Transformer circuit arrangement

Details Transformer circuit arrangement Transformer circuit arrangement

2003-10-15

2004-12-07

Donovan, Lincoln (Department: 2832)

Inductor devices

Winding formed of plural coils

Two windings

C336S180000, C336S192000, C379S349000

Reexamination Certificate

active

06828893

ABSTRACT:

The invention relates to a transformer circuit arrangement which is designed, in particular, for the transmission of signals in message transmission systems or communication systems, such as, for example, xDSL systems.
The devices referred to as transformers in message transmission systems are essential passive electrical components which fulfil a wide variety of tasks such as, for example, electrical decoupling, the transforming of voltages/currents, or the changing of impedance values. Due to their large spatial requirements, their high price in comparison with other passive components, their non-linear behaviour, their losses, and the absence of integration capability, the use of such transformers is, however, to be avoided as far as possible. In many cases, it has not hitherto been possible for the transformer to be replaced by a device of equal value, with the result that it cannot be done away with.
In xDSL systems (“Digital Subscriber Line”), for example, the transformer determines the performance capacity of these systems. What is required is a high degree of linearity of the transformer over the entire transmission range, with, at the same time, minimum manufacturing costs. These two requirements are, however, difficult to fulfil simultaneously. In practice, the actual properties of a transformer therefore derive from a compromise, which is to be decided on according to the particular application situation.
An additional problem is incurred by the bandwidth of the transformer. In many applications, a large bandwidth is required. In conjunction with high linearity, however, this is associated with higher costs. Accordingly, with the use of a transformer, the problem arises of optimisation of the parameters of bandwidth, linearity, and manufacturing costs. Inasmuch as no compromises are possible with the bandwidth or the linearity, the comparatively high costs for the transformer, incurred in particular due to its core material as well as by its mechanical layout, were hitherto unavoidable.
Reductions are possible with regard to the bandwidth, but these are not optimum. With SHDSL systems (“Single-Pair-High-Bit-Rate Digital Subscriber Line”), the required bandwidth of the transformer is, for example, proportional to the variable signal bandwidth of the system or the transceiver. The optimum lower limit frequency of the transformer for a maximum data rate or range width of the system is approximately proportional to the bandwidth of the system. While too low a lower limit frequency of the system can be adjusted by means of a digital highpass filter in increments to the signal bandwidth of the system, i.e. can be increased, a lower limit frequency which is too high cannot be compensated for subsequently. Efforts must therefore be made to arrange the lower limit frequency of the transformer to suit the smallest bandwidth of the system which is to be used, and the upper limit frequency of the transformer to correspond to the greatest bandwidth which is to be used. If this is not possible, a compromise which frequently satisfies is to lay out the transformer only for the largest bandwidth to be used, whereby reductions in the performance at the smallest bandwidths to be used are taken into account.
With xDSL systems, in general a substantial linearity of the transformer for a maximum data rate or range is in most cases only required on such channels as have only low crosstalk, or none at all. The use of xDSL systems is in many cases subject to strictly formulated rules (known as “Deployment Rules”), which are intended to ensure functional performance even with the greatest fault incidence to be assumed (“worst case”). Accordingly, if a system is only designed for the greatest fault incidence to be assumed, such as, for example, the presence of severe cross-talk interference, the requirements for linearity are reduced, because the interference caused by the non-linearity in the presence of interference caused by cross-talk noise does not occur. A transformer designed in this way is in this case not well-suited for transmission on channels with low cross-talk.
A further possibility consists of offering different equipment fitting variants on a line card, for example, with in each case a transformer for specific applications. A disadvantage of this procedure is, inter alia, the additional re-equipping with components required in addition to the transformer, since the dimensions of the circuit as a whole is frequently dependent on the properties of the transformer used in each individual case. In addition to this, extensive test series are in most cases required for such systems, which are incurred anew for each circuit variant.
The re-equipping of components referred to, however, excludes a desirable switchover in terms of software between different operational frequency ranges or transformers, with the result that only one electronic or electromechanical switchover comes into consideration. The use of electronic switches is problematic, however, since highly linear electronic switches are necessary because of the high demands for linearity, which are associated with high costs. In addition, switchover by means of relays is also possible. This, however, represents an additional component to be accommodated on a line card per channel, so that less space remains for the equipping of as many channels as possible.
The object of the invention is to provide an economical transformer circuit arrangement with which signals can be transmitted with a large frequency bandwidth and with high linearity.
This object is achieved by a transformer circuit arrangement according to claim
1
. Subclaims refer to preferred embodiments.
The transformer circuit arrangement according to the invention has a first transformer with at least two inputs or input connections respectively, and two outputs or output connections respectively, and a first frequency response with a first lower limit frequency and a first upper limit frequency, as well as a second transformer with at least two inputs or input connections respectively, and two outputs or output connections respectively, and a second frequency response with a second lower limit frequency and a second upper limit frequency. The first lower limit frequency is smaller than the second lower limit frequency, and the second upper limit frequency is greater than the first upper limit frequency. In addition, the second lower limit frequency is preferably not greater or smaller by a factor of 10 than the first upper limit frequency. The transformer circuit arrangement according to the invention has a frequency behaviour with bandpass character with a lower overall limit frequency and an upper overall limit frequency. In this situation, the lower overall limit frequency is smaller than the first upper limit frequency of the first transformer and the second lower limit frequency of the second transformer, and the upper overall limit frequency is greater than the second lower limit frequency of the second transformer and the first upper limit frequency of the first transformer.
The first and/or the second transformer can have an individual transformation ratio in each case, an individual main inductance, and an individual scatter inductance. Advantageously, the transformation ratio of the first transformer is equal to the transformation ratio of the second transformer. As a result, the transformers can be arranged symmetrically to one another in respect of their frequency response.
The first and second transformers can be designed as quadripole units with in each case two inputs and two outputs. The inputs of the transformers can be connected together in parallel or series. Likewise, the outputs of the transformers can be connected in parallel or series. According to one advantageous embodiment, either the inputs are connected in parallel and the outputs as series, or the inputs as series and the outputs in parallel. As a result of this, an addition of the frequency responses of the individual transformers can be achieved, to form one overall total frequency

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