AMBE2000 Datasheet, PDF (31/47 Pages) List of Unclassifed Manufacturers – VOCODER CHIP

DTMF Tone
Detection
Requirement
Minimum
Input Level
Minimum
Signal to Noise
Distortion ratio
Minimum
Frequency
Tolerance
Maximum
Frequency
Tolerance
Normal Twist
Range
Reverse Twist
Range
Minimum
Tone Duration
AMBE-2000™ Vocoder Chip
User’s Manual Version 3.0
Table 5-K DTMF Tone Detection Parameters
Value
-25 dBm0
15 dB
±1.5%
±3.5%
8-10 dB
4-10 dB
45 mS
Description
An input signal shall not be rejected as a DTMF tone if its amplitude is greater
than -25 dBm0 (maximum sinusoid dBm0 is defined as+3.17 dBm0).
In order for an input signal to correspond to a valid DTMF tone, the ratio of
inband to out-of-band energy must be greater than 15dB. Inband energy is
defined to be the energy in frequency components within ±3.5% of the two
frequencies defined by the DTMF frequencies. Out-of-band energy is defined to
be the total energy minus in the inband energy.
An input signal shall not be rejected as a DTMF tone if both of its principal
frequency components are within ±1.5% of the frequencies needed for the DTMF
tone.
An input signal shall not be rejected as a DTMF tone if either of its principal
frequency components are outside ±3.5% of the frequencies needed for the DTMF
tone.
An input signal does not correspond to a valid DTMF tone if the energy contained
within the low frequency band is more than 10 dB greater than the energy
contained in the high frequency band. An input signal shall not be rejected as a
DTMF if energy contained within the low frequency band is less than 8 dB greater
than the energy contained in the high frequency band. Each low and high
frequency band is limited to ±3.5% of the frequencies needed for the DTMF tone.
An input signal does not correspond to a valid DTMF tone if the energy contained
within the high frequency band is more than 10 dB greater than the energy
contained in the low frequency band. An input signal shall not be rejected as a
DTMF if energy contained within the high frequency band is less than 4 dB
greater than the energy contained in the low frequency band. Each low and high
frequency band is limited to ±3.5% of the frequencies needed for the DTMF tone.
An input signal shall not be rejected as a DTMF tone as long as its time duration
is greater than 45 mS. In addition a minimum of two frames will be transmitted
of the DTMF tone if a valid tone is detected. The duration of a tone is defined by
the points at which the envelope is 20 dB below its peak value.
Table 5-L DTMF Control Format
DTMF Control – 8-bits (See Table 1-F)
15:
MSB
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0:
LSB
DTMF Amplitude
DTMF Digit Detect/ Generate
page 31
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