Application Information ......
Sensitivity Setting
To enable the FX641 to operate correctly to most national 12kHz and 16kHz SPM specifications, the input
sensitivity can be accurately adjusted and set.
There are two different pin-selectable modes of sensitivity setting available to the FX641: Controlled Sensitivity
Mode and Fixed Sensitivity Mode
The Controlled Sensitivity mode allows the sensitivity setting from a µController via a 6-bit serial data input. This
same serial input also sets operation (bit 0) to either 12kHz or 16kHz systems. Both channels are set identically.
The Fixed Sensitivity mode allows the sensitivity of each channel to be set to a fixed “gain” by external
components at the input amplifiers. Operation to either 12kHz or 16kHz is by the System Select input.
Controlled Sensitivity Setting
12kHz System
Bit D
0
= ‘1’
Minimum Nominal Maximum
Sensitivity Sensitivity Sensitivity
dB(ref.)
dB(ref.)
dB(ref.)
-16.2
-17.2
-18.2
-19.2
-20.2
-21.2
-22.2
-23.2
-24.2
-25.2
-26.2
-27.2
-28.2
-29.2
-30.2
-31.2
-32.2
-33.2
-34.2
-35.2
-36.2
-37.2
-38.2
-39.2
-40.2
-41.2
-42.2
-43.2
-17.5
-18.5
-19.5
-20.5
-21.5
-22.5
-23.5
-24.5
-25.5
-26.5
-27.5
-28.5
-29.5
-30.5
-31.5
-32.5
-33.5
-34.5
-35.5
-36.5
-37.5
-38.5
-39.5
-40.5
-41.5
-42.5
-43.5
-44.5
-18.8
-19.8
-20.8
-21.8
-22.8
-23.8
-24.8
-25.8
-26.8
-27.8
-28.8
-29.8
-30.8
-31.8
-32.8
-33.8
-34.8
-35.8
-36.8
-37.8
-38.8
-39.8
-40.8
-41.8
-42.8
-43.8
-44.8
-45.8
16kHz System
Bit D
0
= ‘0’
Minimum Nominal Maximum
Sensitivity Sensitivity Sensitivity
dB(ref.)
dB(ref.)
dB(ref.)
-16.9
-17.9
-18.9
-19.9
-20.9
-21.9
-22.9
-23.9
-24.9
-25.9
-26.9
-27.9
-28.9
-29.9
-30.9
-31.9
-32.9
-33.9
-34.9
-35.9
-36.9
-37.9
-38.9
-39.9
-40.9
-41.9
-42.9
-43.9
-18.2
-19.2
-20.2
-21.2
-22.2
-23.2
-24.2
-25.2
-26.2
-27.2
-28.2
-29.2
-30.2
-31.2
-32.2
-33.2
-34.2
-35.2
-36.2
-37.2
-38.2
-39.2
-40.2
-41.2
-42.2
-43.2
-44.2
-45.2
-19.5
-20.5
-21.5
-22.5
-23.5
-24.5
-25.5
-26.5
-27.5
-28.5
-29.5
-30.5
-31.5
-32.5
-33.5
-34.5
-35.5
-36.5
-37.5
-38.5
-39.5
-40.5
-41.5
-42.5
-43.5
-44.5
-45.5
-46.5
Serial Data
Bits
D
5
- D
1
00
00
00
00
00
00
00
00
01
01
01
01
01
01
01
01
10
10
10
10
10
10
10
10
11
11
11
11
11
11
11
11
000
001
010
011
100
101
110
111
000
001
010
011
100
101
110
111
000
001
010
011
100
101
110
111
000
001
010
011
100
101
110
111
Bandpass
Filter Gain
(dB)
0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
12.0
13.0
14.0
15.0
16.0
17.0
18.0
19.0
20.0
21.0
22.0
23.0
24.0
25.0
26.0
27.0
These states should never be used. If senstivities of this order are required (eg. the Swedish Rural SPM
Specification), it is recommended that the Controlled Sensitivity setting is set to 20dB (1 0 1 0 0) and
external components selected to set the Input Amp gain to a higher figure.
Table 2 Controlled Sensitivity Setting Information
The figures provided in Table 2 assume:
1.
The recommended amplifier components (see Figure 2) are employed providing an amplifier gain at
16kHz of 19.8dB ±0.3dB or at 12kHz of 19.1dB ±0.3dB.
2.
A comparator sensitivity of 1.6dB(ref.) ±1dB (the variation being due to filter gain error, filter output offset,
comparator input offset or a combination of all 3).
3.
The applied V
DD
is 5.0 volts; 0dB (ref.) = 775mVrms.
CMLMICRO [ CML MICROCIRCUITS ]
