DETECTION ARRANGEMENT FOR DETECTION OF SIGNAL VARIATIONS IN A SIGNAL

Abstract: In the detection arrangement (1), to an input (5) of which is supplied a signal, the signal is processed by a signal processing device (2) comprising a threshold circuit (3) followed by a signal hold circuit (6) to a reference signal formed at an output (12) of the signal hold circuit (6). The signal supplied to the input (5) of the detection arrangement (1) and the reference signal formed at the output (12) of the signal hold circuit (6) are supplied to a comparison circuit (9). The signal processing device (2) ensures that the reference signal formed at the output (12) of the signal hold circuit (6) follows peaks and valleys of the signal except for a difference value, the reference signal assuming a threshold value when a peak or a valley is reached. If the signal varies within a range determined by the difference value around the threshold value, the signal hold circuit (6) holds the threshold value, as a result of which noise influences are eliminated upon detection of peaks and valleys in signals. According to the invention, the signal processing device (2) comprises adjusting means for adjusting the difference value, as a result of which adaption to various signal-to-noise conditions is possible.

Description: The invention relates to a detection arrangement for detection of signal variations in a signal comprising a signal processing device for processing the signal to a reference signal and further a comparison circuit having a first input for the supply of the signal and a second input for the supply of the reference signal, an output of the comparison circuit having a first state if the signal has a smaller signal value than the reference signal and a second state if the signal has a larger signal value than the reference signal, while the signal processing device comprises a threshold circuit providing a variable threshold value and having an input for the supply of the signal, which threshold value depends upon the signal value of the signal, an output of this threshold circuit being coupled to an input of a signal hold circuit for holding the variable threshold value forming the reference signal, while, when the variable threshold value is passed with a difference value by the signal in a first and a second direction, respectively, the variable threshold value follows the signal except for the difference value. Such a detection arrangement can generally be used, for example, to detect signals disturbed by noise, such as, for example, pulsatory signals. Such a detection device is known from US-A-3,708,678, in which Figure 1 shows a comparison circuit (A2), in which a signal is supplied to a first input ( - ) and the signal is supplied to a second input ( + ) via two antiparallel connected diodes and a capacitor. The signal processing circuit is therefore constituted by the diodes and the capacitor. Peaks and valleys of a signal supplied to the detection circuit can be followed, except for a difference value, such as, for example, a diode threshold voltage of a forward biased diode, also if the signal is disturbed by noise. As is described in column 4 on lines 3-10, also larger difference values than one diode threshold voltage may be attained by arranging diodes in series in the antiparallel combination. If a different number of diodes are arranged per branch in the antiparallel combination, it is achieved that for the signal directions unequal difference values are obtained. A disadvantage of the detection device described in the aforementioned US Patent Specification is that the detection device cannot be adapted to different signal-to-noise conditions, as a result of which the device cannot operate satisfactorily in unfavourable signal-to-noise conditions and/or at comparatively small signals. The invention has for its object to provide a detection device, which inter alia is unfavourable signal-to-noise conditions will operate satisfactorily. A detection device of the kind mentioned in the opening paragraph is for this purpose characterized in that the threshold circuit further comprises adjusting means for adjusting the difference value in accordance to the signal-to-noise condition of the signal, the adjusting means being coupled to the input and output of the signal processing device, for receiving said input and said output respectively. An embodiment of a detection device according to the invention is characterized in that the adjusting means comprise a differential amplifier, a first input of which is coupled to the input of the threshold circuit, an output of which is coupled to an antiparallel combination of rectifier elements and a second input of which is coupled to a centre tapping of a variable voltage divider, which is coupled at one side to the output of the differential amplifier and at another side to the output of the signal processing device. As a result, the difference value is adjustable from zero to a (multiple of) (a) threshold value(s) of a forward biased rectifier element. If a different number of rectifier elements are arranged in the branches of the antiparallel combination, for the signal directions an unequal difference value will occur. A further embodiment of a detection device according to the invention, in which the signal hold circuit comprises a hold element for holding the variable threshold value, is characterized in that the signal hold circuit further comprises a buffer amplifier, of which the input is coupled to the hold element, which is coupled to the input of the signal hold circuit, the output of the buffer amplifier being coupled to the output of the signal hold circuit. The hold element, for example a capacitor, can have a comparatively small capacitance value; the buffer amplifier, when constructed, for example, as an operational amplifier, will have a high-ohmic input. In such an embodiment, the detection device will be suitable for comparatively low to comparatively high frequencies. The invention will be described more fully with reference to the accompanying drawing, in which: Figure 1 shows the principle circuit diagram of a detection arrangement, Figure 2 shows for explanation of the operation of the detection arrangement a signal together with the variation of the reference signal and a threshold value therein and further an output signal of the comparison circuit, Figure 3 shows an embodiment of a threshold circuit in a detection arrangement, Figure 4 shows a first embodiment of adjusting means for adjusting the difference value in a detection arrangement according to the invention, Figure 5 shows a second embodiment of adjusting means for adjusting the difference value in a detection arrangement according to the invention, and Figure 6 shows an embodiment of a signal hold circuit in a detection arrangement according to the invention. Figure 1 shows the principle circuit diagram of a detection arrangement 1. The arrangement 1 comprises a signal processing device 2. The signal processing device 2 comprises a threshold circuit 3, of which an input 4 is coupled to an input 5 of the detection arrangement 1. Further, the signal processing device 2 comprises a signal hold circuit 6, of which an input 7 is coupled to an output 8 of the threshold circuit 3. The detection arrangement 1 further comprises a comparison circuit 9, of which a first input 10 is coupled to the input 5 of the detection arrangement 1 and of which a second input 11 is coupled to an output 12 of the signal hold circuit 6. The detection arrangement 1 is provided with an output 13, which is coupled to an output 14 of the comparison circuit 9. The operation of the arrangement will be explained more fully with reference to Figure 2, in which a signal i for supply to the input 5 of the detection arrangement 1 together with the variation of a reference signal r appearing at the output 12 of the signal hold circuit 6 and further an output signal c at the output 14 of the comparison circuit 9 as a function of the time t . t1 to t6 indicate a few time instants. Δ designates a difference value and vt1, vt2 and vt3 designate variable threshold values. For the further description it is assumed that the signal i is a signal of which a direct current component is restored, while in Figure 2 the signal i is indicated with respect to a zero level p . It is assumed that the detection arrangement 1 is provided with supply terminals (not shown) for connecting a supply voltage including mass potential. For the description of the operation of the detection arrangement 1, it is assumed that the signal i is applied to the input 5 of the detection arrangement 1 and that the supply voltage is connected. Further, in an initial condition it is assumed that the signal i has the zero level p , that the output 12 of the signal hold circuit 6 has the difference value Δ and that the output 14 of the comparison circuit 9 has a state s1. As long as the signal i lies below the variable threshold value vt1, the threshold value vt1 will be held by the signal hold circuit 6. When the signal i passes the reference signal r having the threshold value vt1 at the instant t1, the output 14 of the comparison circuit 9 passes from the state s1 to a state s2. The reference signal r and hence the threshold value vt1 do not vary. The reference signal r will not vary upon increase of the signal i until the signal between the signal i and the threshold value vt1 amounts to the difference value Δ. This occurs at the instant t2. With a further increase of the signal i , from the instant t2 the reference signal r will follow the signal i except for the difference value Δ. When the signal i reaches a pulse peak M at the instant t3, the reference signal r does not increase further and a new variable threshold value vt2 has been adjusted. If the pulsatory signal i decreases from the instant t3 and passes the reference signal r at the instant t4, the output 14 of the comparison circuit 9 passes from the state s2 to the state s1, but the reference signal r then retains the threshold value vt2 until the signal i falls below the threshold value vt2 at the different value Δ. The reference signal r will follow the signal i from the instant t5. With a further increase of the signal i , the reference signal r follows the signal i except for the difference value Δ. At the instant t6, at which the signal i reaches a pulse valley m , a new state of equilibrium is adjusted, the reference signal r remains constant and a new threshold value vt3 has been adjusted. With a following increase or decrease of the signal i , the process described is repeated and the threshold value is adapted dynamically to the signal i . The difference value Δ around the threshold value, which produced by the threshold circuit 3, renders the detection arrangement 1 to a certain extent insensitive to noise superimposed on the signal i , as far as the latter lies in a range determined by the difference value Δ. Figure 3 shows an embodiment of a threshold circuit 3. The threshold circuit 3 comprises a first (15) and a second (16) rectifier element connected in parallel opposition and coupled to the input 4 and the output 8, respectively, of the threshold circuit 3. In the embodiment, diodes are shown as rectifier elements. A forward voltage drop th of the diodes forms the difference value Δ. Several diodes can be arranged in series in each branch. Figure 4 shows a first embodiment of adjusting means for adjusting the difference value Δ, in which the threshold circuit 3 is coupled in the manner described to the signal hold circuit 6. The adjusting means forming part of the threshold circuit 3 comprise a differential amplifier 22, of which a first input 23 is coupled to the input 4 of the threshold circuit 3. An output 24 of the differential amplifier 22 is coupled to the rectifier elements 15 and 16. A voltage divider comprising a series-combination of resistors R1 and R2 is coupled through a junction point of the resistors R1 and R2, a centre tapping 25, to a second input 26 of the differential amplifier 22. Further, R1 is coupled by its other side to the output 24 of the differential amplifier 22 and R2 is coupled by its other side through a connection terminal 27 to the output 12 of the signal hold circuit 6. In a practical situation, the voltage divider is chosen to be variable and is, for example, a potentiometer. By the adjusting means shown, a difference value Δ can be adjusted so that adaptation to the signal-to-noise ratio of the signal i is possible. With the use of, for example, a diode as rectifier element with the forward voltage drop th, the difference value is: Δ = {R2/(R1 + R2)} · th, which can simply be varified with reference to the circuit shown. The difference value Δ is therefore adjustable between Δ = 0 and Δ = th. Figure 5 shows a second embodiment of the adjusting means for adjusting the difference value Δ, which adjusting means are included in the threshold circuit 3. The differential amplifier 22 and the resistors R1 and R2 are arranged in the same manner as in Figure 5. The adjustment of the difference value Δ is obtained in the embodiment shown by arranging parallel to R2 a field effect transistor FET connected as a variable resistor, a terminal 28 of the resistor R2 being connected to a resistor Rd, which resistor Rd is further connected to the drain electrode of the field effect transistor FET, while another terminal 29 of the resistor R2 is connected to the source electrode of the field effect transistor FET. When the field effect transistor FET is driven at its gate electrode at a control input 30, the equivalent resistor R2′ of the parallel-combination of the resistor R2 and the field effect transistor FET is varied. In the said formula of the difference value Δ, R2 should then be replaced by R2′. The gate electrode of the field effect transistor FET may be driven, for example, from a digital-to-analog converter with a current output (not shown), as a result of which the difference value Δ of the detection arrangement 1 can be driven from a computer (not shown). Figure 6 shows an embodiment of a signal hold circuit 6, according to the invention, which comprises a hold element 17, which is coupled to the input 7 of the signal hold circuit 6 and further to a connection terminal 18 for the mass potential. The signal hold circuit 6 further comprises a buffer amplifier 19, of which an input 20 is coupled to the hold element 17 and of which an output 21 is coupled to the output 12 of the signal hold circuit 6. In the embodiment shown, a capacitor is chosen as hold element and the buffer amplifier 19 ensures that the hold element 17 is not leaded by further circuits coupled thereto. The invention is not limited to the embodiments shown, but many variations are possible for those skilled in the art within the scope of the invention. For example, the field effect transistor FET in the threshold circuit 3 may be connected parallel to R1 instead of parallel to R2. Further, the parallel-combination of the field effect transistor FET and R1 and R2 may be replaced by an element, whose resistance value can vary under influence of light, such as light-dependent resistor in one housing with light source.

Claims: 1. A detection arrangement (1) for detection of signal variations in a signal (i) comprising a signal processing device (2) for processing the signal (i) to a reference signal (r) and further a comparison circuit (9) having a first input (10) for the supply of the signal (i) and a second input (11) for the supply of the reference signal (r), an output (14) of the comparison circuit (9) having a first state if the signal (i) has a smaller signal value than the reference signal (r) and a second state if the signal has a larger signal value than the reference signal (r), while the signal processing device (2) comprises a threshold circuit (3) providing a variable threshold value (vt1, vt2, vt3) and having an input (4) for the supply of the signal (i), which threshold value (vt1, vt2, vt3) depends upon the signal value of the signal (i), an output of this threshold circuit (3) being coupled to an input (7) of a signal hold circuit (6) for holding the variable threshold value (vt1, vt2, vt3) forming the reference signal (r), while, when the variable threshold value (vt1, vt2, vt3) is passed with a difference value (Δ) by the signal (i) in a first and a second direction, respectively, the variable threshold value (vt1, vt2, vt3) follows the signal (i) except for the difference value (Δ), characterized in that the threshold circuit (3) further comprises adjusting means (22, R1, R2, FET) for adjusting the difference value (Δ) in order to adapt the detection arrangement to various signal-to-noise conditions, the adjusting means being coupled to the input (4) and to the output (12) of the signal processing device (2), for receiving said input (4) and said output (12) respectively. 2. A detection arrangement as claimed in Claim 1, characterized in that the adjusting means comprise a differential amplifier, a first input of which is coupled to the input of the threshold circuit, an output of which is coupled to an antiparallel combination of rectifier elements and a second input of which is coupled to a centre tapping of a variable voltage divider, which is coupled at one side to the output of the differential amplifier and at another side to the output of the signal processing device. 3. A detection arrangement as claimed in Claim 1 or 2, in which the signal hold circuit comprises a hold element for holding the variable threshold value, characterized in that the signal hold circuit further comprises a buffer amplifier, of which the input is coupled to the hold element, which is coupled to the input of the signal hold circuit, the output of the buffer amplifier being coupled to the output of the signal hold circuit.

Inventors: BOLK, HENDRIK JOHANNES JAN, ZIELTJENS, GWORGES CHARLES PETRONELLA
Applicants: N.V. PHILIPS' GLOEILAMPENFABRIEKEN
Application year: 1988
Main classification: H03K5
IPC codes: H03K5, G06G7