mt88l89asr1 Zarlink Semiconductor, mt88l89asr1 Datasheet - Page 9

• Manufacturer Part Number: mt88l89asr1
• Description: 3 V Integrated Dtmf Transceiver With Adaptive Micro Interface
• Manufacturer: Zarlink Semiconductor

The period of each tone consists of 32 equal time segments. The period of a tone is controlled by varying the length
of these time segments. During write operations to the Transmit Data Register the 4 bit data on the bus is latched
and converted to 2 of 8 coding for use by the programmable divider circuitry. This code is used to specify a time
segment length, which will ultimately determine the frequency of the tone. When the divider reaches the appropriate
count, as determined by the input code, a reset pulse is issued and the counter starts again. The number of time
segments is fixed at 32, however, by varying the segment length as described above, the frequency can also be
varied. The divider output clocks another counter, which addresses the sinewave lookup ROM.
The lookup table contains codes which are used by the switched capacitor D/A converter to obtain discrete and
highly accurate DC voltage levels. Two identical circuits are employed to produce row and column tones, which
are then mixed by using a low noise summing amplifier. A bandwidth limiting filter is incorporated and serves to
attenuate distortion products above 8 kHz. Figure 9 shows that the distortion products are very low in amplitude.
LEVEL
(dBm)
-25
= Reject
= May Accept
= Accept
Figure 10 - Call Progress Response
0
Figure 9 - Spectrum Plot
Zarlink Semiconductor Inc.
MT88L89
250
FREQUENCY (Hz)
9
Scaling Information
10 dB/Div
Start Frequency = 0 Hz
Stop Frequency = 3400 Hz
Marker Frequency = 697 Hz and
1209 Hz
500
750
Data Sheet