MC3371 Datasheet, PDF (12/20 Pages) Motorola, Inc – LOW POWER FM IF

MC3371 MC3372
An external positive bias to Pin 12 sets up the squelch
trigger circuit such that the audio mute (Pin 14) is open or
connected to ground. If Pin 12 is pulled down to 0.9 V or
below by the noise or tone detector, Pin 14 is internally
shorted to ground. There is about 57 mV of hyteresis at
Pin 12 to prevent jitter. Audio muting is accomplished by
connecting Pin 14 to the appropriate point in the audio path
between Pin 9 and an audio amplifier. The voltage at Pin 14
should not be lower than –0.7 V; this can be assured by
connecting Pin 14 to the point that has no dc component.
Another possible application of the squelch switch may
be as a carrier level triggered squelch circuit, similar to the
MC3362/MC3363 FM receivers. In this case the meter
output can be used directly to trigger the squelch switch
when the RF input at the input frequency falls below the
desired level. The level at which this occurs is determined
by the resistor placed between the meter drive output
(Pin 13) and ground (Pin 15).
Figure 11. Typical Application for MC3371 at 10.7 MHz
VCC = 4.0 Vdc
RSSI Output
R2
10 k
+ _C9
10
1st IF 10.7 MHz
from Input
Front End
R3
100 k
8.2 µH
L2
C15
91
R11
560
C1
0.01
L1
TKANS9443HM
6.8 µH ±6%
R1
C17
51 k
0.1
16 15 14 13
Squelch Trigger
with Hysteresis
Mixer
Oscillator
1
2
3
4
C10
C2 ⁺ _R4
4.7
1.0 k
µF
D1 1N5817 _R5
4.7 k _R6
VR1 (Squelch Control)
10 k
C3
C4
560
0.1 0.001 _R7
R8
C5 ^{4.7 k}
0.001
3.3 k ^C7
0.022
C8
0.22
R9
510 k
VR2
10 k
12
11
10
9
Filter ^–
AF
Amp
Amp
+
Demodulator
Limiter
Amp
10
51 k 53 k
5 1.8 k 6
7
8
10.245
MHz
68 _C11
220
C12
C13
0.1
0.1 R10
39 k
AF Out
to Audio
Power Amp
T2: Toko
2A6597 HK (10 mm)
or
7MC–8128Z (7 mm)
muRata
C14
CFU455D2
0.1
or
equivalent
12
MOTOROLA ANALOG IC DEVICE DATA