Television – Television transmitter circuitry
Reexamination Certificate
1998-01-26
2001-10-16
Harvey, David E. (Department: 2714)
Television
Television transmitter circuitry
C348S725000, C348S572000
Reexamination Certificate
active
06304301
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for preparing a band pass signal and, in particular, to a method for preparing an analog band pass signal received from an intermediate frequency position for various transmission conditions.
German patent document DE 40 26 477 A1 discloses a method for forming a frequency multiplex signal (FDM) with digital signal processing, such as an analog band pass signal, which is preferably a modulated TV signal which can be displayed, received, and processed in a intermediate frequency position. The received band pass signal is converted via an analog/digital converter into a digital band pass signal and further converted for further processing into a corresponding digitally filtered and frequency adjusted condition. Several such types of prepared digital band pass signals are converted into the frequency in a manner such that they are coupled with one another in a frequency domain in an overlapping free manner and are combined into a frequency multiplex signal through digital addition. For a selected or predetermined receipt frequency, the middle frequency of the band pass signals must be set and maintained in a narrow tolerance range since the receipt frequency is chosen as the minimum reliable value in accordance with signal receipt theory. As a result, the processing rate in the digital frequency conversion apparatus is relatively low; in contrast, however, the total work in the realization of this processing rate is relatively high due to the small transfer region of the analog pre filter (especially an anti-alias filter) and the digital filter. In a further configuration of this processing rate as disclosed in German patent document DE 43 37 134 A1, a doubled sampling frequency is processed and this leads to the following advantages: —all of the filter demands are eliminated (analog and digital), -the neighboring channel selection (the immediately neighboring channel) does not need to be implemented via the tolerance restricted analog anti-alias filter but, rather, via a robust digital deep pass filter, —the band middle frequency of the band pass signal to be processed is the same as a standard intermediate frequency position such as, for example, a European norm with the image carrier of 38.9 Hz, and even cost favorable standard ZF filters can be used as the anti-alias filter in advance of the analog/digital conversion.
SUMMARY OF THE INVENTION
The present invention advantageously provides, in one aspect of the method thereof, the ability to use integral or identical digital signal preparation units of different transmission norms. The conformation to the respective standard can be substantially effectuated with software-namely, through the provision of different filter coefficients and mixing frequencies. Additionally, the method of the present invention avoids the need to provide a specific digital filter or frequency conversion apparatus for each television norm.
The method of the present invention also permits the use of simple digital filters with relatively high tolerance demands. In accordance with one aspect of the method of the present invention, a real value analog band pass signal is converted into a real digital band pass signal. A transfer of the signal into a complex signal, always in digital form, is eventually effectuated via the analog/digital conversion. Thus, the typical parallel processing and tolerance problems of analog processing rate of complex signals is basically avoided.
REFERENCES:
patent: 40 26 477 A1 (1992-03-01), None
patent: 4136111 (1993-05-01), None
patent: 43 37 134 A1 (1995-05-01), None
Harvey David E.
Robert & Bosch GmbH
Striker Michael J.
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