External Components and Interfacing
V
DD
C
9
V
SS
XTAL
1
X
1
24
23
22
21
20
CHIP SELECT
SERIAL DATA INPUT
SERIAL CLOCK INPUT
SQUELCH DRIVE
NOISE OUTPUT
R
2
2
V
DD
XTAL/CLOCK
POST PROCESS
AUDIO INPUT
C
7
3
4
PRE-PROCESS AUDIO OUTPUT
Rx
AUDIO INPUT
C
6
V
BIAS
CTCSS/DATA INPUT
Tx AUDIO INPUT
5
6
7
8
9
C
FX506P
R
4
NOISE INPUT
R.S.S.I.
VCO DRIVE (Tx)
VCO REF. DRIVE (Tx)
19
18
17
16
15
14
13
V
SS
SEE
FIG.3
BELOW
MIC. OUTPUT
MIC. INPUT 1
MIC. INPUT 2
3
10
11
12
C
AUDIO OUTPUT (Rx)
COMPRESSION
CAPACITOR
5
R
3
C
2
C
C
4
1
C
8
R
V
SS
1
V
BIAS
Fig.2 Recommended External Components
Notes
MIC. I/P
1
R
6
10
C
10
11
C
3
/C
4
12
MIC. O/P
–
R
5
Tx
AUDIO INPUT
9
MIC. I/P
2
BIAS
+
EXTERNAL
OP-AMP
Fig.3 Typical 2nd Order Pre-emphasis Input Circuit
For dual Tx inputs using both Mic.1 and Mic.2 inputs without
pre-emphasis, capacitors C
3
and C
4
will be required at the
inputs as shown in Figure 2.
If pre-emphasis is required, the external circuit shown in
Figure 3 is recommended.
The Op-Amp selected for this application should be of a “low
noise wide-bandwidth” type i.e. with at least 60dB of gain at
6kHz.
In addition to the components shown in Figure 2, it is
recommended that the power and V
BIAS
lines to the external
Op-Amp are decoupled to V
SS
physically close to the
amplifier,
by a 1.0µF capacitor.
Circuit References
Component
R
1
R
2
R
3
R
4
R
5
R
6
=
Value
100kΩ
390kΩ
100kΩ
10kΩ
18.0kΩ
2.7MΩ
Tolerance
=
±
10%
±
10%
±
1%
±
10%
±
1%
±
1%
C
1
C
2
C
3
C
4
C
5
C
6
=
1.0µF
6.8µF
1.0nF
1.0nF
15nF
0.1µF
±
20%
±
20%
±
1%
±
1%
±
1%
±
20%
C
7
C
8
C
9
C
10
X
1
=
0.1µF
0.1µF
1.0µF
12.0pF
4.0MHz
±
20%
±
20%
±
20%
±
1%
Layout Recommendations
Audio microcircuit performance will be affected by external
noise.
All external components should be kept as close to
the device as possible.
Tracks to the device should be kept short, particularly
the Audio and V
BIAS
inputs.
A “ground-plane” connected to V
SS
will help to
eliminate external pick-up.
Ensure that all inputs (analogue and d.c.) are free from
noise.
Xtal/clock and digital tracks should be kept well away
from analogue circuitry. Analogue inputs and outputs
should be screened wherever possible with high-level
outputs isolated from very low-level inputs.
4
CMLMICRO [ CML MICROCIRCUITS ]
