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MT9196

ISO2-CMOS Integrated Digital Phone Circuit (IDPC)

Zarlink Semiconductor Inc 

MT9196

Data Sheet

Since the received digital gain control is used to set the listening level of the received speech, for both handset

receiver and loudspeaker, it is necessary to provide additional gain in the loudspeaker path so that its receive level

can be controlled independently from the receiver output. The Gain0 to Gain3 control bits (address 0Bh) are used

to boost the loudspeaker output to a comfortable listening level for the third parties in group listening. Generally the

Gain3 bit should be set to logic 1 in this mode. This increases the gain programmed via the Gain0 - Gain2 bits by a

factor of 8 dB. In group listening a speaker gain setting of 4 to 16 dB will be required to set a comfortable group

listening level after the handset user has adjusted their listening level as required.

Since the anti-howling circuit has dynamic control over the transmit and receive gain control registers, it is

recommended that this function be turned off momentarily when DTMF tone generation is required. This will ensure

that the proper transmit levels are attained.

Transmit Noise Reduction (squelch)

The transmit signal may be muted to eliminate transmission of excessive background noise.

In this mode the signal level in the transmit path is compared with the high level threshold stored at address 1Dh.

When the transmit signal level exceeds this threshold no loss is inserted into the transmit path. After exceeding the

high level threshold the transmit signal level is then compared to a low level threshold stored at address 1Eh. When

the transmit signal level falls below this threshold the transmit digital gain is reduced by the programmed amount

(Pad0-2) and comparison reverts back to the high threshold level. The receive path gain is not altered by transmit

noise reduction.

Receive Noise Reduction (squelch)

The receive signal may be muted to eliminate background noise resulting from a poor trunk connection.

In this mode the signal level in the receive path is compared with the high level threshold stored at address 1Dh.

When the receive signal level exceeds this threshold no loss is inserted into the receive path. After exceeding the

high level threshold the receive signal level is then compared to a low level threshold stored at address 1Eh. When

the receive signal level falls below this threshold the receive digital gain is reduced by the programmed amount

(Pad2-0) and comparison reverts back to the high threshold level. The transmit path gain is not altered by receive

noise reduction.

Tx/Rx Switched Loss

In this mode the programmed switched loss is inserted into either the transmit or receive path dependent only upon

activity in the receive path. If receive path activity is above the programmed high level threshold then the switched

loss is inserted into the transmit path. If receive path activity is below the programmed low level threshold then the

switched loss is inserted into the receive path.

This mode can be used to implement a loudspeaking function where the receive audio is routed to the SPKR± pins

and transmit audio is sourced from the MIC+ pin. In this mode there is no algorithmic cancellation of echo so it is

recommended that this switched loss program be used only in 4-wire systems (i.e., digital set to digital set).

Transducer Interfaces

Four standard telephony transducer interfaces plus an auxiliary I/O are provided by the IDPC. These are:

• The handset microphone inputs (transmitter), pins M+/M- and the answerback microphone input MIC+. The

nominal transmit path gain may be adjusted to either 6.0 dB or 15.3 dB. Control of this gain is provided by

the TxINC control bit (Control register 2, address 0Fh). This gain adjustment is in addition to the

programmable gain provided by the transmit filter and Digital Gain circuit.

• The handset speaker outputs (receiver), pins HSPKR+/HSPKR-. This internally compensated, fully differential

output driver is capable of driving the load shown in Figure 4. The nominal handset receive path gain may be

adjusted to either -12.1 dB or -9.6 dB. Control of this gain is provided by the RxINC control bit (Control

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Zarlink Semiconductor Inc.

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