EP0473731B1 - Method and device for comparing two variable analog signals - Google Patents

Description

The invention relates to a method and a device. comparison of two variable analog signals, for example over time, such as audio signals or video, which are either different from each other, or identical but shifted in time.

It is known to compare two signals with each other variable analog, determine a function of correlation between these signals and check from values of this function if there is identity or not between signals.

We use for this calculation methods correlation function, which lead to use steep slope band filters, analog-to-digital converters, a system of information processing allowing calculation in time correlation function, and an algorithm for complex treatment capable of taking into account and compensate for any offset between the signals. The cost systems allowing this calculation is generally quite Student.

We also know various measuring devices phase shift between two analog signals sine waves of the same frequency. However, these devices are not applicable to signals which are not purely sinusoidal, such as audio or video signals received or produced by radio receivers or television.

The document Electronic Design, vol. 37, no. 10, 11 May 1989, p.115, discloses a phase comparator which includes two channels analog signal processing, these two channels each comprising in series transformation circuits from analog signals to binary logic signals, a logic circuit of the exclusive OR type and an establishment circuit of a signal by summation.

We also know, see the document Wescon Technical Papers (1984), Oct. 30 - Nov. 2., pages 1-7, a phase comparator which uses an integrated correlation circuit. This comparator comprises two parallel signal processing channels, one of which includes means for shifting one of the signals over time with respect to the other, the offset being equal to π 2 . Furthermore, said comparator uses a circuit for adding the absolute values of the two correlation signals.

The object of the invention is in particular to simplify the aforementioned methods and systems of numerical computation and therefore greatly lower their cost while retaining the desired speed and accuracy of establishing the correlation.

It also aims to measure correlation between two analog signals of the aforementioned type,   which does not use a time or phase measurement.

• à transformer lesdits signaux analogiques en signaux logiques binaires, à appliquer ces derniers aux entrées d'un circuit logique 32 du type OU exclusif ou multiplieur, puis à appliquer une fonction somme au signal de sortie de ce circuit logique pour obtenir un premier signal de corrélation S1,
• à effectuer également ces opérations sur lesdits signaux analogiques après avoir décalé l'un d'eux d'un intervalle égal à 1/4 de période à la fréquence centrale de la bande de fréquences précitée, pour obtenir un deuxième signal de corrélation S2,
• et à faire la somme des valeurs absolues des premier et deuxième signaux de corrélation pour obtenir un troisième signal de corrélation S sensiblement indépendant d'un décalage dans le temps entre les signaux analogiques précités.

The invention proposes, for this purpose, a method of comparing two variable analog signals consisting in establishing a correlation signal between the analog signals and in verifying from the values of this signal whether there is identity or not between the signals. analog, characterized in that, the signals to be compared being either identical but offset in time, or different, and covering a predetermined frequency band, it consists:

• transforming said analog signals into binary logic signals, applying the latter to the inputs of a logic circuit 32 of the exclusive OR type or multiplier, then applying a sum function to the output signal of this logic circuit to obtain a first correlation signal S1,
• also to carry out these operations on said analog signals after having shifted one of them by an interval equal to 1/4 of period at the center frequency of the aforementioned frequency band, in order to obtain a second correlation signal S2,
• and summing the absolute values of the first and second correlation signals to obtain a third correlation signal S substantially independent of a time shift between the aforementioned analog signals.

Transformation of analog signals into binary logic signals (which can only have two distinct values) allows working on a single bit and then use a logical operator to perform the correlation between the signals. This results in a simplification important of the correlation process compared to classical numerical calculation methods. By elsewhere, the third correlation signal obtained is substantially independent of the time lag between signals to compare, without the need to measure   this shift.

In one embodiment of the invention, this process also consists in transforming each analog signal into binary logic signal by detection of zero crossings of this analog signal, and assigning a first logical value to the signal when positive, and a second logical value when it is negative.

Detection of zero crossing signals analog provides simple excellent dynamic (of the order of 60 to 80dB) which would correspond at least 12 bit resolution within known methods of numerical calculation.

In one embodiment of the invention, the method also consists in connecting the logic circuit output to a low pass filter to achieve the aforementioned sum function.

The invention also provides a device for comparison of two variable analog signals, including means for establishing a correlation signal between these two analog signals and means of comparison of this signal with a predetermined value to check whether there is identity or not between the signals analog, characterized in that, these analog signals being either identical and time-shifted, either different, and covering a predetermined frequency band, this device includes two parallel tracks analog signal processing, one of which includes means for shifting one of the signals over time relative to each other, the offset being equal to 1/4 of period at the center frequency of the frequency band above, these two channels each comprising in series of circuits for transforming analog signals into binary logic signals, a logic circuit of the type multiplier or exclusive OR, an establishment circuit by summing a correlation signal S1, S2, and a   circuit for adding the absolute values of the two signals correlation S1, S2, producing an output signal correlation S substantially independent of an offset in the time between the above analog signals.

A low-pass filter at the output of each circuit logic provides the value of the correlation signal S1, S2 corresponding to a given offset between analog signals.

The absolute enhancement of these correlation S1, S2 and the addition of their absolute values allow this shift between the signals to compare.

Advantageously, the output of the addition circuit is connected to the input of a low-pass filter, realizing smoothing the correlation signal.

This avoids the disadvantages associated with the comparison of these signals at times when they have very low values.

Preferably, the device according to the invention also includes leveling circuits as input analog signals, such as for example automatic gain control circuits, and filters band pass.

The circuits for transforming analog signals into binary logic signals are advantageously circuits for comparing analog signals to a determined value, in particular the value zero, allowing the detection of passages of analog signals by zero and the attribution to these signals of two binary values depending on whether they are positive or negative .

In general, the cost of a device according to the invention is far inferior to that of the devices classics of numerical computation of a function of correlation, and its performance is excellent.

• la figure 1 représente schématiquement un exemple d'application du dispositif de corrélation selon l'invention;
• la figure 2 représente schématiquement les circuits essentiels du dispositif selon l'invention;
• les figures 3, 4 et 5 sont des graphes représentant des variations de signaux de corrélation en fonction du déphasage entre deux signaux analogiques comparés;
• la figure 6 représente schématiquement une variante de réalisation du dispositif selon l'invention.

The invention will be better understood and other characteristics, details and advantages thereof will appear more clearly on reading the description which follows, given by way of example with reference to the appended drawings in which:

• FIG. 1 schematically represents an example of application of the correlation device according to the invention;
• FIG. 2 schematically represents the essential circuits of the device according to the invention;
• Figures 3, 4 and 5 are graphs showing variations in correlation signals as a function of the phase shift between two compared analog signals;
• FIG. 6 schematically represents an alternative embodiment of the device according to the invention.

To better understand the interest of the invention, we first refer to Figure 1 which represents an example of application of the method and the device according to the invention.

Reference 10 designates a radio receiver or television, connected to an antenna 12 and associated with a apparatus 14 for detecting the frequency on which is tuned the receiver 10.

This device 14 includes a reference receiver 16, also connected to the antenna 12, a device correlation 18 according to the invention, a microprocessor 20 information processing, memory 22 data logging, an interface circuit 24 electronics to control receiver 16 under microprocessor control 20, and a dating clock 25.

The outputs of receivers 10 and 16 are connected at the inputs of the correlation device 18, the output is connected to an input of the microprocessor 20. This, by means of the interface 24, performs a scanning systematic of the frequencies received by the receiver 16 of   reference, whose output signals are compared to those of the receiver 10 by the device 18. The correlation between these signals establishes that receivers 10 and 16 are set to the same frequency. Correlation dates and the corresponding frequencies are saved in memory 22 from which they can then be extracted and used.

Figure 2 shows schematically the constitution of a correlation device 18 according to the invention.

In this device, audio or video signals produced by receptors 10 and 16 are applied to input circuits including circuits 26 of upgrade, such as automatic control circuits gain, generating analog signals with determined maximum voltage levels, and filters bandpass 28, reducing the frequency range signals at a predetermined band.

The bandwidth of the filters 28 is by example of an octave or more (e.g. 500-1000 Hz) for audio signals. For video signals, it is for example from 500 kHz to 1 MHz.

The output of each filter 28 is applied to the input of an analog signal transformation circuit 30 in binary logic signal compared to a predetermined value, which is preferably the value zero. The circuits 30 can therefore be simple comparators, whose positive inputs receive signals filters 28 and whose negative inputs are connected to ground.

The outputs of the two comparators 30 are connected to the two inputs of a logic circuit 32 of the OR type exclusive, whose output signal is a logic signal binary, high level (e.g. 1) when both input signals are identical, and low level (0 or -1), when the two input signals are different. The   function of circuit 32 is therefore equivalent to a multiplication logic.

The output of circuit 32 is connected to a filter low pass 34 which performs a summation of the output of logic circuit 32, and which produces a signal correlation between the signals to be compared.

We know that a correlation function is of the type given by the following relation:

where: x (i) and y (i) are the signals to compare,
τ is the offset between the signals.

Circuit 34 provides this function of creation for a zero value of the offset between the signals. One thus obtains at the output of circuit 34 a signal S1 which is equal to the correlation signal S0 between the signals to compare when their offset is zero and which is less than this signal when there is an offset between the signals to be compared.

The variation of the S1 / S0 ratio has been represented in Figure 3 as a function of a phase shift between the signals to be compared.

We see that this ratio is equal to 1 when the phase shift is zero or multiple of 2 π, that it is equal to 0 for phase shifts of 90 degrees, 270 degrees etc ... and that it is equal to -1 for phase shifts of π, 3 π, etc. (the variation of this ratio between the values 1 and -1 assumes that the binary values of the output signal from the logic circuit 32 are 1 and -1).

The graph in Figure 3 shows that we have makes a total loss of correlation at the output of the circuit 34 when the phase difference between the signals to be compared is close to π / 2, 3π / 2, etc. We can eliminate this drawback, by comparing the analog signals a second time   initials, after having shifted one of them from 90 degrees. The invention provides (Figure 2) that the outputs circuits 28 are connected to the inputs of a circuit 36 adding a quarter shift T / 4 to the frequency central filter bandwidth 28 to one of the analog signals, relative to the other signal analog. The outputs of circuit 36 are connected to the positive inputs of comparators 30 whose outputs are connected to the inputs of a logic circuit 32 identical to circuit 32 previously described. The exit of this logic circuit is connected to the input of a filter low pass 34 with comparable S2 output signal to the aforementioned output signal S1, but is offset by compared to this one. The graph in Figure 4 represents the variation of the S2 / S0 ratio as a function of a phase shift between the signals to be compared.

We see that it is enough to add one to the other the absolute values of the S1 / S0 and S2 / S0 ratios to obtain a ratio which is constant and equal to 1, whatever or the phase shift between the signals.

According to the invention, the outputs of the filters 34 are therefore connected to the inputs of circuits 38 absolute value (e.g. rectification circuits double alternation) whose outputs are connected to the inputs of an adder circuit 40. The output signal S of circuit 40 is a correlation signal which is substantially independent of the offset between the signals to be compared, and whose variation in the ratio to the correlation signal S0 is shown in Figure 5.

This signal S can be applied to the input of a smoothing circuit 42 such as a low-pass filter, the output is connected to the positive input of a comparator 44. The negative input of this comparator receives a voltage of predetermined value to which the output signal from circuit 42. The output signal from comparator 44 is applicable to an input of the microprocessor   20 of the apparatus 14 of FIG. 1.

The operation of this device follows from the above:
the audio or video signals produced by the receivers 10 and 16 are applied to the leveling circuits 26, then processed by the bandpass filters 28 and transformed into binary logic signals by the comparators 30. They are then compared with each other by the logic circuit 32, a first time directly, a second time after one of these signals has undergone a shift of a quarter of a period at the center frequency of the pass band of the filters 28, correlation signals are established by the low-pass filters 34, and the absolute values of these signals are added to obtain a correlation signal little dependent on the offset between the initial analog signals. This correlation signal is smoothed and compared to a predetermined value. If it is greater than this value, the analog signals will be considered to be identical, while they will be considered to be different from each other if the correlation signal is less than the predetermined value.

The correlation device, whose components essentials have been represented in figure 2, is therefore relatively simple and has the important advantage of work on a single bit, unlike systems comparable numerical computations used in the art anterior, which generally work on 8 or 16 bits of digital resolution.

An alternative embodiment of the device is shown schematically in Figure 6. In this variant, the output of each exclusive 32 OR driver circuit an up-down circuit 46, which counts by increase when the output signal of circuit 32 is level +1, and by decrease when this output signal is at level -1. A timer circuit 48 associated with   a clock 50 periodically resets the circuits 46. After a time T, the sum of the absolute values contents of the two circuits 46 is calculated by a adder circuit 52 and compared by a circuit 54 to a double threshold (symmetrical thresholds with respect to zero). The output of comparator 54 provides a decision signal of correlation or non-correlation between the signals initial analogs.

The adder circuit 52 performs either the sum of signals S1 and S2 of circuits 46 when they are of the same sign, that is to say their subtraction when they are of opposite sign. It is controlled for this by bits of sign s1 and s2 of signals S1 and S2.

The invention is of course applicable to other analog signals than audio and video signals, and it also applies to analog signals which vary according to another parameter than the weather.

Claims (14)

1. Method for comparing two variable analogue signals, consisting in establishing a correlation signal between analogue signals and verifying from the values of this signal whether or not the analogue signals are identical, characterized in that the signals to be compared being either identical but exhibiting a time shift, or different, and covering a preset frequency band, it consists in:

   transforming the said analogue signals into binary logic signals, in order to apply the latter to the inputs of a logic circuit (32) of the exclusive-OR or multiplier type, then applying a summing function to the output signal of this logic circuit so as to obtain a first correlation signal S1,

   also performing these operations on the said analogue signals after shifting one of them by a 1/4 period at the centre frequency of the above-mentioned frequency band so as to obtain a second correlation signal S2.

   and in summing the absolute values of the first and second correlation signals so as to obtain a third correlation signal S that is virtually independent of any time shift between the above-mentioned analogue signals.
2. Method according to claim 1, characterized in that it consists in smoothing the third correlation signal S before comparing it to a preset value to verify identity or non-identity between the above-mentioned analogue signals.
3. Method according to claim 1 or 2, characterized in that it consists in selecting the above-mentioned frequency band within a frequency range covered by the analogue signals, and to consider only variations of these signals within the said frequency band.
4. Method according to any preceding claim, characterized in that it consists in transforming each analogue signal into a binary logic signal by detecting zero passings of this analogue signal, and by assigning a first logical value to the signal when it is positive and a second logical value when it is negative.
5. Method according to any preceding claim, characterized in that it consists in connecting the output of the logic circuit (32) to a low-pass filter (34) to achieve the above-mentioned summing function.
6. Method according to any one of claims 1 to 4, characterized in that it consists in connecting the output of the logic circuit (32) to an up-down counter (46) to achieve the above-mentioned summing function.
7. Method according to any preceding claims, characterized in that the analogue signals to be compared are audio signals produced for example by radio receivers, or video signals produced for example by television receivers.
8. Device for comparing two variable analogue signals, comprising means for establishing a correlation signal between these two analogue signals and means (44) for comparing this signal with a preset value in order to verify whether or not identity exists between the analogue signals, characterized in that these analogue signals are either identical and shifted in time, or different, and covering a preset frequency band, the device comprising two parallel channels for processing analogue signals of which one comprises means (36) for introducing a time shift of one signal relative to the other, this shift being equal to a 1/4 period at the centre frequency of the above-mentioned frequency band, each of these two channels including a series of circuits for transforming analogue signals into binary logic signals, a logic circuit (32) of the multiplier or exclusive-OR type, a circuit (34) for establishing a correlation signal S1, S2 by summing, and a circuit (38, 40, 52) for adding the absolute values of the two correlation signals S1, S2, producing at the output a correlation signal S that is virtually independent of any time shift between the above-mentioned analogue signals.
9. Device according to claim 8, characterized in that the output of adder circuit (40) is connected to the input of a low-pass filter (42) that smooths correlation signal S.
10. Device according to claim 9, characterized in that it comprises at the output a circuit for comparing correlation signal S with a preset threshold.
11. Device according to claims 8 to 10, characterized in that the circuit for establishing each correlation signal S1, S2 by summing is a low-pass filter (34) whose output is connected to a circuit that provides absolute values (34) such as a full-wave rectifier.
12. Device according to claim 8, characterized in that the circuit for establishing each correlation signal S1, S2 is an up-down counter (46) associated with a periodic reset circuit (48).
13. Device according to one of the claims 8 to 12, characterized in that it comprises input circuits each of which is made up of a level-matching circuit (26) such as an automatic gain control circuit, and a bandpass filter (28) whose passband corresponds to the above-mentioned preset frequency band.
14. Device according to one of the claims 8 to 13, characterized in that the binary logic signal transforming circuits comprise circuits (30) for comparing analogue signals with a given value, particularly zero.