MC3363
parallel LC tank is needed externally from Pin 14 to V . A 68
kΩ shunt resistance is included which determines the peak
separation of the quadrature detector; a smaller value will
lower the Q and expand the deviation range 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 16. The circuit is a
comparator which is designed to detect zero crossings of
FSK modulation. Data rates of up to 35000 baud are
detectable using the comparator. Best sensitivity is obtained
when data rates are limited to 1200 baud maximum.
Hysteresis is available by connecting a high-valued resistor
from Pin 17 to Pin 18. Values below 120 kΩ are not
recommended as the input signal cannot overcome the
hysteresis.
CIRCUIT DESCRIPTION
CC
The MC3363 is a complete FM narrowband receiver from
RF amplifier to audio preamp output. The low voltage dual
conversion design yields low power drain, excellent
sensitivity and good image rejection in narrowband voice and
data link applications.
In the typical application, the input RF signal is amplified
by the RF transistor and then the first mixer amplifies the
signal and converts the RF input to 10.7 MHz. This IF signal
is filtered externally and fed into the second mixer, which
further amplifies the signal and converts it to a 455 kHz IF
signal. After external bandpass filtering, the low IF is fed into
the limiting amplifier and detection circuitry. The audio is
recovered using a conventional quadrature detector.
Twice-IF filtering is provided internally.
The meter drive circuitry detects input signal level by
monitoring the limiting of the limiting amplifier stages.
Figure 5 shows the unloaded current at Pin 12 versus input
power. The meter drive current can used directly (RSSI) or
can be used to trip the carrier detect circuit at a specified
input power.
The input signal level is monitored by meter drive circuitry
which detects the amount of limiting in the limiting amplifier.
The voltage at the meter drive pin determines the state of the
carrier detect output, which is active low.
APPLICATIONS INFORMATION
A muting op amp is provided and can be triggered by the
carrier detect output (Pin 13). This provides a carrier level
triggered squelch circuit which is activated when the RF input
at the desired input frequency falls below a present level. The
level at which this occurs is determined by the resistor placed
The first local oscillator is designed to serve as the VCO in
a PLL frequency synthesized receiver. The MC3363 can
operate together with the MC145166/7 to provide a two-chip
ten–channel frequency synthesized receiver in the 46/49
cordless telephone band. The MC3363 can also be used with
the MC14515X series of CMOS PLL synthesizers and
MC120XX series of ECL prescalers in VHF frequency
synthesized applications to 200 MHz.
between the meter drive output (Pin 12) and V . Values
CC
between 80–130 kΩ are recommended. This type of squelch
is pictured in Figures 3 and 4.
Hysteresis is available by connecting a high-valued
resistor Rh between Pins 12 and 13. The formula is:
For single channel applications the first local oscillator can
be crystal controlled. The circuit of Figure 4 has been used
successfully up to 60 MHz. For higher frequencies an
external oscillator signal can be injected into Pins 25 and/or
26 — a level of approximately 100 mVrms is recommended.
The first mixer′s transfer characteristic is essentially flat to
450 MHz when this approach is used (keeping a constant
10.7 MHz IF frequency). The second local oscillator is a
Colpitts type which is typically run at 10.245 MHz under
crystal control.
The mixers are doubly balanced to reduce spurious
responses. The first and second mixers have conversion
gains of 18 dB and 21 dB (typical), respectively. Mixer gain is
stable with respect to supply voltage. For both conversions,
the mixer impedances and pin layout are designed to allow
the user to employ low cost, readily available ceramic filters.
Following the first mixer, a 10.7 MHz ceramic bandpass
filter is recommended. The 10.7 MHz filtered signal is then
fed into the second mixer input Pin 21, the other input Pin 22
–7
/ (Rh x 10 ) dB
Hyst = V
CC
The meter drive can also be used directly to drive a meter
or to provide AGC. A current to voltage converter or other
linear buffer will be needed for this application.
A second possible application of the op amp would be in a
noise triggered squelch circuit, similar to that used with the
MC3357/MC3359/MC3361B FM IFs. In this case the op amp
would serve as an active noise filter, the output of which
would be rectified and compared to a reference on a squelch
gate. The MC3363 does not have a dedicated squelch gate,
but the NPN RF input stage or data shaping comparator
might be used to provide this function if available. The op
amp is a basic type with the inverting input and the output
available. This application frees the meter drive to allow it to
be used as a linear signal strength monitor.
The circuit of Figure 4 is a complete 50 MHz receiver from
antenna input to audio preamp output. It uses few
components and has good performance. The receiver
operates on a single channel and has input sensitivity of
0.3 µV for 12 dB SINAD.
being connected to V
.
CC
The 455 kHz IF is filtered by a ceramic narrow bandpass
filter then fed into the limiter input Pin 9. 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
NOTE: For further application and design information, refer to AN980.
4
MOTOROLA ANALOG IC DEVICE DATA
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