AN1833 Freescale Semiconductor / Motorola, AN1833 Datasheet - Page 8

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

Application Note
8
NOTE:
The IF chain is split into two sections to allow IF bandpass filtering in two
places:
Output impedance driving each filter port is 330 , which is ideal for
common ceramic IF filters centered at 10.7 MHz. The IF and limiter
amplifier’s internal inputs are 330
ceramic filters.
The limiter is coupled internally to the quadrature detector inputs, and it
is also pinned out. An external RLC (resistance-inductance-
capacitance) tank provides selection of the demodulator tuned
frequency and detection bandwidth. The detected signal is brought out
by the inverting amplifier buffer. Its output amplitude swing is set by an
external feedback resistor from the output (pin 17) to the input of the
inverting amplifier (pin 15). It is combined with a second resistor from the
input to the negative supply (pin 16) to select the output dc level.
The RSSI (received signal strength indicator) output provides an output
current that is proportionate to the logarithm of the receiver input voltage.
Externally load it with a resistor to V
Its typical transfer gain is 0.4 A per dB of input drive level. The RSSI
dynamic range is higher than 70 dB, which is achieved by sensing signal
strength at each stage of the IF and limiter amplifiers and summing them
together. The RSSI linearity is affected by the loss placed between the
IF amplifier and the limiter amplifier; a total midband attenuation of 10 dB
is optimal.
The data slicer comparator has more than 500 kHz of toggling capability.
Its inverting input (pin 18) and non-inverting input (pin 20) have
back-to-back diodes across them. The recovered signal may be dc
coupled to one data slicer input while the other one is ac grounded; it is
allowed to swing 1 V
The polarity of the output data depends on which input is referenced to
V
non-inverting input. Where the reference input pin of the data slicer is
EE
1. Between the mixer and IF amplifier
2. Between the IF and limiter amplifiers
Freescale Semiconductor, Inc.
(ground). For positive logic data output, the data signal goes to the
For More Information On This Product,
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BE
about the dc level to the comparator input.
EE
to ground to match the 10.7-MHz
.
MOTOROLA
AN1833