MC3362 Datasheet, PDF (6/8 Pages) Motorola, Inc – LOW–POWER DUAL CONVERSION FM RECEIVER

MC3362
Following the first mixer, a 10.7 MHz ceramic band–pass
filter is recommended. The 10.7 MHz filtered signal is then
fed into one second mixer input pin, the other input pin being
connected to VCC. Pin 6 (VCC) is treated as a common point
for emitter–driven signals.
The 455 kHz IF is typically filtered using a ceramic
bandpass filter then fed into the limiter input pin. The limiter
has 10 µV sensitivity for – 3.0 dB limiting, flat to 1.0 MHz.
The output of the limiter is internally connected to the
quadrature detector, including a quadrature capacitor. A
parallel LC tank is needed externally from Pin 12 to VCC. A 39
kΩ shunt resistance is included which determines the peak
separation of the quadrature detector; a smaller value will
increase the spacing and linearity but decrease recovered
audio and sensitivity.
A data shaping circuit is available and can be coupled to
the recovered audio output of Pin 13. The circuit is a
comparator which is designed to detect zero crossings of
FSK modulation. Data rates are typically limited to 1200 baud
to ensure data integrity and avoid adjacent channel “splatter.”
Hysteresis is available by connecting a high valued resistor
from Pin 15 to Pin 14. Values below 120 kΩ are not
recommended as the input signal cannot overcome the
hysteresis.
The meter drive circuitry detects input signal level by
monitoring the limiting amplifier stages. Figure 4 shows the
unloaded current at Pin 10 versus input power. The meter
drive current can be used directly (RSSI) or can be used to
trip the carrier detect circuit at a specified input power. To do
this, pick an RF trip level in dBm. Read the corresponding
current from Figure 4 and pick a resistor such that:
' R10 0.64 Vdc / I10
Hysteresis is available by connecting a high valued resistor
RH between Pins 10 and 11. The formula is:
Hysteresis = VCC/(RH x 10 ^{– 7} ) dB
Figure 12. Circuit Side View
MC3362P
4I
REC. AUDIO
DATA
4I
METER
DRIVE
6
MOTOROLA ANALOG IC DEVICE DATA