Telephonic communications – Subscriber line or transmission line interface
Patent
1997-05-07
1999-05-04
Hunter, Daniel S.
Telephonic communications
Subscriber line or transmission line interface
379402, H04M 100
Patent
active
059012218
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND
The invention relates to a driving stage for driving the two differential amplifier output stages of a subscriber line interface circuit, said driving stage being adapted to generate four driving currents in dependence on, on the one hand, transversal and longitudinal signals IT and IL, respectively, incoming to the driving stage and, on the other hand, a reference current IR, and to supply these driving currents in pairs to the two inputs of the differential amplifier output stages.
A purpose of a subscriber line interface circuit is, among others, to supply a subscriber line with current.
In a switching centre, the subscriber lines are in an idle condition during most of the time, i.e. the lines are open. Since the power losses in the subscriber line interface circuits constitute a considerable portion of the total power loss of the switching centre, it is very important to keep the power losses in the subscriber line interface circuits as low as possible in idle condition as well as during a call.
Normally, the output stages of analogue subscriber line interface circuits are of push-pull-type and operate in class-AB, which means that a certain idle current flows through the same.
Traditionally, the output stages of analog subscriber line interface circuits have been driven by means of current from two driving stages which normally operate between ground or +5V and battery voltage which nominally is -48V in connection with telephony. In order to obtain sufficient linearity in the driving of the output stages, the driving stages usually are designed to work in class-A which means that an idle current always will flow in the driving stages from ground or +5V to the battery voltage. This idle current has to be large enough in order to be able to drive the output stages to the maximum output current that is required, and is therefore dependent on the current amplification of the output stages.
Thus, relatively large currents which are independent of each other flow from ground or +5V to the battery voltage through driving stages and output stages also when the subscriber line interface circuit is not supplying any current. In this idle condition, it is of great importance that the power consumption of the subscriber line interface circuit is low. Considerable contributions are provided by the idle current of the driving stages as well as of the output stages.
Therefore, in the idle condition, the power loss caused by the driving stages and the output stages should be as low as possible.
Moreover, it is of great importance that the driving stages are able to drive the respective output stage across all of the available voltage range.
SUMMARY
An object of the invention is therefore to bring about a driving stage which in combination with the output stage causes a lower power consumption than driving stages known so far at the same time as operation is enabled across all of the voltage range available.
This is attained by means of the driving stage according to the invention in that all four driving currents are larger than zero.
BRIEF DESCRIPTION OF THE DRAWING
The invention will be described more in detail below with reference to the appended drawing on which the single FIGURE shows an embodiment of a driving stage according to the invention for driving the two differential amplifier output stages of a subscriber line interface circuit.
DETAILED DESCRIPTION
Generally denoted 1, the drawing shows a driving stage for driving the two differential amplifier output stages 2 and 3 of a subscriber line interface circuit, not shown in any greater detail, for supplying a subscriber line comprising two wires A and B and being terminated by a load 4, e.g. a subscriber's station.
In the embodiment shown, the driving stage 1 comprises a current-mirroring circuit SSL for mirroring a longitudinal signal or current IL arriving at the driving stage 1, a current-mirroring circuit SST for mirroring a transversal signal or current IT arriving at the driving stage 1, a differential amplifier DFL which is conn
REFERENCES:
patent: 4535303 (1985-08-01), Schoofs et al.
patent: 4709388 (1987-11-01), Defretin
patent: 4782507 (1988-11-01), Siligoni et al.
patent: 4841175 (1989-06-01), De Man et al.
patent: 5526425 (1996-06-01), Meyer et al.
patent: 5596637 (1997-01-01), Pasetti et al.
patent: 5649009 (1997-07-01), Enriquez et al.
Eriksson Hans Oskar
Hellberg Henrik Helmer
Larsson Elisabeth Maria
Malmgren Carl-Henrik
Appiah Charles N.
Hunter Daniel S.
Telefonaktiebolaget LM Ericsson
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