mt9092apr1 Zarlink Semiconductor, mt9092apr1 Datasheet - Page 8

• Manufacturer Part Number: mt9092apr1
• Description: Fully Featured Digital Telephone Circuit With Embedded Hdlc Transceiver And Dsp For Tone Generations And Hands Free Operation
• Manufacturer: Zarlink Semiconductor

Optional Offset Nulling
Transmit PCM may contain residual offset in the form of a DC component. An offset of up to ±fifteen linear bits is
acceptable with no degradation of the parameters defined in CCITT G.714. The HPhone-II filter/CODEC
guarantees no more than ±ten linear bits of offset in the transmit PCM when the autonull routine is not enabled. By
enabling autonulling (see AUTO in the Receive Gain Control Register, address 1Dh) offsets are reduced to within
±one bit of zero. Autonulling circuitry was essential in the first generations of Filter/Codecs to remove the large DC
offsets found in the linear technology. Newer technology has made nulling circuitry optional as offered in the
HPhone-II.
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.
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.
DTMF Signal to distortion:
The sum of harmonic and noise power in the frequency band from 50 Hz to 3500 Hz is typically more than 30 dB 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
1209
1336
1477
1633
(Hz)
697
770
852
941
COEFF = 0.128 x Frequency (in Hz)
Table 1 - DTMF Frequencies
Zarlink Semiconductor Inc.
COEF
ABh
BDh
6Dh
9Bh
D1h
59h
63h
79h
MT9092
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