WO2022004639A1 - Detection circuit - Google Patents

Abstract

Provided is a detection circuit including: a current mirror circuit that copies an input sensor signal to output a first input signal and a second input signal in parallel; a waveform shaping circuit that outputs, when the first input signal is input thereto, an adjustment signal in which a voltage variation with respect to elapsed time is adjusted so as to follow a set reference variation; a voltage comparator that compares the voltage value of the adjustment signal and a reference voltage value and that outputs a first comparison signal; a current comparator that compares the current value of the second input signal and a reference current value and that outputs a second comparison signal; and a logical operation circuit that performs a logical operation on the first comparison signal and the second comparison signal and that outputs a detection signal that continues from a start point in time of the second comparison signal to an end point in time of the first comparison signal. According to this detection circuit, it is possible to suppress the influence of time walk while ensuring linearity of the peak value and time width.

Description

Detection circuit

The present invention relates to a detection circuit that detects a sensor signal.

The Time-over-Threshold method (ToT method) is known as a sensor signal detection method (see, for example, Patent Document 1). The ToT detection circuit that employs the ToT method measures a time width that exceeds a set threshold value for an input sensor signal. When the sensor signal is a short-time width current pulse signal, the adjustment signal passed through the primary semi-Gaussian waveform shaping circuit is input to the ToT detection circuit. If the time width is measured in this way, the peak value of the adjustment signal can be measured from the measured time width without using an ADC (Analog-to-Digital Converter). The peak value of the adjustment signal can be used to estimate the amount of signal captured by the sensor. Since the ToT detection circuit does not need to mount an ADC, it can be realized relatively simply and on a small scale.

Japanese Patent No. 5531021

According to the conventional ToT method, when the sensor signal is a short-time width current pulse signal, the detected time width is determined by the peak value of the adjustment signal adjusted through the semi-Gaussian waveform shaping circuit and the non-linearity of the time width. The process of converting to a peak value was complicated. Further, there is also a problem of a time walk in which a difference in the rise of the signal occurs due to a difference in the wave height of the adjustment signal, and the time until the adjustment signal reaches the threshold value varies.

The present invention has been made to solve such a problem, and provides a detection circuit that suppresses the influence of the time walk while ensuring the line formation of the peak value and the time width.

The detection circuit according to one aspect of the present invention includes a current mirror circuit that copies an input sensor signal and outputs the first input signal and the second input signal in parallel, and a voltage with respect to the elapsed time when the first input signal is input. A waveform shaping circuit that adjusts the fluctuation according to the set reference fluctuation and outputs the adjustment signal, a voltage comparator that compares the voltage value of the adjustment signal with the reference voltage value, and outputs the first comparison signal, and the second. From the start of the second comparison signal, the current comparator that compares the current value of the input signal with the reference current value and outputs the second comparison signal, and the first comparison signal and the second comparison signal are subjected to logical calculations. It is provided with a logic calculation circuit that outputs a detection signal that continues until the end of the first comparison signal.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a detection circuit that suppresses the influence of the time walk while ensuring the line formation of the peak value and the time width. It was

It is a graph which shows the waveform example of the sensor signal handled in this embodiment. An example of an output waveform obtained when inputting to a first-order semi-Gaussian waveform shaping circuit generally used in the prior art is shown. It is a graph which enlarged the rising area of the graph of FIG. It is a circuit diagram which shows the whole structure of the detection circuit which concerns on this embodiment. This is a specific circuit example of the current mirror circuit. This is a specific circuit example of a waveform shaping circuit. It is a graph which shows the waveform example of the adjustment signal which is an output signal of a waveform shaping circuit. This is a specific circuit example of a slew rate limiting resistor circuit. This is a concrete circuit example of a one-shot circuit. It is a figure which shows the specific example of the input waveform and the output waveform of a logic operation circuit. It is a graph which shows the correlation of a crest value and a time width. This is an example of the detection result in the conventional ToT detection circuit. It is an example of the detection result in one Example of the detection circuit which concerns on this embodiment.

Hereinafter, the present invention will be described through embodiments of the invention, but the invention according to the claims is not limited to the following embodiments. Moreover, not all of the configurations described in the embodiments are indispensable as means for solving the problem.

Figure 1 is a graph showing an example of the waveform of the sensor signal S _in handled in this embodiment. The sensor signal S _in is, for example, a short-time width current pulse signal which is an output signal of a photodetector for detecting scintillation light. The horizontal axis shows the elapsed time, and the vertical axis shows the current value of the sensor signal. Here, as the sensor signal S _in , three examples of the signals S _a , S _b , and S _c are shown. Each sensor signal indicates a peak current value corresponding to the signal amount q detected by the sensor. Specifically, the peak current value of the signal S _a is proportional to the amount of signal q _a, the peak current value of the signal S _b is proportional to the signal amount q _{b (>} q _a), the peak of the signal S _c current The value is proportional to the _{signal amount q c} (> q _b).

_{FIG. 2 shows an example of an output waveform obtained when the sensor signals (signals S a} , S _b , S _c ) shown in FIG. 1 are input to a first-order semi-Gaussian waveform shaping circuit generally used in the prior art. Is shown. In the present embodiment, the signal output by the waveform shaping circuit is referred to as an "adjustment signal". In the figure, the horizontal axis shows the elapsed time, and the vertical axis shows the voltage value of the adjustment signal. Signals _{S a, S b, S c,} by passing through the semi-Gaussian waveform shaping circuit, the adjustment signal _S ra having a waveform defined by the time constant with the shaping circuit _itself, is converted S _rb, the _{S rc} ..

Peak value is a peak value of the adjustment signal _{S ra} is _{h a,} the peak value of the adjustment signal _{S rb} is _h b a (> _{h a),} the peak value of the adjustment signal _{S rc} is _h c _{(> h} b) Is. These peak values h _a , h _b , and h _c are proportional to the signal amount q _a , the signal amount q _b , and the signal amount q _c. Further, as shown in the figure, the adjustment signal has a property that the signal having a larger peak value h rises sharper.

_Assuming that the threshold value V th is set and the _{duration exceeding} the threshold value V th is the time width of each signal, the time width of the adjustment signal S _{ra is t wa} and the time width of the adjustment signal S _rb is t _wb (. > T _wa ), and the time width of the _{adjustment signal S rc is t wc} (> t _wb ). As can be understood from the figure _{, the linearity of the time width measured simply separated by the threshold value Vth} is not guaranteed with respect to the peak value. That is, the amount of change in the time width with respect to the amount of change in the peak value is not constant. If the linearity of the time width with respect to the crest value is not guaranteed, even if the time width is detected by the detection circuit, the post-processing for converting the time width to the crest value becomes complicated and requires a large amount of processing time. Will end up.

FIG. 3 is a graph in which the rising region of the graph of FIG. 2 is enlarged. Even if the timing at which the adjustment signals rise is the same, the time required for _{each adjustment signal to reach the threshold value Vth} differs due to the property that the adjustment signal with a larger peak value rises steeper. The timings at which the illustrated adjustment signals S _ra , S _rb , and S _rc rise are the same, but for example, _{the time until the adjustment signal S ra} reaches the threshold value V _th and the adjustment signal S _rc reach the threshold value V _th. During the time until, a so-called time walk occurs, as shown by the double-headed arrow. The occurrence of time walk is an obstacle in order to accurately detect the occurrence timing of the sensor signal S _in.

The detection circuit according to the present embodiment corresponds to such a problem, and is a detection circuit that suppresses the influence of the time walk while ensuring the line formation of the peak value and the time width. FIG. 4 is a circuit diagram showing the overall configuration of the detection circuit 100 according to the present embodiment. The detection circuit 100 is mainly composed of a current mirror circuit 110, a waveform shaping circuit 120, a voltage comparator 130, a current comparator 140, a one-shot circuit 150, and a logic operation circuit 160.

In the present embodiment, the detection circuit 100 is a circuit that detects a short-time width current pulse signal as a sensor signal, and outputs a pulse signal having a time width corresponding to the input sensor signal. The current mirror circuit 110 _{copies the input sensor signal S in} and outputs the first input signal S _m1 and the second input signal S _m2 in parallel. When the first input signal S _m1 is input, the waveform shaping circuit 120 adjusts the voltage fluctuation with respect to the elapsed time so as to be in line with the set reference fluctuation, and outputs the _{adjustment signal S r1.} The voltage comparator 130 compares the voltage value V _{r1 of the adjustment signal S r1} with the reference voltage value V _th , and outputs the first comparison signal _Sc1.

The current comparator 140 compares the current value I _{m2 of the second input signal S m2} with the reference current value I _th , and outputs the second comparison signal S _c2. One-shot circuit 150 generates and outputs an extension signal S _p2 obtained by extending the signal duration of the second comparison signal S _c2 input. The logical operation circuit 160 performs a logical operation on the first comparison signal S _c1 , the second comparison signal S _c2, and the extension signal S _p2 , and performs a logical operation on the first comparison signal S _{c1 from the start time of the second comparison signal S c2} . _{The detection signal S out} that continues until the end point is output. The specific actions of each element will be described below in sequence.

FIG. 5 is a specific circuit example of the current mirror circuit 110. _{When the sensor signal S in} is input to the IN terminal, the current mirror circuit 110 _{copies the sensor signal S in} and parallels the first input signal S _m1 from the OUT 1 terminal and the second input signal S _{m 2 from the OUT 2 terminal.} And output. The current mirror circuit 110 also functions as a current buffer circuit, and adjusts the current ratios of the first input signal S _m1 and the second input signal S _{m2 to the sensor signal S in.}

Assuming that the current values of the sensor signal S _{in are I in} and the current values of the first input signal S _m1 and the second input signal S _m2 are I _m1 and I _m2 , respectively, I _m1 = α × I _in and I _m2 = β ×. Expressed as I _in . That is, the current ratio of the first input signal S _m1 to the sensor signal S _in is alpha, the current ratio of the second input signal S _{m @ 2} to the sensor signal S _in is adjusted to beta. Specifically, three FETs (Field Effect Transistors) to which the gates of each other are connected are selected and adopted so that the channel width of each FET is 1: α: β. Since the first input signal S _m1 is then input to the voltage comparator 130 via the waveform shaping circuit 120, a large current is not required, and the second input signal S _m2 is then input to the current comparator 140, so that it is relatively relatively. It is convenient to have a large current. Therefore, in this embodiment, it is set so that 1>β> α.

FIG. 6 is a specific circuit example of the waveform shaping circuit 120. As described above, the use of primary semi Gaussian waveform shaping circuit used generally so far, as shown in FIG. 2, the peak value varies in proportion to the signal amount of the sensor signal S _in However, if the peak values were different from each other, the amount of change in the voltage value with the passage of time was also different. Therefore, the linearity of the time width with respect to the crest value was lost. Therefore, in the present embodiment, a slew rate limiting type waveform shaping circuit is adopted as the waveform shaping circuit 120.

When the first input signal S _m1 is input, the waveform shaping circuit 120 adjusts the voltage fluctuation with respect to the elapsed time so as to be in line with the set reference fluctuation, and outputs the _{adjustment signal S r1.} The reference fluctuation is set as a voltage fluctuation in which the amount of change in the voltage value with respect to the passage of time at the time of rising and the amount of change in the voltage value with respect to the passage of time at the time of falling are constant. Specifically, the waveform shaping circuit 120 is mainly composed of an operational amplifier, a capacitor, and a slew rate limiting resistance circuit 121 as shown in the figure, and the reference variation is determined by the circuit configuration of the slew rate limiting resistance circuit 121.

FIG. 7 is a graph showing a waveform example _{of the adjustment signal Sr1} , which is an output signal of the waveform shaping circuit 120. Similar to the graph of FIG. 2, the horizontal axis shows the elapsed time, and the vertical axis shows the voltage value of the sensor signal. Here, assuming the first input signal a first input signal _{S m1} as the signal _S a shown in FIG. 1 to be input to the waveform shaping circuit _120, S b, _{S c} is copied by the current mirror circuit 110, these signal output, respectively S _'ra, S' _rb, and S _'rc.

Signal S 'peak value of _ra is _{h a,} the signal S' peak value of _rb is _{h b,} the peak value of the signal S _'rc is _{h c.} Signal _{S 'ra, S' rb,} S ' variation of the voltage value over time when the rise of _rc is adjusted to either substantially equal, likewise, the voltage value over time at the fall The amount of change is also adjusted so that they are almost equal. In other words, the signal _{S 'ra, S' rb,} S 'rc varies almost linearly even when the rise time is also falling, the slope also coincide approximately with one another.

When set threshold V _th in which duration exceeds the a and duration of each signal, the signal S 'duration of _ra is t' is _wa, 'the time width of _rb t' signal S _{wb (>} t 'is a _wa), signal S' is the duration of the _rc is _{t 'wc (>t' wb} ). Signal _{S 'ra, S' rb,} S 'rc , as described above, changes almost linearly even when the rise time is also falling, since the slope also coincide approximately with each other, the detected time width t ' _W shows good linearity with respect to the peak value h. That is, the amount of change in the time width with respect to the amount of change in the crest value is almost constant, and the time width is proportional to the crest value.

FIG. 8 is a specific circuit example of the slew rate limiting resistance circuit 121. The slew rate limiting resistor circuit 121 contributes to the setting of the reference variation that determines the circuit characteristics of the waveform shaping circuit 120. Specifically, depending on how the slew rate limiting resistance circuit 121 is configured, _{it is possible to adjust the inclination of the input first input signal S m1 at} the rising edge and the tilt at the falling edge.

As shown in the figure, the slew rate limiting resistance circuit 121 includes a change unit 122 that adjusts the gate voltage of two FETs to which the end of the resistance element R is connected to the source. The change unit 122 mainly has a variable resistor. The resistance value of the variable resistor may be adjusted by an operator at the time of manufacturing the detection circuit 100, or may be changed by, for example, a control signal from a control device. In the present embodiment, by adjusting the variable resistance of the changing unit 122, _{the inclination of the input first input signal S m1 at} the rising edge and the tilting at the falling edge are adjusted. These slopes are adjusted in consideration of the processing capacity per unit time (the number of sensor signals that can be processed in a unit time) required for the detection circuit 100, the stability of the circuit, and the like.

FIG. 9 is a specific circuit example of the one-shot circuit 150. _{When the second comparison signal Sc2} , which is a pulse signal output from the current comparator 140, is input to the one-shot circuit 150, the one-shot circuit 150 generates and outputs _{an extension signal Sp2 in} which the signal end time is extended while maintaining the signal start time. do. The one-shot circuit 150 is a circuit equivalent to a monostable multivibrator using a logic gate, and the extension time of the pulse signal is determined by the capacitance of the capacitor and the resistance value of the variable resistor included in the time adjustment unit 151. The resistance value of the variable resistor may be adjusted by an operator at the time of manufacturing the detection circuit 100, or may be changed by, for example, a control signal from a control device.

FIG. 10 is a diagram showing specific examples of the input waveform and the output waveform of the logical operation circuit 160. The logic operation circuit 160 in this embodiment is an OR logic gate having three input gates. The first comparison signal S _c1 , the second comparison signal S _c2 , and the extension signal S _p2 are input to the three input gates, respectively. 10 (a) shows the _{waveform of the first comparison signal S c1} , FIG. 10 (b) shows the waveform of the second comparison signal S _c2 , and FIG. 10 (c) shows the waveform of the extension signal S _p2 . The horizontal axis shows the elapsed time, and the vertical axis shows the signal level (High = 1, Low = 0).

First comparison signal _{S c1} is also possible to limit the slew rate wave-shaping circuit 120, slightly delayed rising relative time of occurrence _{t 0} of the signal, changes from Low to High is the time _{t 2} There is. And, High is continued until the time _{t 4.} The duration from time t ₂ to time t ₄ is proportional to the _peak value of the adjustment signal S r1 as described above.

The second comparison signal _Sc2 is an output signal of the current comparator 140. Since the current comparator 140 targets the current value that rises sharply at the same time as the signal is generated, the second comparison signal _Sc2 changes from Low to High at substantially the same time as the signal generation time t _0. However, since the current value rises sharply falls immediately without sustained, the second comparison signal S _c2 is changed from High to Low to before time t ₁ from time t _2.

The extension signal _Sp2 is an output signal of the one-shot circuit 150. The output wiring of the current comparator 140 is branched in the middle, one of which is connected to the input gate of the logical operation circuit 160 and the other of which is connected to the input terminal of the one-shot circuit 150. The extension signal S _p2 rises at approximately time t ₀ at the same time as the second comparison signal _Sc 2, and High continues until time t _{3 after time t 2.} In other words, the extension time by the one-shot circuit 150 is such that the time t _{3 is a time after the time t 2} which is the rising time of the first comparison signal S _{c1 and} the falling time of the first comparison signal S _c1 . it is adjusted to be the previous time from the time t ₄ is the time. _{The time t 4} referred to when adjusting the time t ₃ is the falling time of the first comparison signal S _{c1 when the minimum peak value of the adjustment signals S r1 that} can be the target is observed.

FIG. 10D shows the waveform _{of the detection signal S out} , which is the output signal of the logical operation circuit 160. Similar to FIGS. 10 (a) to 10 (c), the horizontal axis indicates the elapsed time, and the vertical axis indicates the signal level (High = 1, Low = 0).

As described above, since the logic operation circuit 160 in the present embodiment is an OR logic gate, at a certain time t, any one of the first comparison signal _Sc1 , the second comparison signal _Sc2 , and the extension signal _Sp2 is High. If so, the detection signal _Out is also High. On the other hand, if all of the first comparison signal S _c1 , the second comparison signal S _c2 , and the extension signal _{Sp 2} are Low, the detection signal S _out is Low.

The detection signal S _out changes from Low to High at approximately time t ₀ , and becomes a waveform in which _{the High state is continued until time t 4.} That is, the logic operation circuit 160 starts at time _{t 0,} and outputs a pulse signal having a time width Tw from time _{t 0} to time _{t 4.}

_{As described above, the adjustment signal S r1,} which is the output signal of the waveform shaping circuit 120, has a substantially constant time from the time of signal generation until the set threshold value _{Vth is reached (= t 0} to t) regardless of the peak value. It is adjusted to be _2). Therefore, if the time width of the first comparison signal S _c1 is proportional to the _{peak value of the adjustment signal S r1} , the time width Tw of _{the detection signal S out} is also proportional to the peak value of the adjustment signal S r1.

FIG. 11 is a graph showing the correlation between the peak value h of the adjustment signal S _r1 and the time width Tw of the detection signal S _out. The horizontal axis shows the peak value, and the vertical axis shows the time width. As shown in the figure, the time width Tw _{of the detection signal S out} is proportional to the _{peak value of the adjustment signal S r1.} Incidentally, the peak value _h a in _FIG, h b, _{h c} is the signal S _'ra, S' _rb shown in FIG. 6, a respective peak value in the three examples of S _'rc, the time width Tw _a , Tw _b and Tw _c are the time widths of the detection signals S _{out corresponding to each.}

_{If the detection signal S out} output by the detection circuit 100 is counted by a counter according to, for example, a clock signal input at a fixed cycle, the time width Tw can be converted into numerical data. Further, the converted numerical data can be immediately converted into the peak value h by using the linearity shown in FIG.

As described above, the peak value h of the adjustment signal _{S r1} is proportional to the signal amount q of the sensor signal _{S in.} Accordingly, terms have been peak value h can be converted into a signal quantity q of the input sensor signal S _in. Since it is not necessary to mount an ADC in such a detection circuit 100 and a digital processing device around it, it can be realized relatively simply and on a small scale. That is, the entire device can be constructed at low cost, and the number of sensor signals that can be processed per unit time can be increased.

As described above, the time width Tw of the detection signal S _out detection circuit 100 is output than equivalent to the time width t _'w adjusted by the waveform shaping circuit 120, showed good linearity with respect to the peak value h shows a good linearity with respect to the signal quantity q of turn sensor signal S _{in. Further, since the rise time of the detection signal S out} output by the detection circuit 100 is the rise time of the second comparison signal _Sc2 , it is almost unaffected by the time walk and is extremely close to the generation timing of the _{sensor signal S in.} .. _{That is, the processing device in the subsequent stage that processes the detection signal S out} output by the detection circuit 100 can analyze the generation timing and the signal amount of the sensor signal with high accuracy. Such a detection circuit 100 outputs a short-time width current pulse signal as a sensor signal, for example, a device such as Positron Emission Tomography (PET), Time-of-Fright PET, and photon counting CT used for cancer diagnosis. It has high utility value when it is incorporated as a signal processing circuit. It is not limited to a sensor that outputs a short-time width current pulse signal, but can also be used as a signal processing circuit for a sensor that outputs a signal that has a correlation between the peak value and the time width, such as monotonically increasing and then monotonically decreasing. It is possible.

The detection circuit 100 according to the present embodiment described above includes a one-shot circuit 150. One-shot circuit 150, as described above, to generate an extended signal S _p2 obtained by extending the signal end of the second comparison signal S _c2. If the one-shot circuit 150 is not provided and t ₂ is _{later than t 1} as shown in FIG. 10, the period from t _{1 to t 2} in the detection signal S _out is the Low level. Will be. To prevent such discontinuities, it generates a long signal S _p2 delayed until t ₃ is a time later than t ₂ by a one-shot circuit 150, and is inputted to the logic operation circuit 160.

_{However, if t 2} can always be set to a time earlier than t ₁ by adjusting the waveform shaping circuit 120 or the current comparator 140, the one-shot circuit 150 can be omitted. In this case, the signals input to the gate of the logical operation circuit 160 are _{two signals, the first comparison signal Sc1} and the second comparison signal _Sc2 .

As described above, the logic operation circuit 160 of the detection circuit 100 is an OR logic gate of three _{signals, the first comparison signal Sc1} , the second comparison signal _Sc2 , and the extension signal _Sp2. In addition to the extension signal S _p2 , the second comparison signal S _{c2 is also input when the rise of the extension signal S p2} is delayed with respect to the rise of the second comparison signal S _c2 depending on the configuration of the one-shot circuit 150. Because there is. However, if the delay is evaluated to be negligible, the logic operation circuit 160 may be an OR logic gate for inputting two signals _{, the first comparison signal Sc1} and the extension signal _Sp2.

Further, although the OR logic gate is used in the logic operation circuit 160 described above _{, the period with signals in each of the first comparison signal S c1} , the second comparison signal S _c2 , and the extension signal _{Sp 2} is set to the High level. The logic gate to be used may be selected depending on whether the level is Low or Low. Of course, some logic gates may be combined to generate a _{detection signal S out.}

Here, the detection result in the conventional ToT detection circuit and the detection result in one embodiment of the detection circuit 100 according to the present embodiment are compared. FIG. 12 is an example of the detection result in the conventional ToT detection circuit. Here, the horizontal axis is represented by energy (keV) as a signal amount proportional to the peak value, and the vertical axis is represented by time width (ns) as in FIG. In the figure, the 59.6 keV plot is ^{the measurement result of 241} Am, the 81 keV, 304 keV, 356 keV plot is the ¹³³ Ba measurement result, and the 122 keV plot is the ⁵⁷ Co measurement result, 604. The plots of ^{7 keV and 795.9 keV are the measurement results of 134} Cs, and the plots of 551 keV and 1275 keV are the measurement results of ^{22 Na.} As shown in the figure, the obtained measurement results draw an upwardly convex curve, and the linearity of energy (∝ peak value) and time width is not good.

FIG. 13 is an example of the detection result in one embodiment of the detection circuit 100 according to the present embodiment. Similar to FIG. 12, the horizontal axis is represented by energy (keV) and the vertical axis is represented by time width (ns). In the figure, the plot of 22 keV is ^{the measurement result of 100} Cd, the plot of 59.6 ^{keV is the measurement result of 241} Am, and the plot of 30.9 keV, 81 keV, 356 keV is the measurement result of ^{133 Ba.} The 122 keV plot is the ⁵⁷ Co measurement result, the 662 keV plot is the ¹³⁷ Cs measurement result, and the 551 keV plot is the ²² Na measurement result. As shown in the figure, the obtained measurement results are almost straight lines, and good linearity of energy (∝ peak value) and time width is obtained.

100 ... Detection circuit, 110 ... Current mirror circuit, 120 ... Waveform shaping circuit, 121 ... Slew rate limiting resistor circuit, 122 ... Change part, 130 ... Voltage comparator, 140 ... Current comparator, 150 ... One-shot circuit, 151 ... Time adjustment Part, 160 ... Logical operation circuit

Claims (5)

1. A current mirror circuit that copies the input sensor signal and outputs the first input signal and the second input signal in parallel,
   A waveform shaping circuit that adjusts the voltage fluctuation with respect to the elapsed time according to the set reference fluctuation when the first input signal is input and outputs the adjusted signal, and
   A voltage comparator that compares the voltage value of the adjustment signal with the reference voltage value and outputs the first comparison signal.
   A current comparator that compares the current value of the second input signal with the reference current value and outputs the second comparison signal.
   A logic operation circuit that performs a logical operation on the first comparison signal and the second comparison signal and outputs a detection signal that continues from the start time of the second comparison signal to the end time of the first comparison signal. Includes detection circuit.
2. It is provided with a one-shot circuit that generates and outputs an extension signal that extends the signal duration of the input second comparison signal.
   The detection circuit according to claim 1, wherein the logic operation circuit performs a logic operation on at least the first comparison signal and the extension signal and outputs the detection signal.
3. The detection circuit according to claim 2, wherein the one-shot circuit has a time adjusting unit for adjusting an extension time of the signal duration.
4. The detection circuit according to any one of claims 1 to 3, wherein the waveform shaping circuit has a change unit for changing the reference variation.
5. Claims 1 to 4 of the current mirror circuit are set so that the current ratio of the first input signal to the sensor signal is smaller than 1 and smaller than the current ratio of the second input signal to the sensor signal. The detection circuit according to any one of the above items.

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