm which allows for a greater
operating distance between transmitter and receiver. By utilizing a
varactor-controlled LO locked by an external automatic frequency
control (AFC) circuit, the receiver has the ability to lock onto the
transmitter. Thus, this receiver system has no need to use a more
expensive crystal oscillator for the LO.
The OOK transmitter
(Figure
1b) is implemented by using a versatile
1-chip, fixed frequency PLL (phase-locked loop) system IC, the
MC13176D [4] which operates under an inexpensive crystal reference
source from a microcontroller unit, the MC68HC705J1A [5].
Baseband processing functions are performed by MCUs in both the
remote receiver and handheld transmitter.
AN1833
4
MOTOROLA
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