Method and device for comparing two variable analogue signals

Details Method and device for comparing two variable analogue signals Method and device for comparing two variable analogue signals

1991-09-10

1994-04-19

Nguyen, Long T.

Boots, shoes, and leggings

G06J 100

Patent

active

053052439

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of The Invention
The invention concerns a method and device for comparing two variable analogue signals, e.g. varying in time, such as audio or video signals, these signals being either different or identical but shifted in time.
2. Description of Related Art
To compare two variable analogue signals, a correlation function must be determined between these signals and the values of this function used to verify whether or not identity exists between the signals.
The correlation function is determined by numerical computation methods and implies use of sharp cut-off bandpass filters, analogue-to-digital converters, a system for processing information allowing real-time computation of the correlation function; and a complex processing algorithm capable of identifying and compensating for any shift between the two signals. Systems designed to perform this computation are generally fairly expensive.
Other various devices are used that measure the phase shift between two sine-wave analogue signals of the same frequency. However, these devices cannot be used for signals that are not purely sine-wave, such as audio or video signals received or produced by radio and television receivers.


SUMMARY OF THE INVENTION

The main objective of the invention is to simplify the above-mentioned numerical computation methods and systems, thereby significantly reducing their cost while retaining the desired speed and accuracy for establishing the correlation.
Another objective of the invention is to provide a correlation measurement between two analogue signals of the above-mentioned type, but which does not require a time or phase measurement.
For this purpose, the invention provides a method for comparing two variable analogue signals that consists in establishing a correlation signal between the analogue signals, and in using the values of this signal to verify whether or not identity exists between the analogue signals. The signals to be compared are either identical but shifted in time, or different, and cover a predetermined frequency range, it consists in:
transforming the said analogue signals into binary logic signals in order to present these binary signals to the inputs of an exclusive OR or multiplier type logic circuit (32), and then implementing a summing function on the output signal from this logic circuit to provide a first correlation signal S1,
also in performing these operations on the said analogue signals after shifting one of them by a quarter period at the centre frequency of the abovementioned frequency band to provide a second correlation signal S2,
and in summing the absolute values of first and second correlation signals to provide a third correlation signal S that is virtually independent of any time shift between the above-mentioned analogue signals.
Transforming analogue signals into binary logic signals (for which only two distinct values are possible) makes it possible to work on a single bit, and to subsequently employ a logic operator to perform the correlation between the signals. Compared to traditional numerical computation methods, this greatly simplifies the correlation method. In addition, the third correlation signal obtained is virtually independent of the time shift between the signals, and does not require the time shift to be measured.
Through another characteristic of the invention, this method can also be used to transform each analogue signal into a binary logic signal by detecting zero passings of the analogue signal, and in assigning a first logic value to the signal when it is positive, and a second when it is negative.
Detecting zero passings of the analogue signals provides a simple means of obtaining an excellent dynamic range (approximately 60 to 80 dB), which would correspond to at least a resolution of 12 bits in known numerical computation methods.
Through another characteristic of the invention, the method consists also in connecting the output of the logic circuit to a low-pass filter to perform the above-mentioned summing functio

REFERENCES:
patent: 3961172 (1976-06-01), Hutcheon
patent: 4025775 (1977-05-01), Beauvais et al.
patent: 4224679 (1980-09-01), Nossen et al.
IBM Technical Disclosure Bulletin, vol. 23, No. 9, Feb. 1981, pp. 4115-4116.
Wescon Technical Papers, Oct. 30-Nov. 2, 1984, pp. 52-56.
Onde Electrique, vol. 63, No. 6/7. Jun.-Jul. 1983, pp. 52-56.

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