MC3356_1 Datasheet, PDF (4/8 Pages) Motorola, Inc – Wideband FSK Receiver

Freescale Se_Mm_C3i₃c₅o₆nductor, Inc.
Figure 5. Application with Fixed Bias on Data Shaper
RF In
1:2
0.01
Data Out
5.0 V
18 k
Car. Det. Out
0 V or 4.0 V _{3.3 k}
130 k
15 k
10 k
10 k
390 k
3.0 k
0.1 470
pF
18 k
3.3 k
20
19
RF Input Ground
18
Data
Output
17
Comp(+)
16
15
Comp(–) Squelch
Status
14
13
Squelch Demod
Control Out
12
Demod
Filter
11
Quad
Input
MC3356
150 pF
RF
OSC
OSC RF
Mixer
Limiter Limiter Limiter Quad
Gnd
EM.
COL. VCC
Out
VCC
Input
Bias Bias
Bias
1
2
3
4
5
6
7
8
9
10
5.0 V
15 pF
5.6 pF fO
0.01
+ 5.0 to + 12 V
0.01
Bead
4.0 V
330
0.1
Cer. Fil.
10.7 MHz
330
0.01
0.01
0.01
Bead
0.1
180
82
APPLICATION NOTES (continued)
Shielding, which includes the placement of input and
output components, is important in minimizing electrostatic or
electromagnetic coupling. The MC3356 has its pin
connections such that the circuit designer can place the
critical input and output circuits on opposite ends of the chip.
Shielding is normally required for inductors in tuned circuits.
The MC3356 has a separate VCC and ground for the RF
and IF sections which allows good external circuit isolation by
minimizing common ground paths.
Note that the circuits of Figures 1 and 2 have RF,
Oscillator, and IF circuits predominantly referenced to the
plus supply rails. Figure 5, on the other hand, shows a
suitable means of ground referencing. The two methods
produce identical results when carefully executed. It is
important to treat Pin 19 as a ground node for either
approach. The RF input should be ‘‘grounded’’ to Pin 1 and
then the input and the mixer/oscillator grounds (or RF VCC
bypasses) should be connected by a low inductance path to
Pin 19. IF and detector sections should also have their
bypasses returned by a separate path to Pin 19. VCC and
RF VCC can be decoupled to minimize feedback, although
the configuration of Figure 2 shows a successful
implementation on a common 5.0 V supply. Once again, the
message is: define a supply node and a ground node and
return each section to those nodes by separate, low
impedance paths.
The test circuit of Figure 2 has a 3 dB limiting level of
30 µV which can be lowered 6 db by a 1:2 untuned
transformer at the input as shown in Figures 5 and 6. For
applications that require additional sensitivity, an RF amplifier
can be added, but with no greater than 20 db gain. This will
give a 2.0 to 2.5 µV sensitivity and any additional gain will
reduce receiver dynamic range without improving its
sensitivity. Although the test circuit operates at 5.0 V, the
mixer/oscillator optimum performance is at 8.0 V to 12 V. A
minimum of 8.0 V is recommended in high frequency
applications (above 150 MHz), or in PLL applications where
the oscillator drives a prescaler.
4
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