Pulse or digital communications – Receivers – Interference or noise reduction
Reexamination Certificate
1998-06-22
2001-03-27
Chin, Stephen (Department: 2734)
Pulse or digital communications
Receivers
Interference or noise reduction
C375S217000, C375S324000, C375S316000
Reexamination Certificate
active
06208700
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an apparatus for processing a signal received via an information carrier, which apparatus comprises in succession a receiving unit for receiving the signal, an equalizer and a signal processing device.
An apparatus of the type defined in the opening paragraph is known from U.S. Pat. No. 4,905,102. The known apparatus reads a signal from an information carrier by means of a receiving unit. The signal thus obtained is subsequently applied to an equalizer and a signal-processing device. The known signal processing device includes a circuit for improving the applied signal. It has been found that the known signal processing device does not effectively suppress some disturbances in the signal.
SUMMARY OF THE INVENTION
It is an object of the invention to improve the signal by reducing the influence of inter-symbol interference, such as low-frequency noise and variations of the average signal value (baseline wander), on the zero crossings in the signals. To this end, the signal processing device is characterized in that the signal processing device includes:
a first and a second signal path each having an input and an output, the first and the second signal path having their inputs coupled to an input of the signal processing device,
the first signal path including time delay means,
the second signal path including differentiation means adapted to effect at least two differentiations with respect to time,
a controllable switching element having a first and a second signal input, which first signal input is coupled to the output of the first signal path and which second signal input is coupled to the output of the second signal path, a control signal input arranged to receive a control signal for setting the controllable switching element to a first state or a second state, and a signal output coupled to the first signal input in the first state and coupled to the second signal input in the second state,
a decision circuit having a first and a second input, which first input is coupled to the output of the first signal path and which second input is coupled to the output of the second signal path, and having an output coupled to the control input of the controllable switching element to transfer a control signal, the decision circuit being adapted to supply the control signal in dependence upon the signals applied to the first and the second input.
The apparatus in accordance with the invention operates as follows: In the apparatus a signal is read from an information carrier by means of a receiving unit. After this, the signal is equalized by an equalizer. However, the signal from the equalizer still contains disturbances as a result of which a bit detector which may have been coupled sometimes cannot detect the zero crossings in the original non-disturbed signal or detects them at the wrong instants. The signal from the equalizer is subsequently applied to the two signal paths of the signal processing device. In one path the signal is differentiated at least two times. As a result of this, peaks in the applied signal become more distinct. In the other path the signal from the equalizer is delayed by a time which substantially corresponds to the time delay introduced by the differentiation means. As a result of this, the signals reach the outputs of the first and the second signal path at substantially the same time. The decision circuit generates a control signal on the basis of the signals on the outputs of the first and the second signal path. The controllable switching element transfers the signal on the output of the first or the second signal path on the basis of the value of the control signal. As a result of this, the zero crossings in the signal become more distinct. The invention is suitable for an apparatus as mentioned in U.S. Pat. No. 4,905,102. However, it can be used in any apparatus in which an applied signal is disturbed by inter-symbol interference, such as TV equipment and mobile telephones.
An embodiment of the apparatus is characterized in that the decision circuit further includes comparison means for comparing the amplitudes of the signals applied to the first and the second input. In this embodiment the control signal indicates which of the signals on the two inputs has the larger amplitude.
A further embodiment of the apparatus is characterized in that the input of the signal processing device is adapted to transfer a sampled digital signal and the time delay means are adapted to delay the sampled digital signal by a time which is substantially equal to the time delay introduced by the differentiation means. The time delay means then ensure that time-equivalent samples are applied simultaneously to the decision circuit and the controllable switching element.
It is to be noted that from U.S. Pat. No. 3,252,098 an apparatus is known which includes a signal processing device comprising time delay means and a circuit for effecting two differentiations with respect to time. However, said apparatus neither includes an equalizer nor comparison means and switching means.
REFERENCES:
patent: 3252098 (1966-05-01), Schlaepfer
patent: 4528678 (1985-07-01), Udren
patent: 4837624 (1989-06-01), Heitmann et al.
patent: 4905102 (1990-02-01), Schulz
patent: 5638407 (1997-06-01), Hatanaka et al.
patent: 5659576 (1997-08-01), Critchlow et al.
patent: 0084358 (1990-07-01), None
Biren Steven R.
Chin Stephen
Ghayour Mohammad
U.S. Philips Corporation
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