mt9094apr1 Zarlink Semiconductor, mt9094apr1 Datasheet - Page 4

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

MT9094
Data Sheet
The main feature required of a digital telephone is to convert the digital Pulse Code Modulated (PCM) information,
being received by the telephone set, into an analog electrical signal. This signal is then applied to an appropriate
audio transducer such that the information is finally converted into intelligible acoustic energy. The same is true of
the reverse direction where acoustic energy is converted first into an electrical analog and then digitized (into PCM)
before being transmitted from the set. Along the way if the signals can be manipulated, either in the analog or the
digital domains, other features such as gain control, signal generation and filtering may be added. More complex
processing of the digital signal is also possible and is limited only be the processing power available. One example
of this processing power may be the inclusion of a complex handsfree switching algorithm. Finally, most electro-
acoustic transducers (loudspeakers) require a large amount of power to develop an effective acoustic signal. The
inclusion of audio amplifiers to provide this power is required.
The DPhone-II features Digital Signal Processing (DSP) of the voice encoded PCM, complete Analog/Digital and
Digital/Analog conversion of audio signals (Filter/CODEC) and an analog interface to the external world of electro-
acoustic devices (Transducer Interface). These three functional blocks combine to provide a standard full-duplex
telephone conversation utilizing a common handset. Selecting transducers for handsfree operation, as well as
allowing the DSP to perform its handsfree switching algorithm, is all that is required to convert the full-duplex
handset conversation into a half-duplex speakerphone conversation. In each of these modes, full programmability
of the receive path and side-tone gains is available to set comfortable listening levels for the user as well as
transmit path gain control for setting nominal transmit levels into the network.
The ability to generate tones locally provides the designer with a familiar method of feedback to the telephone user
as they proceed to set-up, and ultimately, dismantle a telephone conversation. Also, as the network slowly evolves
from the dial pulse/DTMF methods to the D-Channel protocols it is essential that the older methods be available for
backward compatibility. As an example; once a call has been established, say from your office to your home, using
the D-Channel signalling protocol it may be necessary to use in-band DTMF signalling to manipulate your personal
answering machine in order to retrieve messages. Thus the locally generated tones must be of network quality and
not just a reasonable facsimile. The DPhone-II DSP can generate the required tone pairs as well as single tones to
accommodate any in-band signalling requirement.
Each of the programmable parameters within the functional blocks is accessed through a serial microcontroller port
compatible with Intel MCS-51 specifications.
Functional Description
In this section, each functional block within the DPhone-II is described along with all of the associated
control/status bits. Each time a control/ status bit(s) is described it is followed by the address register where it will be
found. The reader is referred to the section titled ‘Register Summary' for a complete listing of all address map
registers, the control/status bits associated with each register and a definition of the function of each control/status
bit. The Register Summary is useful for future reference of control/status bits without the need to locate them within
the text of the functional descriptions.
Filter-CODEC
The Filter/CODEC block implements conversion of the analog 3.3kHz speech signals to/from the digital domain
compatible with 64 kb/s PCM B-Channels. Selection of companding curves and digital code assignment are
register programmable. These are CCITT G.711 A-law or µ-Law, with true-sign/ Alternate Digit Inversion or true-
sign/Inverted Magnitude coding, respectively. Optionally, sign- magnitude coding may also be selected for
proprietary applications.
The Filter/CODEC block also implements transmit and receive audio path gains in the analog domain. These gains
are in addition to the digital gain pad provided in the DSP section and provide an overall path gain resolution of
0.5 dB. A programmable gain, voice side-tone path is also included to provide proportional transmit speech
feedback to the handset receiver so that a dead sounding handset is not encountered. Figure 3 depicts the nominal
half-channel and side-tone gains for the DPhone-II.
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Zarlink Semiconductor Inc.