AMBE2000 datasheet(31/47 Pages) ETC

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AMBE-2000™ Vocoder Chip

User’s Manual Version 3.0

page 31

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Table 5-K DTMF Tone Detection Parameters

DTMF Tone

Detection

Requirement

Value

Description

Minimum

Input Level

-25 dBm0

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).

Minimum

Signal to Noise

Distortion ratio

15 dB

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.

Minimum

Frequency

Tolerance

±1.5%

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.

Maximum

Frequency

Tolerance

±3.5%

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.

Normal Twist

Range

8-10 dB

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.

Reverse Twist

Range

4-10 dB

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.

Minimum

Tone Duration

45 mS

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

LSB

DTMF Amplitude

DTMF Digit Detect/ Generate

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