Telephone line interfacing circuit used for both voice and...

Details Telephone line interfacing circuit used for both voice and... Telephone line interfacing circuit used for both voice and...

1997-05-14

2002-06-18

Kuntz, Curtis (Department: 2643)

Telephonic communications

Telephone line or system combined with diverse electrical...

Having transmission of a digital message signal over a...

C379S100090, C379S100140

Reexamination Certificate

active

06408057

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a telephony communication device, and, in particular, to a line interface circuit for interfacing telephone systems. The line interface enables both voice and non-voice operations at a telephone terminal with a common design. The present invention further relates to a method for controlling the line interfacing circuit.
2. Description of the Related Art
Circuits have been developed to interface communications devices with a telephone exchange system, such as a transmitter/receiver circuit in a standard telephone. Some communications devices, such as a conventional facsimile machine, are designed for both voice and non-voice communications. In one mode, the facsimile machine transmits and receives images of documents or still pictures via a telephone line. Hence, the facsimile machine includes an interfacing circuit having an image processing unit for scanning and digitizing the documents and pictures for transmission via the telephone line. In a second mode, the facsimile machine can be used for voice communications for enabling a user to orally communicate with the intended recipient of the facsimile. Hence, the facsimile machine also includes a voice processing unit, generally within the interfacing circuit, for digitizing sound.
With reference to
FIG. 1
there is shown a block diagram of a conventional facsimile machine. The facsimile machine includes a central processing unit or CPU
FAX
101
which controls the operations of the facsimile machine, such as transmitting, receiving and copying. The CPU
FAX
101
may be provided with an associated RAM memory and stored operating program for operating the facsimile machine or CPU
FAX
101
may be connected to an external memory
109
. The CPU associated RAM may also store other data including data generated during the execution of the operating program.
An operating panel (OPE)
102
which includes a key matrix having a plurality of keys and a display unit is coupled to the CPU
FAX
101
. The key matrix includes circuitry for generating at least one signal when a user depresses one of the keys to set a desired operational mode and/or to initiate an operation. Circuitry associated with the display unit of the OPE
102
receives the at least one signal from the control unit
101
and displays an appropriate display element such as LCD(s) indicative of the operational mode or operation being executed by the facsimile machine.
The facsimile machine further includes a sensor unit
103
, a scanner
104
and an image processing unit
105
. The sensor unit
103
senses the placement of a document in the facsimile machine and whether there is printing paper and generates appropriate signals which are transmitted to the CPU
FAX
101
. The scanner
104
scans the document and converts the scanned image into digital data which are sent to the image processing unit
105
. The image processing unit
105
processes the digital data and transmits the data via a telephone line to a receiving facsimile machine or other communication device.
A printing unit
106
is also coupled to the CPU
FAX
101
for printing image data during the receiving or copying operations. The facsimile machine further includes a modem
107
(a non-voice terminal) for performing data communications via a telephone line. In a transmitting mode, the modem
107
modulates the digital data received from the image processing unit
105
and transmits the modulated data under the control of the CPU
FAX
101
. In a receiving mode, the modem
107
demodulates coded image signals received via the telephone line to re-create the original document data.
A line interface unit (LIU)
108
is coupled between the modem
107
and the telephone line. The LIU
108
establishes a channel between the modem
107
and the telephone line to facilitate: interfacing the telephone line with the modem
107
; interfacing the telephone line with a telephone handset; processing of a ring signal received from an exchange system; and telephone dialing operations. The LIU
108
has a tip terminal T and a ring terminal R which are coupled to the telephone line. The above-mentioned functions of the LIU
108
will now be described with reference to FIG.
2
.
First, the function of interfacing the telephone line with the modem
107
will be described.
In facsimile data communications, a non-voice path (NVP) is selected by switch unit
110
in response to a switch control signal S
1
received from the CPU
FAX
101
to trip a switch therein to couple the tip terminal T and ring terminal R to the modem
107
via a first dialer
120
and a first LIU
130
to establish a DC loop. The first LIU
130
serves to transmit signals such as modulated facsimile signals and dual tone multi-frequency (DTMF) dial signals generated from the modem
107
to the telephone line. The first dialer
120
generates the dial pulses.
In addition to selecting a non-voice path, the switch unit
110
can select a voice path (VP) along a second LIU
135
, a speech network
150
and a handset
180
to perform a telephone hook switching function. This is accomplished by transmitting a control signal S
2
from the CPU
FAX
101
to the first dialer
120
to cut-off the DC loop and generate dial pulses. The first LIU
130
serves to keep an AC impedance matching with telephone exchange system EXH by carrying out primary/secondary separating functions, an AC signal coupling function, and a DC masking function.
The function of interfacing the telephone line with the telephone handset
180
to perform voice communications will now be described with respect to the CPU
FAX
101
being in a power-on state and in a power-off state. When the user lifts the handset
180
the facsimile is thrown into a DTMF dial mode and the CPU
FAX
101
is in the power-on state. In the DTMF dial mode, the speech network
150
can perform various functions such as an inter-conversion between speech signals and electrical signals, inter-conversion between two-wire signals and four-wire signals, AC impedance matching, a DC masking, and a speech transmitting and receiving function. The power-on state is sensed by a hook detector (not shown) which sends a hook-off status signal to the CPU
FAX
101
to thereby prepare the modem
107
for a dialing operation via depression of keys on key matrix
250
. If the user does not lift the handset, the facsimile is in a dial pulse (DP) dial mode and the CPU
FAX
101
controls the first dialer
120
to ready itself for a dialing operation.
In the power-off status of the CPU
FAX
101
, i.e., when the facsimile machine is in a non-operational mode or emergency mode, a separate hook switch (not shown) connected to the switch unit
110
is mechanically tripped upon lifting of the handset
180
to couple the telephone line to the speech network
150
. A bridge diode may be utilized to supply regulated electric power to the telephone line despite variations in the polarity of the electric power.
The dialing operation is initiated by switching the second dialer
170
to the DTMF/DP dial mode by lifting the handset
180
as noted above. The second dialer
170
is supplied with electric power from the speech network
150
for converting dial data received from the key matrix
250
in a form corresponding to the DTMF/DP dial mode. The converted data from the second dialer
170
is then sent to the speech network
150
for the dialing operation.
The LIU
108
of
FIG. 2
is uneconomical and inefficient in terms of its circuit configuration since it has an overlapping design. The LIU
108
uses two dialers
120
and
170
, two line interface units
130
and
135
, and overlapping DC masking circuits. In addition, there are problems regarding the various functions of the LIU
108
.
First, there is a problem regarding the function of interfacing the telephone line with the modem
107
and the telephone handset
180
. Since the modem
107
and the speech network
150
have AC impedance and DC masking circuits, respectively, the modem
107
exhibits AC impedance

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