Patent Application
20090079882
The present invention relates generally to communication devices or receivers. More specifically, the present invention relates to a mobile receiver suitable for analog TV signal decoding using digital tuner with the associated I, Q output.
Separated analog tuner and digital tuner are known to be combined for use in receiving and displaying there respective signals. United States Patent Application No. 20070083903 to Wan el al describes an Audio/video system for a notebook computer.
Converting both analog television signal and digital television signal to an intermediate frequency signal for subsequent processing is known. U.S. Pat. No. 7,265,792 to Favrat, et al. describes a Television receiver for digital and analog television signals in which a television receiver includes a frequency conversion circuit, an analog-to-digital converter, a signal processor, and a signal output circuit. The frequency conversion circuit receives an input RF signal in one of several television signal formats and converts the input RF signal to an intermediate frequency signal. The analog-to-digital converter samples the intermediate frequency signal and generates a digital representation thereof. The signal processor processes the digital representation of the intermediate frequency signal in accordance with the television signal format of the input RF signal and generates digital output signals indicative of information encoded in the input RF signal. Finally, the signal output circuit receives the digital output signals from the signal processor and provides one or more output signals corresponding to the digital output signals. The signal output circuit can be configured to provide output signals corresponding to an analog television format or a digital television format or both.
The digital TV (DTV) and other digital communication systems make use of I (In-phase) and Q (Quatrature) components to represent and decode the full digital single side band signals. The Radio Frequency Integrated Circuit (RFIC), or tuner changes the incoming signal frequency, from typically several million mega HZ, into base-band, i.e. centered at zero HZ. For the spectral side band signal such as digitally modulated signals, I and Q components must be used.
For the analog signals, they are typically modulated using Vestigial Side-Band (VSB) methods with some residual spectral components in the other side of signal modulation frequency. The prior methods all decode the analog video signals using a single component. The complex I and Q representation may not be needed from theoretical point of view to decode the signals. But such representation can be easily used to correct the center frequency offset, simplify the tuner design and to improve the signal noise ratio (SNR).
Currently a lot of countries are transitioning from analog television signal to digital television signal. During the transition, both analog television signal and digital television signal may co-exist. Even after the transition analog signal still may exist for various purposes. Therefore, a digital television (DTV) receiver that can process analog television signal is desirable and sometime mandatory.
A method for producing a television receiver comprising the step of providing a digital tuner for processing analog signals to its respective I and Q components is provided.
A dual use TV receiver for both analog TV and DTV using a digital tuner for processing analog signals and converting same to its respective I and Q components is provided.
The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
Before describing in detail embodiments that are in accordance with the present invention, it should be observed that the embodiments reside primarily in combinations of method steps and apparatus components related to a method for producing a television receiver comprising the step of providing a digital tuner for processing analog signals to its respective I and Q components. Accordingly, the apparatus components and method steps have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.
In this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.
It will be appreciated that embodiments of the invention described herein may be comprised of one or more conventional processors and unique stored program instructions that control the one or more processors to implement, in conjunction with certain non-processor circuits, some, most, or all of the functions of relating to a method for producing a television receiver comprising the step of providing a digital tuner for processing analog signals to its respective I and Q components. In the exemplified embodiments, it is noted that the processors include Finite State Machines, which are used in the preferred embodiment. The non-processor circuits may include, but are not limited to, a radio receiver, a radio transmitter, signal drivers, clock circuits, power source circuits, and user input devices. As such, these functions may be interpreted as steps of a method with reduced memory requirements to perform a method for producing a television receiver comprising the step of providing a digital tuner for processing analog signals to its respective I and Q components. Alternatively, some or all functions could be implemented by a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in which each function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the two approaches could be used. Thus, methods and means for these functions have been described herein. Further, it is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such software instructions and programs and ICs with minimal experimentation.
This invention makes use of I and Q components to decode the analog TV signals. A set of dedicated filters are employed to reduce multi-path interference and enhance the signal to noise ratio (SNR) of the video signals as well as the audio signals.
Compared to pure DTV processing, when analog signals' respective I and Q components are converted into video signal's zero HZ and extracted, the higher frequency portion is not same as pure digital ones where the lower frequency portion is the same and somewhat redundant because of the VSB (Vestigial Single Band) modulations. The adjacent channel signals can be leaked into the signal. If the real centered frequency rather than the VSB signal's nominal central frequency is used to down-convert the signal, the above mentioned problems can be alleviated, but I and Q representation must be used.
The first step is to use the zero-IF, or the near-zero IF, architecture down-converter to convert the RF frequency signal into the base-band with I and Q components. After the low-pass filtering, the signals are converted into the digital domain. Then the signals splits into two paths (not shown), one is for the video. It is rotated into the base-band centered according the VSB modulations. Then it is filtered using match filter and equalizer to minimize the effects of multi-path and audio signals.
The other path (also not shown) is for the audio. The signal is again down-converted into the audio center frequency and filtered again. An FM decoding is performed similar to the extraction of the stereo audio signals like FM and others.
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The processing bandwidth of the present invention is half of the received analog signal and makes the implementation of same easier and more cost effective. Further, for analog TV such distortion is not acceptable. So some DC restoration circuit must apply. In addition, the I and Q components make the frequency control operations easy as compared to pure analog or partial analog systems.
The present invention filters out some unwanted spectrum using some I and Q signal components in that the unwanted signal, which is not symmetric to the zero frequency is filtered. Also some dc restoration is performed for recovering some zero-frequency component.
In the foregoing specification, specific embodiments of the present invention have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.
