mt88l85anr1 Zarlink Semiconductor, mt88l85anr1 Datasheet - Page 10

• Manufacturer Part Number: mt88l85anr1
• Description: 3 V Integrated Dtmf Transceiver With Power-down And 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.
Burst Mode
In certain telephony applications it is required that DTMF signals being generated are of a specific duration
determined either by the particular application or by any one of the exchange transmitter specifications currently
existing. Standard DTMF signal timing can be accomplished by making use of the Burst Mode. The transmitter is
LEVEL
(dBm)
-25
= Reject
= May Accept
= Accept
Figure 10 - Figure 9 - Spectrum Plot
Figure 9 - Call Progress Response
0
Zarlink Semiconductor Inc.
MT88L85
250
FREQUENCY (Hz)
10
Scaling Information
10 dB/Div
Start Frequency = 0 Hz
Stop Frequency = 3400 Hz
Marker Frequency = 697 Hz and
1209 Hz
500
750
Data Sheet