Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Phase shift by less than period of input
Reexamination Certificate
2000-05-30
2001-10-30
Wells, Kenneth B. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Phase shift by less than period of input
C327S244000, C327S248000
Reexamination Certificate
active
06310502
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention is directed to a broadband phase shifter circuit.
More specifically, the invention is directed to a broadband phase shifter circuit, particularly for an IQ modulator, comprising two phase shifter branches connected parallel to which the input signal to be shifted in phase is supplied at the input side and that supply phase-shifted output signals at their outputs shifted by a predetermined angle, such as 90°.
Broadband phase shifter circuits of this species are known; for example, they are employed as 90° phase shifters for IQ modulators (for example, according to U. S. Pat. Nos. 4,908,532, 4, 951,000 or 5,644,260). However, these respectively have various disadvantages. The fashioning of the phase shifters as RC elements with variable capacitance diodes and their regulation via a phase detector connected between the outputs (U.S. Pat. No. 4,908,532) results in indefinite amplitudes of the output voltages at the two phase shifter branches. The different amplitudes deteriorate the modulation precision of the following IQ modulator. The opposed phase correction of two identical phase shifters in the two phase shifter branches via a phase detector (U.S. Pat. No. 4,951,000) is limited to specific phase shifters and cannot be employed, for example, given simple RC elements. The regulation of the two phase shifter branches dependent on the difference of the amplitude of the two output voltages (U.S. Pat No. 5,644,260) is not exact enough with respect to adhering to the desired, exact phase relationship.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to create a broadband phase shifter circuit that avoids these disadvantages and assures exact adherence to the desired phase angle, given amplitudes of the output voltages of respectively the same size in a broad frequency range regardless of the kind of phase shifters employed.
To that end, in an embodiment the invention provides a phase shifter circuit in which the phase shifter of the one phase shifter branch is controlled dependent on the frequency (f) of the input signal such that the phase angle between the two output signals approximately corresponds to the desired value (rough control); and the phase shifter of the other phase shifter branch is regulated to the desired phase angle via a phase detector connected between the outputs of the two phase shifter branches (fine control).
In an embodiment, the invention provides a broadband phase shifter circuit, comprising: two phase shifter branches connected in parallel to which an input signal to be shifted in phase is supplied at a common input side and which supply at respective outputs phase-shifted output signals shifted by a predetermined angle, wherein, each phase shifter branch comprises a phase shifter, the phase shifter of one phase shifter branch is controlled dependent on the frequency of the input signal such that the phase angle between the phase-shifted two output signals approximately corresponds to a desired value for relatively rough control purposes, the phase shifter of the other phase shifter branch is controlled to the desired phase angle via a phase detector connected between the outputs of the two phase shifter branches for relatively fine control purposes.
In an embodiment of the invention, the phase shifter of the one phase shifter branch comprises an RC low-pass element and the phase-shifter of the other phase-shifter branch comprises an RC high-pass element.
In an embodiment of the invention, the phase shifters in the phase shifter branches comprise all-pass filters.
In an embodiment of the invention, there are included respective variable resistors for effecting the rough control and fine control.
In an embodiment of the invention, the variable resistors comprise drain-source paths of field effect transistors.
In an embodiment of the invention, there is included respective variable capacitances for effecting the rough control and fine control.
In an embodiment of the invention, there is included the phase shifters of the two phase shifter branches comprise RL elements with variable resistors.
In an embodiment of the invention, the phase shifters of the two phase shifter branches comprise RL elements with variable resistors and variable inductances.
In an embodiment of the invention, the actuating variables belonging to the respective frequency for the rough control are stored in a memory and are read therefrom dependent upon the frequency of the input signal.
In the inventive phase shifter circuit, one phase shifter branch, dependent on the frequency of the input signal, is roughly set to a value that approximately corresponds to the desired, predetermined phase angle. Only the second phase shifter branch is re-adjusted so finely via a phase detector that the desired, predetermined phase angle, for example 90°, is ultimately achieved. This principle of rough pre-setting and fine readjustment is suitable for all possible phase shifters, both for simple RC elements as well as for all-pass elements, delay elements or phase shifter circuits upon employment of inductances as well. The only pre-condition is that the phase shifters employed can be respectively dimensioned such in the two phase shifter branches that the output signals at their two outputs respectively exhibit the desired phase angle. Since, according to the invention, fine regulation is undertaken via the phase detector directly dependent on the phase and not via the expedient of an amplitude comparison, the circuit is also insensitive to temperature effects and aging of the components. As a result of the combined rough control / fine adjustment, preferably via variable resistors in the phase shifters of the branches, an inventive phase shifter circuit is extremely broadband over up to two frequency decades.
The invention is explained in greater detail below on the basis of schematic drawings with reference to an exemplary embodiment.
These and other features and aspects of the invention will become clear in the following detailed description of a few typical exemplary embodiments with reference to the accompanying drawings.
REFERENCES:
patent: 4558291 (1985-12-01), Nichols
patent: 4908532 (1990-03-01), Chadwick
patent: 4951000 (1990-08-01), Dautriche
patent: 5101117 (1992-03-01), Johnson et al.
patent: 5124656 (1992-06-01), Yassa et al.
patent: 5631591 (1997-05-01), Bar-Niv
patent: 5644260 (1997-07-01), DaSilva et al.
patent: 44 20 376 A (1995-03-01), None
patent: 0 645 885 A1 (1995-03-01), None
Rohde & Schwarz GmbH & Co. KG
Schiff & Hardin & Waite
Wells Kenneth B.
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