Application Information ......
Controlled Sensitivity Setting ......
With the external gain (sensitivity) components employed as shown in Figure 2 the gain of the input stages is
19.8dB (12kHz) or 20.5dB (16kHz). For controlled sensitivity setting the gain of each bandpass filter, and hence
the device sensitivity, is adjusted by the applied serial bits D
1
to D
5
.
In the Controlled Sensitivity mode the system frequency is selected by bit D
0
(‘1’ = 12kHz; ‘0’ = 16kHz). Data is
loaded Bit 5 (D
5
) first.
Table 2 details the serial data input to produce the required sensitivity. Minimum, Nominal and Maximum
Sensitivity figures are provided to make complete allowance for internal circuit offsets and component tolerances.
0dB(ref.) = 775mVrms at V
DD
= 5.0 volts; varies directly with V
DD
.
Examples are provided as a guide to meeting national specifications.
German FTZ Specification
16kHz
This system has a Must Decode level of -21dB(ref.)
and a Must-Not Decode level of -27dB(ref.). Reference
to Table 2 shows that Bandpass Filter Gain settings of
5dB, 6dB or 7dB will enable an FX641 channel to meet
this level specification.
Figure 6 illustrates the range of these various settings.
Hence to meet the German FTZ specification, the
input data (D
5
to D
0
) can be:
00101 0
5.0dB
or
00110 0
6.0dB
or
00111 0
7.0dB
Selecting the middle setting would give the greatest
noise immunity.
MUST DECODE
-21dB(ref.)
-21.9
WILL DECODE
-23.2 5.0dB
-22.9
-23.9
-24.2 6.0dB
-24.5
-25.5
WILL-NOT DECODE
-25.2 7.0dB
-26.5
MUST-NOT DECODE
-27dB(ref.)
Fig.6 German Specification -Possible Settings
MUST DECODE
-17.36dB(ref.)
-18.2
WILL DECODE
-19.2
-19.5 2.0dB
-20.2
-20.8
-20.5 3.0dB
-21.8
WILL-NOT DECODE
-21.5 4.0dB
-22.8
MUST-NOT DECODE
-23.8dB(ref.)
French Specification
12kHz
This system has a Must Decode level of
-17.36dB(ref.) and a Must-Not Decode level of
-23.8dB(ref.). Reference to Table 2 shows that
Bandpass Filter Gain settings of 2dB, 3dB or 4dB will
enable an FX641 channel to meet this level
specification.
Fig 7 illustrates the range of these various settings.
Hence to meet the French SPM specification, the
input data (D
5
to D
0
) can be:
00010
1
2.0dB
or
00011 1
3.0dB
or
00100
1
4.0dB
Selecting the middle setting would give the greatest
noise immunity.
Fig.7 French Specification -Possible Settings
System
Select
X
X
0
1
0
1
X
Preset
Level
0
0
1
1
1
1
X
Output
Select
0
1
0
0
1
1
X
Output
Enable
0
0
0
0
0
0
1
Operating Mode
Packet Mode Output;
Serial Data Control
Tone Follower Output;
Serial Data Control
Packet Mode Output;
Preset Sensitivity 16kHz
Packet Mode Output;
Preset Sensitivity 12kHz
Tone Follower Output;
Preset Sensitivity 16kHz
Tone Follower Output;
Preset Sensitivity 12kHz
Tristate Output
High Z
Table 3 Operating Mode Configurations
X = don't care
CMLMICRO [ CML MICROCIRCUITS ]
