mt9094apr1 Zarlink Semiconductor, mt9094apr1 Datasheet - Page 8

• Manufacturer Part Number: mt9094apr1
• Description: Fully Featured Digital Telephone Circuit With Embedded Dsp For Tone Generation And Hands Free Operation
• Manufacturer: Zarlink Semiconductor

DTMF and Gain Control Program
The DTMF program generates a dual cosine wave pattern which may be routed into the receive path as comfort
tones or into the transmit path as network signalling. In both cases, the digitally generated signal will undergo gain
adjustment as programmed into the Receive Gain Control and the Transmit DTMF Gain Control registers. The
composite signal output level in both directions is -4 dBm0 when the gain controls are set to 2Eh (-3.0 dB).
Adjustments to these levels may be made by altering the settings of the gain control registers. Pre-twist of 2.0 dB is
incorporated into the composite signal. The frequency of the low group tone is programmed by writing an 8-bit
coefficient into Tone Coefficient Register 1 (address 23h), while the high group tone frequency uses the 8-bit
coefficient programmed into Tone Coefficient Register 2 (address 24h). Both coefficients are determined by the
following equation:
where COEFF is a rounded off 8 bit binary integer
A single frequency tone may be generated instead of a dual tone by programming the coefficient at address 23h to
a value of zero. In this case the frequency of the single output tone is governed by the coefficient stored at address
24h.
DTMF Signal to distortion:
Table 1 gives the standard DTMF frequencies, the coefficient required to generate the closest frequency, the actual
frequency generated and the percent deviation of the generated tone from the nominal.
Tone Ringer and Gain Control Program
A locally generated alerting (ringing) signal is used to prompt the user when an incoming call must be answered.
The DSP uses the values programmed into Tone Coefficient Registers 1 and 2 (addresses 23h and 24h) to
generate two different squarewave frequencies in PCM code. The amplitude of the squarewave frequencies is set
to a mid level before being sent to the receive gain control block. From there the PCM passes through the decoder
and receive filter, replacing the normal receive PCM data, on its way to the loudspeaker driver. Both coefficients are
determined by the following equation:
where COEFF is a rounded off 8 bit binary integer
The sum of harmonic and noise power in the frequency band from 50 Hz to 3500 Hz is typically more than 30dB below the power in the tone pair.
All individual harmonics are typically more than 40 dB below the level of the low group tone.
Frequency
(Hz)
1209
1336
1477
1633
697
770
852
941
COEFF = 0.128 x Frequency (in Hz)
COEFF = 8000/Frequency (Hz)
Zarlink Semiconductor Inc.
COEF
ABh
BDh
6Dh
9Bh
D1h
59h
63h
79h
MT9094
Table 1
8
Frequency
Actual
1210.9
1335.9
1476.6
1632.8
695.3
773.4
851.6
945.3
Deviation
+.40%
+.46%
+.20%
-.20%
-.05%
-.03%
-.01%
.00%
%
Data Sheet