Amplifiers – Hum or noise or distortion bucking introduced into signal...
Reexamination Certificate
1999-10-06
2001-05-29
Lee, Benny (Department: 2817)
Amplifiers
Hum or noise or distortion bucking introduced into signal...
C375S297000, C455S126000
Reexamination Certificate
active
06239657
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for measuring the distortion of a high-frequency power amplifier and to a corresponding measuring device. The invention also relates to an equalizing method for automatically equalizing a high-frequency power amplifier and to a corresponding equalizing means.
High-frequency power amplifiers usually do not have an entirely linear characteristic. This causes a distortion of the high-frequency signal that is amplified by the high-frequency power amplifier. Thus, due to the non-linearities of the high-frequency power amplifier, an undesirable noise spectrum emerges.
Given multi-carrier signals such as are used in the digital transmission of audio and video signals, the noise spectrum is expressed in extraband disturbances, which lie outside the transmission band, and intraband disturbances, which lie inside the transmission band. To guarantee a perfect transmission of the multi-carrier signal, the noise spectrum must comprise a predetermined level distance from the useful signal. Therefore, relatively high requirements are set for the linearity of high-frequency power amplifiers in the output stage of an amplifier for DAB (Digital Audio Broadcasting) signals and DVB (Digital Video Broadcasting) signals.
Previously, in the balancing of high-frequency power amplifiers of this type, it was common to feed a multi-carrier balancing signal to the input and to observe the output signal of the high-frequency power amplifier with a spectrum analyzer. In the signal path prior to the high-frequency power amplifier, a predistorting means was arranged, which permits a predistorting of the high-frequency signal that is to be amplified. The predistortion characteristic is defined by a diode resistance network with variable resistances, so that the curve of the predistortion characteristic can be variably adjusted by a plurality of parameters. By varying the adjustment parameters of the predistortion network, it was then iteratively attempted to achieve an optimally large shoulder spacing between the useful signal and the noise signal in the output spectrum of the high-frequency power amplifier. Since there is no strategy for adjusting the individual parameters of the predistortion network, and the adjustments of the individual parameters have a mutual influence on one another, this procedure is extremely time-consuming and thus expensive. Furthermore, an adjustment that has been found is dependent on the temperature, the age of the components of the high-frequency power amplifier, and other influences.
SUMMARY OF THE INVENTION
It is thus an object of the present invention to provide a suitable measuring method for measuring the distortion of a high-frequency power amplifier and a suitable method for automatically equalizing a high-frequency power amplifier, as well as a corresponding measuring means and a corresponding equalizing means.
To that end, in an embodiment, the invention provides a method of measuring the distortion of a high-frequency power amplifier comprising the following steps:
a) measuring an input signal and an appertaining output signal of the high-frequency power amplifier;
b) separating the input signal of the high-frequency power amplifier into an input envelope curve and a reference carrier;
c) generating an output envelope curve of the output signal of the high-frequency amplifier with the aid of the reference carrier that is generated from the input signal; and
d) displaying a control characteristic of the high-frequency power amplifier in the form of the amplitude or the power of the output envelope curve as a function of the amplitude or power of the input envelope curve.
In an embodiment, the invention provides an apparatus which measures the distortion of a high-frequency power amplifier, comprising:
a) a reference carrier generator which generates a reference carrier from a measured input signal of the high-frequency power amplifier;
b) a first synchronous demodulator which generates an input envelope curve from the measured input signal and the reference carrier;
c) a second synchronous demodulator which generates an in-phase component of an output envelope curve from the measured output signal of the high-frequency power amplifier and from the reference carrier;
d) a phase shifter which shifts the phase of the reference carrier 90°;
e) a third synchronous demodulator which generates a quadrature component of the output envelope curve from the measured output signal of the high-frequency power amplifier and from the reference carrier, which has been shifted 90° in phase;
f) a first display which displays a control characteristic of the high-frequency power amplifier in the form of the amplitude or power of the output envelope curve as a function of the amplitude or power of the input envelope curve; and
g) a second display which displays a phase characteristic of the high-frequency power amplifier in the form of the phase angle of the output signal, which is defined by the ratio of the quadrature component to the in-phase component, as a function of the amplitude or power of the input envelope curve or as a function of the amplitude or power of the output envelope curve.
In an embodiment, the invention provides an equalization apparatus which automatically equalizes a high-frequency power amplifier, comprising:
a) a reference carrier generator which generates a reference carrier from a measured balancing input signal of the high-frequency power amplifier;
b) a first synchronous demodulator which generates an input envelope curve from the measured balancing input signal and from the reference carrier;
c) a second synchronous demodulator which generates an in-phase component of an output envelope curve from a measured balancing output signal of the high-frequency power amplifier and from the reference carrier;
d) a phase shifter which shifts the phase of the reference carrier 90°;
e) a third synchronous demodulator which generates a quadrature component of the output envelope curve from the measured output signal of the high-frequency power amplifier and from the reference carrier, which has been shifted 90° in phase;
f) a controller which generates an amplitude correction control signal and/or a phase correction control signal from the input envelope curve, the in-phase component of the output envelope curve and/or the quadrature component of the output envelope curve; and
g) a signal predistorter means, whose control characteristic and phase characteristic are adjusted in the balancing mode inversely to the control characteristic and/or the phase characteristic of the high-frequency power amplifier, by the amplitude correction factor and/or by the phase correction factor;
wherein,
the control characteristic is defined by the amplitude or power of the output envelope curve as a function of the amplitude or power of the input envelope curve, and
the phase characteristic is defined by the phase angle of the output signal as a function of the amplitude or power of the input envelope curve or as a function of the amplitude or power of the output envelope curve.
The inventive measuring method has the advantage that the control characteristic of the high-frequency power amplifier is directly indicated. The operator thus has an effective balancing criterion in the balancing of the high-frequency power amplifier, or respectively, of a predistorting means arranged in front of the high-frequency power amplifier; namely, to achieve an optimally extensive linearizing of the control characteristic.
The generation of the output envelope curve and the input envelope curve advantageously occurs by means of synchronous demodulation. To indicate the phase angle, both an in-phase component and a quadrature component are generated by the output envelope curve. The phase angle of the output signal can be determined from the ratio of these two components. The synchronous demodulation of the in-phase component and the quadrature component advantageously occurs in separate synchronous demodulators. In addition, the reference car
Lee Benny
Nguyen Khanh Van
Rohde & Schwarz GmbH & Co. KG
Schiff & Hardin & Waite
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