GB2278754A - Telephone instrument - Google Patents

Abstract

A telephone instrument, includes a digital signal processor 14 for processing received and transmitted speech signals, analogue-to-digital conversion means 15, 21, 27 for converting analogue speech signals to corresponding digital signals for input to the processor and digital-to-analogue conversion means 16, 22 for reconverting digital signals output by the processor to corresponding analogue signals. The processor is line powered and is programmed to provide impedance and bandwidth matching with the instrument speech transducers. In one embodiment, the processor includes means for monitoring the magnitude of the line current whereby to switch to a basic telephone function when this current falls below a predetermined value. <IMAGE>

Description

TELEPHONE INSTRUMENT This invention relates to telephone instruments and in particular to a circuit arrangement for the operation of a telephone instrument.

The conventional electronic telephone employs a number of integrated circuits that provide the various telephony functions.

Typically the circuitry must provide power supply, dialler and speed functions. This necessitates the provision of a number of integrated circuits, each dedicated to a particular function, together with associated circuitry. The assembly is generally provided on a printed circuit board.

A significant problem in designing and manufacturing electronic telephones is that of meeting the different requirements of the different national telephone administrators. For example there are different requirements on the impedance and bandwidth of the instrument transducer. There may also be different signalling requirements. For this reason it is currently necessary to design different circuit constructions to meet these various requirements.

This carries a corresponding penalty in the costs of design and manufacture.

The object of the invention is to minimise or to overcome this disadvantage.

According to one aspect of the invention there is provided a telephone instrument including transducers for the reception and transmission of speech signals and a digital signal processor for processing the received and transmitted speech signals, the processor having means for matching the impedance and bandwidth characteristics of the transducers.

According to another aspect of the invention there is provided a telephone instrument including a digital signal processor for processing received and transmitted speech signals, analogue-todigital conversion means for converting analogue signals to corresponding digital signals for input to the processor, and digitalto-analogue conversion means for reconverting digital signals output by the processor to analogue signals.

According to a further aspect of the invention there is provided a telephone instrument, including a digital signal processor for processing received and transmitted signals, means for powering the digital signal processor from the line, and means responsive to the magnitude of the line current whereby, in use, to by-pass the signal processor and provide a basic telephone function when the line current is less than a predetermined value.

The instrument is suitable for use both in public and private telephone networks.

An embodiment of the invention will now be described with reference to the accompanying drawing in which the single figure represents a processor controlled telephone circuit arrangement.

Referring to the drawing, the circuit arrangement interfaces with the line L via an electronic hookswitch 11 and rectifier bridge 12.

Power for operation of the circuit is extracted from the line via a power extraction transmitter circuit 13. This circuit also monitors the available line current and generates a default signal if this line current is lower than a preset value.

The circuit is controlled by a digital signal processor (DSP) 14 which is supplied with power, e.g. at a regulated supply voltage of 3 volts, from a switched mode power supply (SMPS) 23 coupled to the power extraction/transmitter circuit 13. The DSP provides both signal processing and line signalling functions. A further, free running, switched mode power supply 26 is coupled to the line L via a DC blocking capacitor C1 is initiated by the presence of ringing voltage on the line. This provides sufficient power both to operate the DSP14 during ringing and to operate a loudspeaker 18 which, in the ringing mode, functions as a tone ringer.

In the dialling mode of the instrument, the DSP decodes signals from the keypad 25 and generates digital codes corresponding either to MF or loop disconnect dial signals for output to the line via a first digital to analogue converter 22 and the power extraction/transmitter circuit 13.

Received analogue signals from the line, e.g. speech signals, are fed to a first analogue to digital converter 15 whose digital output is fed to the digital signal processor The DSP 14 outputs processed received speech signals via a second digital to analogue converter 16 to the handset earpiece 17 and/or to the loudspeaker 18 providing hands-free operation.

Transmitted speech signals from the handset microphone 19 and/or a hand-free microphone 20 are fed via a second analogue to digital converter 21 to the DSP 15. These signals are processed and output via the first digital to analogue converter 22 to the power supply/transmitter circuit 13 for transmission to the line.

Typically the DSP 15 performs the following functions:1. Interface to keyboard 2. Interface to display 3. Generation of VF tones and LD pulses 4. Sidetone balance 5. Line loss gain regulation including HF compensation on long lines 6. Enhancing audio bandwidth of received speech by prediction of missing sounds 7. Noise cancellation and background noise control on handset microphone 8. Enhanced loudness ratings for users with poor hearing 9. Handsfree using partial adaptive echo cancelling and partial switching 10. Flattening of poor frequency response of cheap loudspeaker/ case combination.

11. Ring detection/tinkle suppression and programmable tone generation 12. CLASS decode 13. Clock and timer functions In particular, the DSP may be programmed to match the microphone, earpiece and loudspeaker impedances/characteristics required by a particular telephone administration. In this way the same circuit construction may be employed for use in a wide variety of administrations, the only significant change being in the DSP programming software. This results in a significant reduction in manufacturing costs.

In a further embodiment the DSP may incorporate software which effects measuring of the above mentioned transducer impedances and characteristics whereby to adapt the DSP response to those transducers. A single software package can then be employed for all the major telephone administrations.

In some applications, an off-chip EEPROM (not shown) may be used to store e.g. value control settings, line current information for parallel detection and a memory for the dialler.

that signal the DSP operates switches S1, S2 and S3 whereby the instrument is switched to operation via a parallel operation sidetone circuit 24. In this condition the telephone reverts to a Plain Old telephone (POT) with an external sidetone network optimised for parallel operation. Low line current conditions may occur e.g.

during parallel operation over a long line or subscriber loop.

Claims (5)

1. A telephone instrument, including a digital signal processor for processing received and transmitted speech signals, analogue-to-digital conversion means for converting analogue speech signals to corresponding digital signals for input to the processor, digital-to-analogue conversion means for reconverting digital signals output by the processor to corresponding analogue signals, and means associated with the processor for providing impedance and bandwidth matching with the instrument speech transducers.

2. A telephone instrument as claimed in claim 1, wherein the digital signal processor has means for drawing power from the line.

3. A telephone instrument as claimed in claim 2, wherein the digital signal processor includes means responsive to the magnitude of the line current whereby, in use, to bypass the signal processor and provide a basic telephone function when the line current is less than a predetermined value.

4. A telephone instrument as claimed in claim 3, wherein the digital signal processor is powered from the line via a switched mode supply circuit.

5. A telephone instrument substantially as described herein with reference to and as shown in the accompanying drawing.