Electrical computers and digital data processing systems: input/ – Input/output data processing – Peripheral adapting
Reexamination Certificate
1998-09-29
2001-07-10
Lee, Thomas (Department: 2182)
Electrical computers and digital data processing systems: input/
Input/output data processing
Peripheral adapting
C710S065000, C710S120000, C710S062000, C360S023000, C360S032000, C360S060000, C341S108000, C341S120000
Reexamination Certificate
active
06260085
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a changeover device which uses both analog and digital signals as input signals and supplies an analog output signal.
Such a changeover device can be used wherever an analog output signal has to be available for further processing and the analog output signal can be obtained both from a digital input signal and from an analog input signal.
In television technology, analog and digital signals are often processed at the same time. The video signal which is broadcast by the television stations for the purpose of television picture transmission, is converted into the baseband in a television receiver and is present as a color, video, blanking, syncs signal (CVBS), has an analog nature. If the picture information of the CVBS signal is intended to be processed further, it is frequently converted into a digital video signal in order to utilize the advantages of digital signal processing. Picture-in-picture insertions constitute an example of this. The analog picture information of an additional picture which is intended to be inserted into a main picture as a picture that is reduced in size is processed after analog-to-digital conversion. The processing of the digital video signal may serve for example for matching the format of the additional picture to the main picture. After processing, the digital video signal is converted back into an analog video signal, from which RGB signals are generated which can be fed to a picture tube.
The amplitude of the RGB signals should be independent of whether they are obtained directly from an analog signal or from an analog signal after analog-to-digital conversion and subsequent digital-to-analog conversion.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a changeover device for analog and digital signals, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which generates from both analog and digital input signals an analog output signal the amplitude of which is independent of whether it is obtained from the analog or the digital input signal.
With the foregoing and other objects in view there is provided, in accordance with the invention, a changeover device, comprising:
a digital signal input for receiving a digital input signal, an analog signal input for receiving an analog input signal, and an output for outputting an analog output signal;
a digital-to-analog converter connected to the digital signal input;
a driver driving the output of the changeover device and having an input;
the digital-to-analog converter having a voltage divider connected between a reference-ground voltage and the driver, wherein a division ratio can be set in dependence on the digital input signal and a part of the reference-ground voltage determined by the division ratio can be fed to the input of the driver; and
a switch connected between the analog signal input and the input of the driver for selectively supplying the analog input signal to the driver.
In other words, the objects of the invention are satisfied by a changeover device having inputs for a digital input signal and an analog input signal and having an output for an analog output signal, and also having a digital-to-analog converter, which has a voltage divider between a driver and a reference-ground voltage, whose division ratio can be set in dependence on the digital input signals, and via which a part of the reference-ground voltage, which part is determined by the division ratio, can be fed to an input of the driver, the input for the analog input signal being connected via a first switch to the input of the driver and the driver supplying the analog output signal on the output side.
The invention has the advantage that it manages with just one driver for the analog and the digital input signal. A further advantage of the changeover device according to the invention is the fact that analog input signals having different levels can be used.
In accordance with an added feature of the invention, a second switch and a limiting resistor are connected between the analog signal input and the voltage divider.
In accordance with an additional feature of the invention, the voltage divider contains a series circuit of resistors.
The second switch is closed when a CVBS signal is clamped at an input quiescent level in the event of using a video signal as analog input signal.
In accordance with another feature of the invention, a further digital-to-analog converter supplies the reference-ground voltage. The further digital-to-analog converter is connected to a reference voltage and is adapted to adjust the reference-ground voltage in steps.
In accordance with a further feature of the invention, the further digital-to-analog converter contains at least three series-connected converter resistors and at least one switch series comprising selector switches, the selector switches each being connected to one another on one side and between two converter resistors, respectively, on the other side.
In accordance with again another feature of the invention, the at least one switch series are three switch series.
In accordance with a concomitant feature of the invention, the digital input signal is a digital video signal for generating a main picture and the analog input signal is an analog video signal for an additional picture selectively insertable into the main picture.
Furthermore, the reference-ground voltage is preferably adjusted by means of a further digital-to-analog converter. That voltage can be altered in the course of operation.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a changeover device for analog and digital signals, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
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Greenberg Laurence A.
Infineon - Technologies AG
Lee Thomas
Lerner Herbert L.
Schuster Katharina
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