The present invention relates to an arrangement for recovering a digital signal from a digital input signal, a receiver and a radio comprising such an arrangement. The invention further relates to a computer-programming product for recovering a digital signal from a digital input signal.
The present invention can be used in receivers, such as a radio receiver or a video/TV receiver for recovering e.g. a pilot signal, a center frequency signal or a color burst signal. These kinds of receivers are generally known in the art and typically make use of a phase locked loop to lock onto the frequency of the recoverable signal. In general, however, phase locked loops are difficult to design and are sometimes even impractical. For example, when the phase of the recoverable signal is not a constant value but changes due to poor receiving conditions or when the recoverable signal is severely degraded by the presence of noise. In these cases, the phase locked loop might not be able to track the phase of the signal, which causes an erroneous frequency lock.
It is an object according to the present invention to provide an arrangement for recovering a signal without using a phase locked loop. To this end the arrangement for recovering a first digital signal from a digital input signal, comprises:
The invention is based upon the insight that the first digital signal can be recovered by determining the phase difference between an arbitrary but well-defined reference signal and the recoverable signal, followed by an addition of the phase difference to the phase of the reference signal.
An arrangement for recovering a signal without a phase locked loop is known from U.S. Pat. No. 5,404,405 but an alternative solution is provided there in which the signal is recovered by means a FIR (Finite Impulse Response) filter which has a complex implementation particularly with a narrow passband.
In an embodiment of the arrangement according to the present invention an offset value is added to the phase of the recovered first digital signal for compensating a filter delay of the digital filter. Herewith, the distortive effect of filter delay that may cause a phase error in the recovered signal can be corrected.
In another embodiment of the arrangement according to the present invention the arrangement comprises a first digital mixer for frequency down-converting the digital input signal before filtering. This embodiment has the advantage of a less complex implementation of the digital filter.
In an embodiment of the arrangement according to the present invention the digital input signal is a stereo multiplex signal and the recovered first digital signal is a pilot signal. Herewith, the arrangement can be used to recover a pilot signal in a convenient way.
In an embodiment of the arrangement according to the present invention a phase of a pilot signal is multiplied by a multiplier for recovering a second digital signal. By multiplying the phase of the (19 kHz) pilot by a multiplier, other (sub)carriers such as, the 38 kHz suppressed carrier signal, the 57 kHz RDS sub carrier or the 76 kHz DARC sub carrier can easily be recovered.
In another embodiment of the arrangement according to the present invention the arrangement further comprises a stereo decoder for decoding the stereo multiplex signal into at least a first and a second signal. Herewith, the left and right stereo channels, which are coded in received stereo multiplex signal, can conveniently be decoded.
In an embodiment of the arrangement according to the present invention, the stereo multiplex signal comprises a sum signal and a difference signal, the former signal being decoded by adding the sum signal to a frequency down-converted difference signal, the latter signal being decoded by subtracting the frequency down-converted difference signal from the sum signal.
In an embodiment of an arrangement according to the present invention the difference signal is frequency down-converted by means of the recovered suppressed carrier signal. Since the suppressed carrier signal is directly derived from the recovered pilot signal it has the correct frequency and phase to shift the difference signal of the stereo multiplex signal to baseband.
In another embodiment of the arrangement according to the present invention the phase offset value is further arranged to control the amplitude of the difference signal. Herewith, it is possible to manipulate the decoded first and second signals for example, from mono to stereo signals.
Embodiments of a receiver, a radio and a computer programming product according to the present invention, correspond with the embodiments of the arrangement according to the present invention.
These and other aspect of the present invention will be elucidated further by means of the following drawings.
The left stereo channel L is obtained by adding together in the adder 56 the sum signal 1, 59 and the difference signal 3, 59. The right stereo channel R is obtained by subtracting in subtracter 54 the difference signal 3, 57 from the sum signal 1,59. The difference signal 3 is obtained from the stereo multiplex signal 20 by frequency down converting 50 and low-pass filtering 52 the stereo multiplex signal 20. The stereo multiplex signal 20 can be frequency down converted by means of a conventional (digital) mixer 50 that uses the recovered suppressed carrier signal 9, 32 as a mixing signal.
Phase offset signal 23 is used to compensate the phase distortion which may be introduced into the recovered pilot signal 31 by the filter delay of filter 29. However, this phase offset signal can also be used to manipulate the phase of suppressed carrier signal 9,32. Herewith the amplitude of difference signal 57 can be influenced which in turn influences the recoverable left (L) and right (R) channels. For example, from stereo channels to mono channels.
It is to be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. The embodiments can be realized either in hardware or in software. The word “comprising” does not exclude the presence of elements or steps other than those listed in a claim. The word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.
Number | Date | Country | Kind |
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03102241.1 | Jul 2003 | EP | regional |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB04/51240 | 7/16/2004 | WO | 1/17/2006 |