JP4370577B2 - Signal extraction method and signal extraction circuit - Google Patents

Description

  The present invention relates to a signal extraction method and a signal extraction circuit suitable for extracting a component of the signal from a modulated wave in which a minute signal is superimposed on a carrier wave.

  A modulated wave in which a minute signal having a relatively high frequency is superimposed on a carrier wave having a relatively low frequency is used in various fields. In order to distinguish from a “signal” in a general sense, a signal superimposed on a carrier wave as described above is specifically referred to as a “target signal” herein. When extracting a target signal from the above-described modulated wave, it is considered to use a differentiation circuit using an operational amplifier (so-called operational amplifier).

Incidentally, a general differentiating circuit includes, for example, an inverting input terminal IN ⁻ to which a signal is input, a non-inverting input terminal IN ⁺ to which a reference voltage Vref is input, and a positive / negative DC power supply as shown in a broken line frame in FIG. An operational amplifier (opamp) OP having an input terminal, a differentiation capacitor C1 and an input resistor R1 connected in series to the inverting input terminal of the operational amplifier circuit OP, and an output terminal and an inverting input terminal of the operational amplifier OP iN ^- configured with connected and a feedback resistor R2 and the high frequency eliminating capacitor Cnc between. The modulated wave to be processed is input from the input resistor R1 through the capacitor C1 to the inverting input terminal IN ⁻ of the operational amplifier OP, and used as an output of the operational amplifier OP.

Here, when the capacitance of the differentiation capacitor C1 is c1, the resistance value of the input resistor R1 is r1, the resistance value of the feedback resistor R2 is r2, and the capacitance of the high frequency removing capacitor Cnc is cnc, the differentiation in the differentiation circuit is performed. Cut-off frequency fi of operation (proportional relationship between input signal frequency and gain) is fi = 1 / (2π · r1 · c1).
The cutoff frequency fo for high frequency rejection is fo = 1 / (2π · r 2 · cnc)
It becomes. When such a differentiation circuit is used for the extraction of the target signal described above, the differentiation upper limit frequency fi is set to be higher than the frequency of the carrier wave and lower than the frequency of the target signal. Further, the cutoff frequency fo for high frequency removal is set to be higher than the frequency of the target signal.

  By the way, when a modulated wave obtained by modulating a carrier wave composed of a rectangular wave as shown in FIG. 9A, for example, with a minute target signal is input to the differentiating circuit configured as described above, the output signal is shown in FIG. 9B. This is shown as a signal waveform a. That is, when the modulation wave changes greatly at time A, the output signal of the operational amplifier OP increases instantaneously. Accordingly, charges are accumulated in the capacitors C1 and Cnc, respectively, and the charges accumulated in these capacitors C1 and Cnc are gradually discharged through the input resistor R1 and the feedback resistor R2, respectively. Therefore, it cannot be denied that it takes a long time for the output signal to return to the vicinity of the base line (0 V) as shown in the signal waveform a. That is, since the return time of the output signal is long, it takes a long time before the target signal can be determined with reference to the baseline.

  Incidentally, when the value of the feedback resistor R2 is reduced, the output signal is shown as a signal waveform b in FIG. 9B, and the return time to the baseline can be shortened. However, on the other hand, since the signal amplitude becomes small, it becomes difficult to detect the target signal. That is, in a general differentiation circuit, there is a problem that a request for shortening the recovery time and a request for increasing the amplification factor conflict. Such a problem is not limited to the rectangular wave described above, but a carrier wave having a large change at the discontinuity point, such as a triangular wave or a sawtooth wave, in other words, a carrier wave having a large differential value at the discontinuity point is used. It happens in the same way.

  In particular, as shown in FIGS. 10A, 10B, and 10C, output signal waveforms obtained when first-order differentiation and second-order differentiation are performed on a modulated wave having a rectangular wave, a triangular wave, and a sine wave as carrier waves, respectively. In a differentiating circuit using a general amplifier, there is a problem that not only the carrier component cannot be sufficiently removed but also a minute signal component cannot be sufficiently amplified and extracted. Moreover, there is a problem that the level of the differential waveform changes greatly at the discontinuous points of the carrier wave.

  Also, if there is a large difference between the amplitude of the carrier wave and the amplitude of the target signal superimposed on this carrier wave, the carrier component cannot be sufficiently attenuated using a general differentiating circuit. There is a problem that the carrier component remains as noise in the signal. Specifically, even if the frequency ratio between the carrier wave and the target signal is x [dB] in the most general differentiating circuit, if the amplitude ratio is 1 / x [dB], the SN ratio is [1]. ]. Although there are filter circuits having a greater attenuation slope than the differentiation circuit, the above-mentioned problem cannot be solved because of poor response performance. Moreover, the same problem occurs not only in the case of a carrier wave having a large change at a discontinuous point such as the above-described square wave, triangular wave, and sawtooth wave, but also in the case of a carrier wave having a smooth waveform such as a sine wave.

On the other hand, in order to solve the problem of a long recovery time when a signal including an excessive differential component is input in a general differential circuit, for example, as shown in FIG. 11, in parallel with the feedback resistor R2 described above, It has been proposed to provide two diodes (feedback voltage limiting means) D1 and D2 connected in antiparallel with each other (see, for example, Patent Document 1). The diodes D1 and D2 limit the output when the amplitude (voltage) of the output signal exceeds the forward bias voltage VL of the diodes D1 and D2, and only when the output signal does not exceed the forward bias voltage VL. It functions so as to perform almost the same operation as in the prior art.
JP-A 64-43765

  However, the differentiating circuit described in Patent Document 1 is not intended for application to extract a minute target signal from a modulated wave. However, assuming that the differentiating circuit shown in Patent Document 1 is applied to this type of application, the following problems arise. In other words, in the conventional general differentiation circuit shown in FIG. 8 described above, when a signal including an excessive differential component that reaches the limit of the power supply capacity and saturates the output of the operational amplifier OP is input, Is, for example, shown as a signal waveform c in FIG. 12, and its recovery time becomes longer. In this regard, according to the differentiation circuit disclosed in Patent Document 1, when an excessive differential component is included in the input signal, the output signal is suppressed by the feedback voltage limiting means (diodes D1, D2) described above. The signal is shown as a signal waveform d in FIG. Therefore, the recovery time does not increase much compared to when the input signal does not contain an excessive differential component.

  In other words, when the input signal includes an excessive differential component by providing the feedback voltage limiting means (diodes D1, D2), the recovery time is shorter than that of the conventional general differential circuit shown in FIG. It can be shortened. However, in other cases, since the signal waveform d shown in FIG. 12 corresponds to the signal waveform a shown in FIG. 9B, the operation is almost the same as that of the conventional circuit. The trade-off relationship between the demand and the demand for increasing the amplification factor still remains. Therefore, the problem that a minute target signal cannot be accurately extracted due to the influence of the carrier component cannot be solved.

  The present invention has been made in consideration of such circumstances, and its object is to provide a signal extraction method and a signal extraction circuit with a simple configuration capable of amplifying and reliably extracting a minute target signal superimposed on a carrier wave. Is to provide.

  The basic technical idea of the present invention is that, when a minute target signal is extracted from a modulated wave, the request for shortening the recovery time described above is discarded, the recovery time is lengthened, and the absolute value of the output signal is decreased. Sensitive to the change to, and conversely insensitive to the change to the direction in which the absolute value of the output signal increases, among the target signal components included in the modulated wave, It tries to emphasize the side closer to the baseline.

  That is, the request for a general differentiation circuit is to increase the amplification factor and shorten the discharge time constant, but in the present invention, the amplification factor of the differentiation circuit is maximized and the discharge time constant is also increased. I try to maximize it. When removing a carrier wave in a general differentiating circuit, exclusively, “when the change in the carrier wave is small, the output is made zero as soon as possible”, but in the present invention, “when the carrier wave change is small , Make changes in output as small as possible. The difference between these technical ideas is whether to focus on the “value” of the output or on the “change”.

  By the way, at the discontinuity point of the carrier wave, the SN ratio of the carrier wave and the signal component is approximately [1], and it is difficult to distinguish them. However, when there is no change in the carrier wave, if the amplification factor for the signal component is sufficiently large, the influence of the carrier wave is simply to say where the output vector immediately after the discontinuity starts, and its initial value deviates somewhat. Only. Therefore, when the change in the carrier wave is small, the signal component can be reliably extracted by making the change in the output as small as possible.

Therefore, the signal extraction method according to the present invention includes a fundamental frequency component lower than that of the target signal and includes a differential value larger than the target signal or an amplitude larger than the target signal. When extracting a signal component of the target signal (micro signal) from a modulated wave in which the target signal is superimposed on a carrier wave, for example, a modulated wave in which a micro signal is superimposed on a rectangular wave or a triangular wave, the modulation signal is obtained after differential processing. The logarithmic conversion function is dominant when the differential value is large, and the integral function is dominant when the differential value is small , and logarithmic conversion processing and integration processing are simultaneously performed on the differential value . Yes.

By the way, in the logarithmic transformation process and the integration process, when the self-impedance is high (high resistance region), the integration function is dominant, and when the self-impedance is low (low resistance region), the logarithmic transformation function is dominant. Simultaneously using an amplifier having conversion characteristics . The term “dominant” refers to which of the integration function and the logarithmic conversion function strongly acts on the differential value. The signal component of the target signal not only extracts the target signal itself, but also a part of the information held by the target signal, specifically, the timing at which the target signal crosses a threshold (for example, the baseline) and the change in the information. This shows a case where direction information is extracted.

  In particular, in the signal extraction method according to the present invention, as to the logarithmic transformation process and the integration process, the change over time of the target signal to be extracted is such that the extracted target signal is a mountain to valley, Alternatively, it is desirable to execute so as to pass through a certain threshold value when shifting from a valley to a mountain. Note that the above-described constant threshold is typically a baseline of 0V, but may be an offset from the baseline.

  In addition, the differential processing is performed using a capacitor as described in claim 3, and the logarithmic conversion processing and integration processing are performed using a feedback type in which feedback impedance is determined using at least a pair of semiconductor junctions connected in antiparallel. It is desirable to carry out using an amplifier. Furthermore, it is also useful to repeat the signal extraction method described above a plurality of times by regarding the extracted signal as a modulated wave as described in claim 4.

The signal extraction circuit according to the present invention includes a fundamental frequency component lower than that of the target signal and includes a differential value larger than the target signal or an amplitude larger than the target signal. A signal component of the target signal is extracted from a modulated wave in which the target signal is superimposed on a carrier wave. The signal component includes a signal input terminal and a reference input terminal, and amplifies and outputs the modulated wave input through a capacitor. And an amplifier that feeds back the output of the amplifier to a signal input terminal of the amplifier. The feedback means has an impedance that increases when a voltage between the input and output of the amplifier is small. characterized in that the arrangement as to change the self-impedance exponentially so that the impedance becomes large when the voltage between a large It is.

  Preferably, the feedback means is realized as a pair of semiconductor junctions (diodes) connected in antiparallel. According to a seventh aspect of the present invention, when the voltage between the input and output terminals of the amplifier is smaller than the conduction voltage of the pair of semiconductor junctions connected in reverse parallel as the feedback means, that is, as an operational amplifier, that is, It is desirable to operate as a linear amplifier with a constant gain and to operate substantially as a comparator when the voltage between the input and output terminals is larger than the conduction voltage of the semiconductor junction.

  Further, as described in claim 8, the feedback means in the feedback operational amplifier is constituted by only a pair of semiconductor junctions connected in antiparallel and a high frequency removing capacitor connected in parallel to these semiconductor junctions. May be. However, by configuring the feedback means with a diode, the feedback operational amplifier can have the same function as the bidirectional peak hold circuit. In this case, since the peak hold operation of the feedback operational amplifier can be roughly regarded as an integration operation, the above-described high frequency removing capacitor can be omitted.

  It is also useful to use a signal extraction circuit having the above-described configuration as one structural unit, and connect a plurality of structural units in multiple stages. In this case, in order to remove noise, an amplification limiting resistor may be provided in parallel with the aforementioned diode in the subsequent differentiation circuit. By the way, when there is no resistance, the noise is greatly amplified and cannot be distinguished from the signal. Therefore, it is desirable to facilitate the distinction between noise and signal by limiting the amplification factor by putting a resistor in parallel with the diode.

  According to the signal extraction method of the present invention, after differential processing of the modulated wave, logarithmic conversion processing and integration processing are performed on the obtained differential value, so that a large differential waveform generated at the discontinuity point of the carrier by the differentiation processing It is possible to amplify only a minute signal component superimposed on the carrier wave with a large amplification factor. In particular, since a signal in which a large change at a discontinuous point is suppressed by differentiation is subjected to logarithmic conversion processing and integration processing, the signal can be amplified and extracted with a large amplification factor in accordance with the change in the differential polarity. In addition, logarithmic transformation processing and integration processing are performed so that the change over time of the target signal always passes a certain threshold such as the baseline when the extracted target signal transitions from peak to valley or from valley to peak. As a result, the target signal can be reliably discriminated based on the threshold value.

  According to the signal extraction circuit having the above configuration, the amplifier that amplifies the signal input through the capacitor reduces the amplification factor when the amplitude of the input signal is large, and increases the amplification factor when the amplitude of the input signal is small. The input signal is logarithmically converted by increasing the value. Therefore, when a modulated wave in which a minute signal component is superimposed on a carrier wave is input through the capacitor, a large differential waveform generated at the discontinuous point of the carrier wave is suppressed by the differentiation process by the capacitor, while being superimposed on the carrier wave. Only the small signal component thus amplified is amplified with a large amplification factor. Accordingly, it is possible to effectively amplify and extract a minute signal component superimposed on the carrier wave by suppressing (removing) the carrier wave component.

  Incidentally, for example, as shown in FIG. 9B, the normal output in the differentiation circuit also saturates a minute signal component when the operational amplifier is saturated. Therefore, only the minute signal component superimposed on the carrier wave is amplified. Cannot be extracted. However, according to the signal extraction circuit (carrier wave removal circuit) according to the present invention having the above-described configuration, it is possible to suppress only the output of a large differential waveform generated at the discontinuity point of the carrier wave. It can be amplified and extracted effectively.

The differential circuit described above is an operational amplifier that is the main component of the differential circuit, and impedance control means that is connected in parallel between the input terminal and the output terminal of the operational amplifier so that the impedance changes according to the level of the input signal to the input terminal. Specifically, the impedance control means has an exponential change characteristic such that the impedance increases when the input signal level is small, and the impedance decreases when the signal level is large. an amplifier having a logarithmic conversion characteristic can be constructed easily. In particular, when the impedance control means is realized by a pair of diodes connected in antiparallel, the impedance becomes substantially infinite for a minute input signal, and substantially zero [0 for an input signal with a large amplitude. Therefore, logarithmic conversion characteristics can be easily provided.

Hereinafter, a signal extraction method and a signal extraction circuit according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a processing concept of a signal extraction method according to the present invention. In this signal extraction method, as shown in FIG. 1, a modulated wave in which a target signal is superimposed on a carrier wave is subjected to differential processing, and then the differential waveform is subjected to logarithmic conversion processing and integration processing to thereby output a signal component related to the target signal as its output. It is implemented by obtaining. As will be described later, the differentiation process is performed using, for example, a capacitor. The logarithmic conversion process and the integration process are performed using an amplifier having logarithmic conversion characteristics.

  Incidentally, the modulation wave V (t) to be processed is obtained by superimposing a minute target signal on a carrier wave such as a rectangular wave or a triangular wave. In particular, the carrier wave has a lower fundamental frequency component than the target signal, and The signal includes a differential value (absolute value) larger than that of the target signal or a signal including an amplitude larger than that of the target signal. Note that a carrier wave including a differential value (absolute value) larger than the target signal means that the carrier wave and the target signal are temporally differentiated and compared for at least one period of the carrier wave. It means that the maximum value of the differential value (absolute value) of the carrier wave is larger than the maximum value of the differential value (absolute value) of the target signal. In addition, a carrier wave having an amplitude larger than that of the target signal means that when the carrier wave and the target signal are compared for at least one period of the carrier wave, the maximum value of the carrier wave amplitude within that period is the amplitude of the target signal. Means greater than the maximum value.

Further, the logarithmic conversion process and the integration process described above are executed simultaneously with the function of the integrating circuit dominant in the high resistance region where the self impedance is high and the logarithmic conversion function dominant in the low resistance region where the self impedance is low . The signal component related to the target signal obtained as the output of the signal extraction processing not only indicates the target signal itself, but also a part of information of the target signal, specifically, the timing at which the target signal crosses the threshold and its change The direction information is shown.

Now, the signal extraction circuit for executing the above-described signal processing method is schematically shown, for example, in such a manner that the input signal Vin is first-order differentiated using a one-stage differentiation circuit 10 as shown in FIG. As shown in FIG. 2, the input signal Vin is second-order differentiated by a two-stage differentiating circuit in which two differentiating circuits 10 and 20 are connected in series. In particular, each of the differentiating circuits 10 and 20 is composed mainly of an operational amplifier (op-amp) OP. Basically, the input signal Vin (Vin ′) is differentiated to input the inverting input of the operational amplifier OP. A capacitor Cin (differential processing function) leading to the terminal IN ⁻ , and a logarithmic conversion processing function and an integration processing function are connected in parallel between the inverting input terminal IN ⁻ of the operational amplifier OP and its output terminal. And an impedance control means Z provided with. Note that the operational amplifier OP mentioned here is generally popular, and is a differential amplifier having an inverting input terminal, a non-inverting input terminal, an output terminal, and a power supply input terminal, and has both an input impedance and a bare amplification factor. It has the characteristic of being extremely large.

  Here, a signal extraction circuit for removing a carrier wave (micro signal extraction circuit) that performs two-order differentiation by connecting two differentiating circuits 10 and 20 shown in FIG. 3 in series will be described as an example. As shown, even a signal extraction circuit that performs first-order differentiation using the differentiating circuit 10 (20) alone functions similarly. In addition, as described above, the modulated wave to be processed by the minute signal extraction circuit has a signal component (target signal) superimposed on a carrier wave (rectangular wave, triangular wave, sine wave) having an amplitude larger than the fluctuation range of the signal component as described above. The signal, or a differential component of the carrier wave (rectangular wave, sine wave) whose differential component is larger than the signal component, or a signal (combined wave) obtained by synthesizing these signals. The signal extraction circuit realized by the differentiation circuit 10 (20) inputs a modulated wave in which a minute signal component is superimposed on a carrier wave such as a rectangular wave, a triangular wave, or a sine wave, and reduces the influence of the carrier wave from the modulated wave. Thus, it plays a role of efficiently extracting minute signal components.

Specifically, the differentiating circuit 10 (20) differentiates the input signal Vin (Vin ′) at the inverting input terminal IN ⁻ of the operational amplifier OP through a series circuit of the input resistor Rin and the capacitor Cin. The reference voltage Vref for defining the operation reference level in the operational amplifier OP is input to the non-inverting input terminal IN ⁺ of the operational amplifier OP via the resistor Rref. The inverting input terminal IN of the operational amplifier OP ^- and its feedback circuit formed by the parallel-connected impedance control unit Z between the output terminal OUT, and is differentiated through the capacitor Cin of the input signal Vin (Vin ') The received signal is amplified with an amplification factor corresponding to the amplitude and output.

  Incidentally, the impedance control means Z is realized here by a pair of diodes D1, D2 connected in reverse parallel and a high frequency noise removing capacitor Cnc. Each of the diodes D1 and D2 is a general silicon diode having a characteristic that its impedance decreases exponentially in accordance with a forward current value. The reason why the polarities are reversed is that they are connected in parallel in order to cope with currents in both directions. The capacitance of the high-frequency noise removing capacitor Ccn is determined so that only noise having a frequency higher than that of the target signal is fed back. When considering the feedback impedance related to the modulated wave, its existence may be substantially ignored. it can. However, the capacitance of the high frequency noise removing capacitor Cnc affects the time constant governing the convergence of the output to the baseline.

  This impedance control means Z is such that the amplitude of the differential component of the input signal Vin (Vin ′) input after being differentially processed through the capacitor Cin is small, and the impedance of the diodes D1 and D2 is high when the current flowing therethrough is small. Therefore, the amplification factor for the input signal Vin (Vin ′) by the operational amplifier OP is increased by setting the impedance large. On the contrary, when the amplitude of the differential component is large and the current flowing therethrough is large, the impedances of the diodes D1 and D2 are exponentially lowered. Therefore, the impedance is set small and the input signal Vin (Vin ') is amplified. Reduce the rate. Therefore, the impedance control means Z plays a role of providing logarithmic conversion characteristics to the operational amplifier OP by changing the impedance according to the amplitude of the differential component of the input signal Vin (Vin ′).

  In particular, the impedance control means Z increases the impedance of the operational amplifier OP because the impedance increases when the amplitude (voltage) of the differential component of the input signal Vin (Vin ′) is less than the forward bias voltage VL of the diodes D1 and D2. The ratio is set to be large so that the operational amplifier OP functions as a normal linear amplifier. When the amplitude (voltage) of the differential component of the input signal Vin (Vin ') exceeds the forward bias voltage VL of the diodes D1 and D2, the impedance of the impedance control means Z decreases exponentially, so the operational amplifier OP Thus, the operational amplifier OP substantially functions as a comparator. As a result, the operational amplifier OP has logarithmic conversion characteristics.

  Further, the high frequency noise removing capacitor Cnc exhibits an action of integrating the input signal Vin (Vin ′) by accumulating charges according to the potential difference between the input signal Vin (Vin ′) and the inverted output from the operational amplifier OP. . The logarithmic conversion characteristic and the integration function given to the operational amplifier OP by the impedance control means Z work simultaneously. However, since the amplification factor of the operational amplifier OP becomes large when the amplitude of the differential component of the input signal Vin (Vin ′) is small as described above, the logarithmic conversion function becomes dominant as compared with the integration function by the capacitor Cnc, and vice versa. In addition, when the amplitude of the differential component of the input signal Vin (Vin ′) is large, the amplification factor becomes small, so that the integration function by the capacitor Cnc becomes dominant.

According to the differentiation circuit 10 (20) having the above-described configuration, the input signal Vin (Vin ′) differentiated through the capacitor Cin is applied to the inverting input terminal IN ⁻ of the operational amplifier OP, so that the input signal Vin (Vin ′) ), A large differential waveform generated at the discontinuity can be suppressed. Accordingly, only the component of the target signal superimposed on the carrier wave is applied exclusively to the inverting input terminal IN ⁻ of the operational amplifier OP. In the operational amplifier OP to which the differential component of the input signal Vin (Vin ′) is input, the target signal is amplified with a large amplification factor when the amplitude of the target signal is small, and the amplification factor is increased when the amplitude of the target signal increases. The charge corresponding to the target signal is reduced and accumulated in the capacitor Cnc (integration effect by charging the capacitor Cnc).

  At this time, the carrier wave and the target signal wave are subjected to the same handling, and the output reaches the vicinity of the baseline even with a slight change. Further, when the differential value by the capacitor Cin is large, the impedance of the impedance control means Z becomes small as described above, so that the output is restricted at the discontinuous point of the carrier wave. However, since the operational amplifier OP itself does not saturate, the signal is not destroyed.

  Therefore, as shown in FIG. 4A, when a modulated wave Vin in which a minute signal component (target signal) is superimposed on a rectangular wave is input, the output of the differentiating circuit 10 (20) is as shown in FIG. 4B. In the operational range of the operational amplifier OP (power supply voltage: -Vd to + Vd), the operation amplifier OP greatly changes. In particular, when the amplitude of the target signal is small, the signal is amplified with a large amplification factor under the above-described logarithmic conversion characteristics, and the output signal changes to the level of approximately power supply voltage ± Vd with reference to the baseline (0 V). When the amplitude of the target signal is increased, the amplification factor is suppressed to a small value, so that a voltage change corresponding to the amount of charge (integrated value) accumulated in the capacitor Cnc is exhibited. Since the capacitor Cnc gradually accumulates electric charges as the target signal is repeatedly changed, the logarithmic conversion characteristic functions accordingly, and there is a region (voltage range) in which the target signal is amplified with a large amplification factor. Reduce gradually.

  Therefore, according to the signal extracting circuit for removing a carrier wave configured and functioning as described above, when the input signal Vin composed of the modulated wave V (t) in which a minute signal component is superimposed on the carrier wave, the input signal Vin is Differentiating processing is performed by the differentiating circuit 10 in the preceding stage, the carrier wave component is suppressed, and the signal component is amplified and output (first-order differentiation processing). The output signal of the differentiating circuit 10 is input to the subsequent differentiating circuit 20 and subjected to differential processing in the same manner. Further, the carrier wave component is suppressed and the signal component is further amplified and output (second-order differential processing). . As a result, when the carrier wave is a rectangular wave, for example, as shown in FIG. 5A, the first-order differential waveform and the second-order differential waveform are obtained, the carrier wave component in the input signal Vin is removed, and the signal The component is amplified and output.

  When the carrier wave is a triangular wave, for example, as shown in FIG. 5B, the first-order differential waveform and the second-order differential waveform are obtained, and the carrier wave component in the input signal Vin is the same as in the case of the rectangular wave. Then, the signal component is amplified and output. Further, when the carrier wave is a sine wave, for example, as shown in FIG. 5C, the first-order differential waveform and the second-order differential waveform are obtained, and the input signal Vin is the same as in the case of the rectangular wave or the triangular wave described above. Is removed and the signal component is amplified and output.

  That is, according to the signal extraction circuit for removing a carrier wave according to the present invention, the impedance control circuit Z realized by a pair of diodes D1, D2 and the like connected in anti-parallel, the differentiation circuit 10, mainly the operational amplifier OP, Since the amplification factor of 20 is changed according to the input signal level, the fluctuation range of the amplified output from the differentiation circuits 10 and 20 is limited, and the time constant when the high frequency noise removing capacitor Cnc is discharged is increased. Can do. Therefore, regardless of the differential value of the carrier wave, it is possible to efficiently amplify and extract only a minute signal component superimposed on the carrier wave and effectively remove the carrier wave component. In other words, the output change when the absolute value of the differential value of the carrier wave is small can be suppressed by increasing the time constant when the high frequency noise removing capacitor Cnc is discharged. In particular, as compared with the signal processing waveforms (first-order differential waveform, second-order differential waveform) by the conventional circuits shown in FIGS. 10 (a), 10 (b), and 10 (c), the signal extraction circuit having the above-described configuration is more apparent. Therefore, it can be said that the carrier wave removal effect is very good because the component of the carrier wave can be made substantially zero (0) by the second-order differentiation process.

  When a general differentiation circuit is used, the differential order necessary for removing the carrier wave is determined solely by the shape of the carrier wave. In this respect, in the signal extraction circuit according to the present invention, the order of differentiation of the input signal (modulated wave) depends mainly on the magnitude of the signal component. Moreover, the main purpose of this signal extraction circuit is to amplify a minute signal component included in the modulated wave by fully utilizing its logarithmic conversion characteristics. Accordingly, when the amplitude of the signal component superimposed on the carrier wave is large and the logarithmic transformation is sufficiently performed by the first-order differentiation, the first-order differentiation process is sufficient. Conversely, if the amplitude of the signal component is small, the differential circuit is connected in series in multiple stages so as to repeatedly execute the second-order differentiation and third-order differentiation and the differentiation process until an output with sufficient logarithmic transformation is obtained. A signal extraction circuit may be constructed. Further, even if the differentiation process is repeated more than necessary, the output signal obtained by this is only compressed at the top and bottom by logarithmic transformation, so that there is almost no problem in the subsequent digital processing of the output signal.

  Further, in the signal extraction circuit described above, the differential component (bending) of the carrier wave larger than the signal component appears in the output signal as one pulse and cannot be distinguished from the output signal based on the target signal. In this respect, the carrier component is not completely removed, but if the number of pulses of the output signal based on the target signal is large, the influence can be substantially ignored. Therefore, if the signal extraction circuit having the above-described configuration is used, for example, a minute signal component superimposed on a carrier wave can be analyzed without using a digital processing technique such as fast Fourier transform. Therefore, the present invention is very effective in realizing a sensor device with a simple configuration by applying to sensing processing such as distance measurement using the self-coupling effect of the laser beam described above. Further, since the carrier wave removal circuit having the above-described configuration can be easily integrated, it is effective for use as a sensing amplifier integrated with a sensing element.

  The present invention is not limited to the embodiment described above. For example, the pair of diodes D1 and D2 described above may be realized as PN junctions that are simultaneously integrated in a semiconductor integrated circuit that constructs the operational amplifier OP. It is also possible to construct a variable impedance nonlinear resistance circuit as the impedance control means Z using a transistor or the like. It is of course possible to stabilize the operation by connecting in parallel between the input and output terminals of the operational amplifier OP, a high value resistor that does not impair the function of the impedance control means Z. Further, when the carrier wave component is removed by an ordinary differentiating circuit, second order differentiation is required when the carrier wave is a triangular wave, and first order differentiation is required when the carrier wave is a rectangular wave or a sine wave. Even in the carrier wave removal circuit, the differential processing rank may be determined in accordance with the signal size regardless of the shape of the carrier wave.

  When differentiating circuits are connected in multiple stages, an amplification limiting resistor may be provided in parallel with the diodes D1 and D2 in the subsequent differentiating circuit in order to eliminate noise. By the way, when there is no resistance, there is a possibility that noise will be greatly amplified and become indistinguishable from the signal, but by inserting a resistance, the amplification factor of the operational amplifier OP is limited, so that noise and signal can be easily distinguished. become.

  Further, since the feedback circuit of the operational amplifier OP is composed of the diodes D1 and D2, the operational amplifier OP has a function equivalent to that of the bidirectional peak hold circuit. Therefore, since the peak hold function can be regarded as an almost integral operation, even if the above-described noise removing capacitor Cnc is omitted, the integration function can be substantially provided. In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.

An application example suitable for using the present invention described above will now be described.
One of optical distance measurement techniques uses a self-coupling effect (also referred to as a self-mixing effect) of laser light (for example, Japanese Patent Laid-Open Nos. 10-246782 and 11-287859). See the publication). In this method, for example, as shown in FIG. 6, a laser element (hereinafter referred to as LD) 1 driven by using a predetermined modulation signal irradiates a measurement object 2 with laser light, and is reflected by the measurement object 2 to reflect the above-mentioned The modulated light (modulated wave) generated by the self-coupling of the reflected laser light returning to the laser element 1 and the output laser light is received by a light receiver (hereinafter referred to as PD) 3, and the output is subjected to frequency analysis or the like. The distance L to the measurement object 2 is measured.

  That is, when the oscillation wavelength of the laser beam emitted from the laser element 1 is changed, the return laser beam reflected by the measurement object 2 at a certain oscillation wavelength and the output laser beam of the laser element 1 satisfy the resonance condition. (Self-coupling effect), the output of the light receiver 3 increases. For example, for a type of laser element in which the oscillation wavelength of the laser light changes in accordance with the applied current value, a triangular wave α as shown in FIG. Wavelength modulation can be performed. That is, when looking at one period of the triangular wave α, the current value continuously increases with the passage of time, so the wavelength of the emitted laser light continuously increases accordingly, and the current value reached a peak. After that, since the current value continuously decreases, the wavelength of the emitted laser light correspondingly decreases accordingly. As the wavelength of the emitted laser beam continuously increases and decreases in this manner, the resonance condition with the return laser beam is satisfied many times. As a result, the light receiving device 3 causes a minute resonance in the triangular wave α. A beat waveform (modulated wave) β in which components are superimposed is obtained. Therefore, if this beat waveform β is analyzed, the distance L from the frequency of the resonance component to the measurement object 2 can be obtained.

  The public literature that introduced this measurement technology includes the 1994 Annual Conference of the Tokai Branch Joint Conference on Electrical Engineering, 1994-10-6, No.650, “Distance Meter Using Self-Coupling Effect of Semiconductor Laser”, Ueda, Yamada, Shito, and Queensland University, Australia, “Distance Measurement Using External Optical Feedback in a Vertical-Cavity Surface-Emitting Laser” Student; Garth Niethe, Supervisor; Dr Aleksandar D. Rakic, HYPERLINK "http: //innovexpo.itee .uq.edu.au / 2000 / 348657979.htm "http://innovexpo.itee.uq.edu.au/2000/348657979.htm.

  That is, when looking at one period of the triangular wave α, the current value continuously increases as time passes, and accordingly, the intensity of the laser light emitted from the laser element 1 also increases continuously. Then, since the current value continuously decreases after the current value reaches the peak, the intensity of the laser beam emitted from the laser element 1 is also continuously decreased accordingly. At this time, the wavelength of the laser beam emitted from the laser element 1 expands and contracts according to the increase / decrease of the current value. As the intensity of the emitted laser beam continuously increases and decreases in this way, the resonance condition with the return laser beam is satisfied many times. As a result, the intensity (amplitude) changes due to resonance as described above. A minute component (target signal) is superimposed on the intensity (carrier wave) of the continuous laser beam.

  Accordingly, when analyzing a beat waveform (modulated wave) β obtained by superimposing a minute resonance component (target signal) on a carrier wave having a large amplitude such as a triangular wave α, which is obtained from the laser light described above, a fast Fourier transform (FFT) or the like is used. Instead of digital processing, the frequency of the target signal can be obtained by extracting the target signal using the present invention and counting the output with a counter. Accordingly, the distance L from the laser element 1 to the measurement object 2 can be measured by analyzing the frequency of the target signal.

The figure which shows the processing concept of the signal extraction method which concerns on this invention. The figure which shows the structural example of the signal extraction circuit (1st-order differentiation process) which concerns on one Embodiment of this invention. The figure which shows the structural example of the signal extraction circuit (2nd-order differentiation process) which concerns on another embodiment of this invention. The figure which shows the example of the differential output waveform of the modulation wave by the signal processing circuit shown in FIG. The figure which shows the example of the input modulation wave by the signal processing circuit which concerns on this invention, its 1st-order differentiation processing waveform, and 2nd-order differentiation processing waveform. The figure which shows the schematic structural example of the distance meter using the self-coupling effect of a laser beam. The figure which shows the example of the frequency modulation signal (carrier wave) with respect to a laser beam, and the beat waveform (modulation wave) of the laser beam produced by the self-coupling effect. The figure which shows the example of a conventional general differentiation circuit. The figure which shows the example of the differential output waveform of the modulation wave by the differentiating circuit shown in FIG. The figure which shows the example of the input modulation wave by the conventional general differentiation circuit, its 1st-order differentiation processing waveform, and 2nd-order differentiation processing waveform. The figure which shows another example of the conventional differentiation circuit to which a well-known technique is applied. The figure which shows the example of the differential output waveform of the differentiating circuit shown in FIG.

Explanation of symbols

10,20 Differentiation circuit OP Operational amplifier Cin Differentiation capacitor Cnc High frequency noise elimination capacitor Rin Input resistance D1, D2 Diode (feedback circuit; impedance control means)

Claims (9)

The signal component of the target signal is derived from a modulated wave having a fundamental frequency component lower than that of the target signal and having a differential value larger than the target signal or a carrier wave including an amplitude larger than the target signal. When extracting
After differentiating the modulated wave, with when obtained differential value is large to dominate the logarithmic conversion function, wherein when the differential value is small and the logarithmic conversion process on the differential value in the dominant integral function A signal extraction method characterized by performing integration processing simultaneously . The logarithmic conversion process and the integration process, temporal change of the target signal to be extracted, when the extracted target signal transitions valley peak or from trough, to the mountain, as always to pass a certain threshold The signal extraction method according to claim 1, wherein the signal extraction method is executed. While performing the differentiation process using a capacitor,
3. The signal extraction according to claim 1, wherein the logarithmic conversion process and the integration process are performed using a feedback amplifier that determines a feedback impedance by using at least a pair of semiconductor junctions connected in antiparallel. Method.   4. The signal extraction method according to claim 1, wherein the extracted signal is regarded as a modulated wave and the signal extraction method according to claim 1 is repeated a plurality of times. The signal component of the target signal is derived from a modulated wave having a fundamental frequency component lower than that of the target signal and having a differential value larger than the target signal or a carrier wave including an amplitude larger than the target signal. A signal extraction circuit for extracting,
An amplifier that has a signal input terminal and a reference input terminal, amplifies and outputs the modulated wave input through the capacitor, and feedback means that feeds back the output of the amplifier to the signal input terminal of the amplifier,
The feedback means changes its impedance exponentially so that the impedance increases when the voltage between the input and output of the amplifier is small, and the impedance increases when the voltage between the input and output of the amplifier is large. A signal extraction circuit characterized by being.   6. The signal extraction circuit according to claim 5, wherein the feedback means is a pair of semiconductor junctions connected in antiparallel.   The amplifier operates substantially as an operational amplifier when the voltage between its input / output terminals is smaller than the conduction voltage of a pair of semiconductor junctions connected in reverse parallel as the feedback means, and the voltage between the input / output terminals is 6. The signal extraction circuit according to claim 5, wherein the signal extraction circuit substantially operates as a comparator when the conduction voltage is higher than the semiconductor junction.   8. The signal extraction according to claim 5, wherein the feedback means in the feedback operational amplifier comprises only a pair of semiconductor junctions connected in antiparallel and a high-frequency removing capacitor connected in parallel to these semiconductor junctions. circuit.   9. A signal extraction circuit, wherein the signal extraction circuit according to claim 5 is used as one structural unit, and a plurality of structural units are connected in multiple stages.

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