Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Amplitude control
Reexamination Certificate
1997-10-30
2001-07-10
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Amplitude control
C327S322000, C327S538000, C326S030000, C326S086000, C330S157000
Reexamination Certificate
active
06259298
ABSTRACT:
TECHNICAL FIELD
The invention relates, generally, to an arrangement for adapting, from a DC point of view, a first circuit to at least one second circuit and, more specifically, to an arrangement for adapting, from a DC point of view, the signal input terminal of a first circuit, lying at a first DC reference level, to the signal output terminal of at least one second circuit, lying at a second DC reference level.
BACKGROUND
On e.g. line interface boards provided with line interface circuits and code converters, the signal input terminals of the line interface circuits as well as the signal output terminals of the code converters were earlier related to ground which enabled a direct connection between the signal input terminal of a line interface circuit and the signal output terminal of a code converter. However, modern code converters have a reference voltage for their signal output terminal somewhere between ground and +5 V, most often around 2.25 V, while the signal input terminal of the line interface circuits lies at ground potential. If a line interface circuit whose signal input terminal lies at ground potential, is interconnected with a code converter whose signal output terminal lies at 2.25 V, an offset current is obtained in the line current outputted by the line interface circuit. Upon a polarity reversal of the line current, this offset current will maintain its polarity. Thus, different line currents are obtained for normal and reversed polarity, respectively, of the line current. Also, the offset current can cause other problems.
One way solving this problem is to interconnect a coupling capacitor between the signal input terminal of the line interface circuit and the signal output terminal of the code converter. However, this coupling capacitor has to be large in order for the system not to become unstable.
SUMMARY
The object of the invention is to generally adapt, from a DC point of view, the signal input terminal of a first circuit, e.g. a line interface circuit, lying at a first DC reference level to the signal output terminal of at least one second circuit, e.g. a code converter, lying at a second DC reference level without the use of any coupling capacitor.
This is attained according to the invention in that a DC current is deliberately allowed to flow in the signal input terminal of the first circuit, the effect of this current being eliminated in the first circuit by generating a corresponding current of opposite polarity.
More in detail, this object is attained in accordance with the invention mainly in that the signal input terminal is adapted to be virtually short-circuited to the first DC reference voltage level which is of a predetermined value separate from zero, that the signal input terminal is connected, via a respective first resistance, to the respective signal output terminal, whereby first DC currents will be allowed to flow through the respective first resistance, that the signal input terminal is connected to ground via a selectable, second resistance, whereby a second DC current will flow through the second resistance which is to be selected in such a manner that the DC current sum formed by the first DC currents and the second DC current in the signal input terminal of the first circuit, amounts to a predetermined value, and the line interface circuit is adapted to internally generate a DC cancellation current corresponding to the DC current sum but being of opposite polarity in order to eliminate the effect of the DC current sum.
Hereby, the need of a coupling capacitor between the signal input terminal of the first circuit and the signal output terminal of the respective second circuit, will be eliminated. Thus, the first circuit will be easily adaptable to the second circuits by a suitable selection of the resistance connected to ground.
REFERENCES:
patent: 5321324 (1994-06-01), Hardee et al.
patent: 5486778 (1996-01-01), Lou
patent: 5541531 (1996-07-01), Kultgen
patent: 5604450 (1997-02-01), Borkar et al.
patent: 5731711 (1998-03-01), Gabara
N.I. Lavrantiev, “Simple DC Modulator” Electronics World + Wireless World, vol. 100, p. 68 (Jan. 1994).
Eriksson Hans
Larsson Elisabeth
Burns Doane Swecker & Mathis L.L.P.
Callahan Timothy P.
Nguyen Minh
Telefonaktiebolaget LM Ericsson (publ)
LandOfFree
Method and an arrangement for adapting from a DC point of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and an arrangement for adapting from a DC point of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and an arrangement for adapting from a DC point of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2528767