Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By amplitude
Reexamination Certificate
2000-02-24
2001-05-22
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By amplitude
C327S066000, C327S108000, C327S563000
Reexamination Certificate
active
06236242
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a line receiver circuit for receiving differential signals from a symmetrical transmission line. A line receiver circuit of this kind is known from WO 95 17763.
A line receiver circuit serves to receive signals from a transmission line. Differential signal transmission over a symmetrical transmission line means that the signals to be received at an input of the line receiver do not necessarily use a well defined potential of the line receiver circuit, e.g. its ground potential, as a reference but use a potential of a second line receiver input as a reference.
The common mode voltage on the transmission line, as seen by the line receiver, can not always be confined to a well defined voltage or limited voltage interval. This has numerous reasons. For instance, different system components interconnected by a symmetrical transmission line, can have an offset in their respective ground reference potentials. Another reason can be, that the line receiver circuit must fulfill the design objective to cooperate with a number of different signal transmission standards each providing a different common mode voltage level.
In reality, however, a line receiver circuit will not be able to operate with common mode voltages over an arbitrary large range. If the common mode voltage on the transmission line exceeds the limits of the common mode voltage range of the line receiver, the reception of signals from the transmission line will become unreliable or impossible. Therefore it is desirable to provide a line receiver circuit with a common mode input voltage range as large as possible.
In order to achieve this, from WO 95 17763 it is known to provide two input stages in parallel, which are designed to operate within different, partially overlapping common mode voltage ranges. If the common mode voltage at the input of that circuit reaches a predetermined level where the second input circuit can operate, the first input circuit is disabled in order to avoid that both input stages simultaneously drive a subsequent stage, because this might result in an undesirable dependency of the overall signal delay on the input common mode voltage level. The circuit according to this document achieves a takeover between said first and said second stage in a lower region of the overall common mode voltage operating range.
It is the object of the present invention, to provide a line receiver circuit with a large common mode operating range such that a take over between said first stage and said second stage takes place in a higher region of the overall common mode operating range.
SUMMARY OF THE INVENTION
According to the present invention, this object is solved as defined in claim
1
. Advantageous embodiments of the invention are given in the dependent claims.
A line receiver circuit in accordance with the present invention achieves a large common mode voltage operating range by means of providing more than one input stages each interfacing with the transmission line. Each input stage is adapted to operate within a common mode voltage range specific to the particular stage. The input stages are provided such that their common mode voltage operating ranges partially overlap each other, such that an increased common mode operating range is obtained. The signals output by each input stage are suitably combined. The activation of the second stage is performed by detecting an actual operating condition of the first stage which depends on the input common mode level. The second stage is activated only if the detected operating condition of said first stage indicates that the common mode voltage level approaches a limit of the common mode operating range of said first stage.
Preferably, said first stage is adapted to operate in a lower common mode operating region, and the second stage is adapted to operate in a higher common mode operating region.
According to a preferred embodiment, the line receiver circuit includes a first input stage comprising a floating current mirror for a lower common mode voltage range, and a second input stage comprising a voltage difference amplifier for an upper common mode voltage range. The outputs of the first input stage and the second input stage are connected to operate on the same load elements to obtain a combined output signal.
Preferably, said means for activating and disabling, respectively, said second input stage can gradually enable the second input stage as soon as the common mode input voltage reaches to or beyond the limits of the common mode voltage range of the first input stage, and otherwise keeps the second input stage disabled.
In the following, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
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Cunningham Terry D.
Nguyen Long
Nixon & Vanderhye P.C.
Telefonaktiebolaget LM Ericsson (publ)
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