mc3371dtb ETC-unknow, mc3371dtb Datasheet - Page 11

• Manufacturer Part Number: mc3371dtb
• Description: Low Power Narrowband Fm If
• Manufacturer: ETC-unknow

receivers with an operating frequency of up to 60 MHz. Its low
voltage design provides low power drain, excellent
sensitivity, and good image rejection in narrowband voice
and data link applications.
limiter with a logarithmic response signal strength indicator, a
quadrature detector, an active filter and a squelch trigger
circuit. In a typical application, the mixer amplifier converts an
RF input signal to a 455 kHz IF signal. Passing through an
external bandpass filter, the IF signal is fed into a limiting
amplifier and detection circuit where the audio signal is
recovered. A conventional quadrature detector is used.
presence of noise above the desired audio frequencies. This
“noise band” is monitored by an active filter and a detector. A
squelch switch is used to mute the audio when noise or a
tone is present. The input signal level is monitored by a meter
drive circuit which detects the amount of IF signal in the
limiting amplifier.
collector, base, and emitter connections at Pins 4, 1 and 2
respectively. This oscillator can be run under crystal control.
For fundamental mode crystals use crystal characterized
parallel resonant for 32 pF load. For higher frequencies, use
3rd overtone series mode type crystals. The coil (L2) and
resistor RD (R13) are needed to ensure proper and stable
operation at the LO frequency (see Figure 13, 45 MHz
application circuit).
Conversion gain stated in the AC Electrical Characteristics
table is typically 20 dB. This power gain measurement was
made under stable conditions using a 50
input and an external load provided by a 455 kHz ceramic
filter at the mixer output which is connected to the V CC (Pin 4)
and IF input (Pin 5). The filter impedance closely matches the
1.8 k internal load resistance at Pin 3 (mixer output). Since
the input impedance at Pin 16 is strongly influenced by a
3.3 k
the useful gain is actually much higher than shown by the
standard power gain measurement. The Smith Chart plot in
Figure 17 shows the measured mixer input impedance
versus input frequency with the mixer input matched to a
50
assure stable operation under matched conditions, it is
necessary to provide a shunt resistor to ground. Figures 11,
12 and 13 show the input networks used to derive the mixer
input impedance data.
recommended for IF filtering (i.e. 455 kHz types having a
bandwidth of 2.0 kHz to 15 kHz with an input and output
impedance from 1.5 k
MOTOROLA ANALOG IC DEVICE DATA
The MC3371 and MC3372 are low power narrowband FM
This part combines a mixer, an IF (intermediate frequency)
The absence of an input signal is indicated by the
The oscillator is an internally biased Colpitts type with the
The mixer is doubly balanced to reduce spurious radiation.
Following the mixer, a ceramic bandpass filter is
source impedance at the given frequencies. In order to
internal biasing resistor and has a low capacitance,
APPLICATIONS INFORMATION
CIRCUIT DESCRIPTION
to 2.0 k ). The 6 stage limiting IF
source at the
MC3371 MC3372
amplifier has approximately 92 dB of gain. The MC3371 and
MC3372 are different in the limiter and quadrature detector
circuits. The MC3371 has a 1.8 k
providing internal dc biasing and the output of the limiter is
internally connected, both directly and through a 10 pF
capacitor to the quadrature detector; whereas, in the
MC3372 these components are not provided internally. Thus,
in the MC3371, no external components are necessary to
match the 455 kHz ceramic filter, while in the MC3372,
external 1.8 k
between Pins 5 and 7, respectively (see Figures 12 and 13).
connected externally from Pin 8 to V CC (similar to the
MC3361). In the MC3372, a quadrature capacitor is needed
externally from Pin 7 to Pin 8 and a parallel LC or a ceramic
discriminator with a damping resistor is also needed from
Pin 8 to V CC (similar to the MC3357). The above external
quadrature circuitry provides 90 phase shift at the IF center
frequency and enables recovered audio.
the detector and is somewhat critical. As the resistor is
decreased, the separation and the bandwidth is increased
but the recovered audio is decreased. Receiver sensitivity is
dependent on the value of this resistor and the bandwidth of
the 455 kHz ceramic filter.
carrier component and modulating signal, is passed through
a low pass filter amplifier to reduce the carrier component
and then is fed to Pin 9 which has an output impedance of
450
the carrier component, deemphasis, volume control, and
further amplification before driving a loudspeaker. The
relative level of the composite recovered audio signal at Pin 9
should be considered for proper interaction with an audio
post amplifier and a given load element. The MC13060 is
recommended as a low power audio amplifier.
the output current is proportional to the logarithm of the IF
input signal amplitude. A maximum source current of 60 A is
available and can be used to drive a meter and to detect a
carrier presence. This is referred to as a Received Strength
Signal Indicator (RSSI). The output at Pin 13 provides a
current source. Thus, a resistor to ground yields a voltage
proportional to the input carrier signal level. The value of this
resistor is estimated by (V CC (Vdc) – 1.0 V)/60 A; so for
V CC = 4.0 Vdc, the resistor is approximately 50 k
provides a maximum voltage swing of about 3.0 V.
inverting input at Pin 10. The noninverting input is connected
to 2.5 V. The op amp may be used as a noise triggered
squelch or as an active noise filter. The bandpass filter is
designed with external impedance elements to discriminate
between frequencies. With an external AM detector, the
filtered audio signal is checked for a tone signal or for the
presence of noise above the normal audio band. This
information is applied to Pin 12.
In the MC3371, a parallel LCR quadrature tank circuit is
The damping resistor determines the peak separation of
On the chip the composite recovered audio, consisting of
The meter output indicates the strength of the IF level and
A simple inverting op amp has an output at Pin 11 and the
. The signal still requires further filtering to eliminate
and 51 k
biasing resistors are needed
and a 51 k
resistor
11
and