MC3356 Motorola, MC3356 Datasheet - Page 5

• Manufacturer Part Number: MC3356
• Description: GENERAL PURPOSE TRANSISTOR ARRAY
• Manufacturer: Motorola

APPLICATION NOTES (continued)
noninverted data is available at Pin 18. Inverted data makes
the higher frequency in the FSK signal a “one” when the local
oscillator is above the incoming RF. Figure 5 schematic
shows the comparator with hysteresis. In this circuit the dc
reference voltage at Pin 17 is about the same as the
demodulated output voltage (Pin 13) when no signal is
present. This type circuit is preferred for systems where the
data rates can drop to zero. Some systems have a low
frequency limit on the data rate, such as systems using the
MC3850 ACIA that has a start or stop bit. This defines the
low frequency limit that can appear in the data stream.
MOTOROLA ANALOG IC DEVICE DATA
RF In
Depending on
1:2
0.01
RF Input
the
20
external
Ground
Figure 6. Application with Self–Adjusting Bias on Data Shaper
Data
Out
19
Output
Data
5.0 V
circuit,
18
1
10 k
470 k
Comp(+) Comp(–) Squelch
17
470 pF
inverted
47 k
16
0.1
47 k
Car. Det. Out
MC3356
or
Status
15
0 V or 4.0 V
130 k
3.3 k
Squelch
Figure 5 circuit can then be changed to a circuit configuration
as shown in Figure 6. In Figure 6 the reference voltage for
the comparator is derived from the demodulator output
through a low pass circuit where
lowest frequency data rate. This and similar circuits will
compensate for small tuning changes (or drift) in the
quadrature detector.
input signal becomes greater than some preset level set by
the resistance between Pin 14 and ground. Hysteresis is
added to the circuit externally by the resistance from Pin 14 to
Pin 15.
Control
14
3.3 k
0.1
Squelch status (Pin 15) goes high (squelch off) when the
Demod
Out
13
470
pF
Demod
Filter
12
15 k
18 k
Quad
Input
11
f = 10.7
150 pF
is much lower than the
1.5 H
5