
Preliminary
DSP for Digital Answering phone with FLASH interface
KS16121
TABLE 1. Definition of DTMF Detection Result
The performance of the DTMF detection is summarized in the following table.
TABLE 2. DTMF Detection Performance
In Table 2 and 3, 0 dBm is equivalent to the power of a sinusoid with a peak-to-peak amplitude of 7175 after
μ
-law to linear conversion. The KS16121 has a programmable call progress tone detector with two output flags.
The first one is the continuous tone flag that is set when a signal has a dominant signal energy in the
frequency band the user chooses. The second flag indicates whether the input tone meets the ON/OFF interval
requirement.
During a cold start, the KS16121 sets up the call progress detector such that it can detect both the busy and
dial tones. The default set-up of the call progress tone detector may be changed by loading a new filter setting
through the host interface.
The performance of the default call progress detector is summarized in the following table :
Bits
DTMF Code
Freq. 0 ( Hz)
Freq. 1 (Hz)
0x0
none
1
697
1209
0x1
0x2
0x3
0x4
0x5
0x6
0x7
0x8
0x9
0xa
0xb
0xc
2
3
4
5
6
7
8
9
*
0
#
697
1336
697
770
1477
1209
770
770
1336
1477
852
852
1209
1336
852
941
1477
1209
941
1336
941
1477
Parameter
MIN.
MAX.
UNIT
Detection signal level
DTMF Twist ( high/ low )
Detection bandwidth
Noise tolerance ( SNR )
Tone duration
Interdigit pause
-35
12
40
40
0
3
+4/-8
dBm
dB
%
dB
ms
ms