WO2012121337A1

WO2012121337A1 - Distance measurement signal processing circuit and distance measuring apparatus

Info

Publication number: WO2012121337A1
Application number: PCT/JP2012/055986
Authority: WO
Inventors: 川人　祥二; 広記小川; 鈴木　高志
Original assignee: 国立大学法人静岡大学; 浜松ホトニクス株式会社
Priority date: 2011-03-08
Filing date: 2012-03-08
Publication date: 2012-09-13
Also published as: JP2014102072A

Abstract

A signal processing circuit (20) comprises a multistage amplifying circuit (30), N comparing circuits (40), N time measuring circuits (50) and a TOF estimating circuit (70). The second to N-th stage amplifying circuits (A(2) to A(N)) in the multistage amplifying circuit (30) are non-inverting amplifying circuits. The TOF estimating circuit (70) calculates delay time differences {T_m(n) - T_m(n + 1)} from measured times T_m(n) and T_m(n + 1) measured by the time measuring circuits (50), then estimates the magnitudes of measured signal current (Ip) on the basis of the delay time differences, thereafter estimates, on the basis of the magnitudes of the measured signal currents (Ip), delay times T_d(n) included in the measured times T_m(n), and subtracts the delay times T_d(n) from the measured times T_m(n), thereby calculating a flight time T_TOF. In this way, a wide distance range can be measured and the TOF can be measured with high precision.

Description

Distance measuring signal processing circuit and distance measuring device

The present invention relates to a signal processing circuit and a distance measuring device for distance measurement.

Patent Document 1 discloses a flight time (Time
Of Flight (TOF) measuring type distance measuring device is disclosed. The distance measuring device includes a transmitting unit that emits pulsed light and a receiving unit that receives the pulsed light reflected and returned from the object to be measured, and performs measurement based on the time from the transmission time point to the reception time point. Measure the distance to the distance object.

JP 2001-108747 A

The distance measurement by the TOF method is performed by irradiating a distance measurement object with a light pulse, detecting the reflected light, and obtaining the TOF of the light to the distance measurement object. Specifically, the light detection element receives the reflected light and outputs a current having a magnitude corresponding to the amount of light (hereinafter referred to as a measurement signal current). The measurement signal current is converted into a voltage signal by an amplifier and then input to an analog / digital conversion circuit. When the magnitude of the voltage signal output from the amplifier reaches a certain threshold value, the analog / digital conversion circuit represents the time waveform of the voltage signal by converting the voltage signal into a digital value in a short time interval. Create data. Then, the time centroid of the voltage signal is calculated from this data, and the TOF is calculated based on the time difference between the time centroid and the light pulse irradiation timing.

However, the TOF measured by the above method includes the time from when the reflected light is incident on the light detection element until the digital value is generated, that is, the delay time due to the signal delay in the circuit. That is, the measured TOF (hereinafter referred to as measurement time) T _m is represented by the following mathematical formula (1). Note that T _TOF is the original TOF, and T _d is the delay time in the circuit.

FIG. 11 is a graph showing an example of the relationship between the delay time _Td and the logarithmic value of the measurement signal current. As shown in FIG. 11, the delay time _Td tends to be shorter as the measurement signal current is larger. Therefore, when a wide range from a short distance to a long distance is a measurement target, a variation in reflected light intensity, that is, a variation in measurement signal current increases, and the delay time _Td greatly varies depending on the measurement distance. For this reason, highly accurate TOF measurement becomes difficult.

The present invention has been made in view of such problems, and provides a signal processing circuit and a distance measuring device for distance measurement that can measure a wide distance range and can measure TOF with high accuracy. For the purpose.

In order to solve the above-described problem, the first signal processing circuit for distance measurement according to the present invention performs the flight until the pulsed light emitted toward the distance measurement object is reflected by the distance measurement object and returned. A signal processing circuit used for time-based distance measurement, comprising: (1) first-stage to N-th stage amplifier circuits (N is an integer of 2 or more) connected in series with each other; A multi-stage amplifier circuit receiving a measurement signal current having a magnitude corresponding to the light intensity of the pulsed light reflected at the input terminal of the first stage amplifier circuit; and (2) connected to the first stage to the Nth stage amplifier circuit, respectively. N comparison circuits that output a significant value when the measurement signal voltage output from the corresponding amplifier circuit reaches the reference voltage, (3) a signal indicating the emission timing of the pulsed light, and N comparisons Inputs the signal output from the circuit and emits pulsed light A time measurement circuit for measuring each time (hereinafter referred to as the first to Nth measurement times) until the output signal of each comparison circuit becomes a significant value, and (4) signal delay in the signal processing circuit. First data representing a relationship between a delay time included in each measurement time and a measurement signal current, and a delay time difference which is a difference between a delay time included in one measurement time and a delay time included in another measurement time And a storage unit that preliminarily stores second data representing the relationship between the measurement signal current and (5) a calculation unit that calculates the flight time based on the first to Nth measurement times. The second to Nth stage amplifier circuits of the multistage amplifier circuit are constituted by non-inverting amplifier circuits. The calculation unit calculates a delay time difference from at least two measurement times among the first to Nth measurement times measured by the time measurement circuit, and determines the magnitude of the measurement signal current based on the delay time difference and the second data. Then, a delay time included in at least one of the first to Nth measurement times is obtained based on the magnitude of the measurement signal current and the first data, and at least one measurement time is obtained. The flight time is calculated by subtracting the delay time from.

In addition, the second signal processing circuit for distance measurement according to the present invention is used for distance measurement based on the flight time until the pulsed light emitted toward the distance measurement object is reflected by the distance measurement object and returned. (1) a first-stage to N-th stage amplifier circuit (N is an integer of 2 or more) connected in series with each other, and light of pulsed light reflected from a distance measuring object A multi-stage amplifier circuit that receives a measurement signal current having a magnitude corresponding to the intensity at the input terminal of the first-stage amplifier circuit; and (2) connected to the first-stage to N-th stage amplifier circuits, respectively. N comparison circuits that output a significant value when the output measurement signal voltage reaches the reference voltage, (3) a signal indicating the emission timing of the pulsed light, and a signal output from the N comparison circuits After the pulse light is emitted, the output of each comparison circuit A time measurement circuit for measuring each time until the signal becomes a significant value (hereinafter referred to as the first to Nth measurement times); and (4) a delay time included in each measurement time due to a signal delay in the signal processing circuit. And a storage unit that preliminarily stores first data representing the relationship between the measurement signal current and (5) a calculation unit that calculates a flight time based on the first to Nth measurement times. The second to Nth stage amplifier circuits of the multistage amplifier circuit are constituted by non-inverting amplifier circuits. The arithmetic unit calculates a difference between a delay time included in one measurement time and a delay time included in another measurement time from at least two measurement times among the first to Nth measurement times measured by the time measurement circuit. And calculating the magnitude of the measurement signal current based on the relationship between the delay time difference obtained from the first data and the measurement signal current, and the magnitude of the measurement signal current and the first data Based on the above, a delay time included in at least one of the first to Nth measurement times is obtained, and the flight time is calculated by subtracting the delay time from at least one measurement time.

In these signal processing circuits, when the measurement signal current based on the reflected light is input to the multistage amplifier circuit, the measurement signal current is converted into the measurement signal voltage by the first stage amplifier circuit, and this measurement signal voltage is converted to the second stage amplifier circuit. Or they are sequentially amplified by the Nth stage amplifier circuit. Then, the measurement signal voltage output from the amplifier circuit at each stage is input to the comparison circuit connected to each amplifier circuit. The comparison circuit outputs a significant value when the measurement signal voltage exceeds the reference voltage. At this time, since the amplifier circuit outputs a larger measurement signal voltage as it is located at a later stage, the later comparison circuit outputs a significant value earlier. Therefore, a difference occurs in the timing for outputting a significant value among the N comparison circuits. This difference appears as a difference between the first to Nth measurement times output from the time measurement circuit.

As will be described later, this difference in measurement time is equal to the difference (delay time difference) between the delay time included in one measurement time and the delay time included in another measurement time. Therefore, as in the first signal processing circuit described above, it is possible to obtain the magnitude of the measurement signal current by preparing in advance the second data representing the relationship between the delay time difference and the measurement signal current. Become. Furthermore, the delay time can be obtained by preparing in advance the first data representing the relationship between the delay time and the measurement signal current. Then, the original accurate TOF can be obtained by calculating the difference between the delay time and the measurement time.

Alternatively, as in the second signal processing circuit described above, by preparing first data representing the relationship between the delay time and the measurement signal current in advance, the delay time difference and the measurement signal current can be calculated from the first data. And the magnitude of the measurement signal current can be obtained from this relationship. Furthermore, it becomes possible to obtain the delay time from the magnitude of the measurement signal current using this first data. Then, the original accurate TOF can be obtained by calculating the difference between the delay time and the measurement time.

Further, in these signal processing circuits, the multistage amplifier circuit includes first to Nth stage amplifier circuits. According to the configuration in which a plurality of amplifier circuits are connected in this manner, even if the input measurement signal current is weak, a greatly amplified measurement signal voltage is output from the subsequent amplifier circuit. Therefore, the measurement time is suitably measured both when the measurement signal current is weak (that is, when the measurement distance is long) and when the measurement signal current is large (that is, when the measurement distance is short), and an accurate TOF is obtained. Can be calculated.

Thus, according to the first and second signal processing circuits for distance measurement described above, a wide distance range can be measured, and TOF can be measured with high accuracy.

Further, in these signal processing circuits, the arithmetic unit obtains a delay time included in two or more measurement times from the first to Nth measurement times based on the measurement signal current and the first data. After calculating two or more flight times by subtracting the delay time from the above measurement time, an average value of the two or more flight times may be calculated. With such a configuration, a more accurate TOF can be calculated.

The distance measuring device according to the present invention measures the distance to the distance measuring object based on the flight time until the pulsed light emitted toward the distance measuring object is reflected by the distance measuring object and returned. A distance measuring device comprising: (1) one of the signal processing circuits described above; (2) a light emitting unit that emits pulsed light toward a distance measuring object; and (3) reflected from the distance measuring object. A light detection unit that receives the pulsed light and generates a measurement signal current having a magnitude corresponding to the light intensity of the pulsed light. According to this distance measuring device, by providing any of the signal processing circuits described above, a wide distance range can be measured, and TOF can be measured with high accuracy.

According to the signal processing circuit and the distance measuring device for distance measurement according to the present invention, a wide distance range can be measured and the TOF can be measured with high accuracy.

It is the schematic which shows the structure of the distance measuring device which concerns on one Embodiment. It is a figure which shows an example of an internal structure of a signal processing circuit. It is a circuit diagram which shows the specific structural example of a multistage amplifier circuit. It is a circuit diagram which shows the specific structural example of a time measurement circuit. 4 is a timing chart for explaining the concept of measurement time measured by the time measurement circuit, which is output from the time waveform of the pulsed light, the time waveform of the reflected pulsed light, and the first to third stage amplifier circuits. A time waveform of the measurement signal voltage is shown. It is a flowchart which shows the TOF calculation method in a TOF estimation circuit. It is a graph which shows an example of the relationship between a measurement signal current and delay time in the 6-stage amplifier circuit comprised by 6 amplifier circuits which have the mutually same characteristic. It is a graph which shows an example of the relationship between delay time difference and measurement signal current. It is a figure which shows roughly the method of estimating the magnitude | size of a measurement signal current from a delay time difference. It is a figure which shows roughly the method of estimating delay time from a measurement signal current. It is a graph which shows an example of the relationship between delay time and a measurement signal current.

Hereinafter, embodiments of a signal processing circuit and a distance measuring device for distance measurement according to the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

FIG. 1 is a schematic diagram showing a configuration of a distance measuring apparatus according to the present embodiment. This distance measuring device 10 emits pulsed light P1 toward the distance measuring object B, and when the light (reflected pulsed light) P2 reflected by the distance measuring object B of the pulsed light P1 returns, the reflected pulsed light P2 , And the distance to the distance measuring object B is measured based on the time (TOF) from the emission of the pulsed light P1 to the detection of the reflected pulsed light P2. As shown in FIG. 1, the distance measuring device 10 receives a light emitting unit 11 that emits pulsed light P <b> 1 toward the distance measuring object B, and reflected pulsed light P <b> 2 reflected by the distance measuring object B. And a light detection unit 12. The light emitting unit 11 includes, for example, a laser diode. The light detection unit 12 includes, for example, a photodiode, and generates a measurement signal current Ip having a magnitude corresponding to the light intensity of the reflected pulsed light P2.

The distance measuring device 10 further includes a signal processing circuit 20 that receives the measurement signal current Ip output from the light detection unit 12 and calculates TOF. The signal processing circuit 20 amplifies the voltage signal after converting the measurement signal current Ip into a voltage signal. Then, the TOF is calculated based on the difference between the timing at which the amplified voltage signal exceeds the reference voltage and the timing at which the pulsed light P1 is emitted from the light emitting unit 11.

FIG. 2 is a diagram illustrating an example of the internal configuration of the signal processing circuit 20. As shown in FIG. 2, the signal processing circuit 20 includes a multistage amplifier circuit 30, N (N is an integer of 2 or more) comparison circuits (comparators) 40, N time measurement circuits 50, and a storage unit 60 and a TOF estimation circuit 70.

The multistage amplifier circuit 30 includes first to Nth stage amplifier circuits A (1) to A (N). These amplifier circuits A (1) to A (N) are connected in series with each other. In other words, the signal output terminal of the amplifier circuit A (n) and the signal input terminal of the amplifier circuit A (n + 1) are electrically connected to each other. However, n is an integer of 1 or more and (N-1) or less. The measurement signal current Ip is input from the light detection unit 12 to the signal input terminal of the first stage amplifier circuit A (1).

The signal input terminals of the N comparison circuits 40 are electrically connected to the signal output terminals of the first to Nth stage amplifier circuits A (1) to A (N), respectively. Also, a common reference voltage Vref is input to these comparison circuits 40. These comparison circuits 40 are provided with voltages output from the corresponding amplifier circuits A (1), A (2),..., Or A (N) (hereinafter referred to as measurement signal voltages) V _O (1), V _O (2), ···, or _{if V} O (N) has reached the reference voltage Vref, the output signal _{_{S C (1), S C}} (2), ···, or as _S C (N) Output a value of significant logic level.

Signals S _C (1) to S _C (N) output from the N comparison circuits 40 are input to the N time measurement circuits 50, respectively. The N time measuring circuits 50 receive a signal Sstart indicating the emission timing of the pulsed light P1. This signal Sstart is provided from the light emitting unit 11 to each time measurement circuit 50, for example. Each of the N time measurement circuits 50 outputs the output signal S _C (1) of each comparison circuit 40 after the pulsed light P1 is emitted based on the signals S _C (1) to S _C (N) and the signal Sstart. ) To S _C (N) are measured each time until it becomes a significant value. In the following description, the time from when the pulsed light P1 is emitted until the output signal S _C (k) becomes a significant value is referred to as “kth measurement time T _m (k)”. However, k is an integer from 1 to N.

Here, FIG. 3 is a circuit diagram showing a specific configuration example of the multistage amplifier circuit 30. In the multistage amplifier circuit 30 shown in FIG. 1, the first stage amplifier circuit A (1) is configured by an integration circuit including an amplifier 31 and an integration capacitor 32. The integrating capacitive element 32 is connected between the inverting input terminal and the output terminal of the amplifier 31, and the measurement signal current Ip is input to the inverting input terminal of the amplifier 31. Therefore, the measurement signal current Ip is stored in the integration capacitor element 32. The potential of the non-inverting input terminal of the amplifier 31 is set to the reference potential V _CM. With such a configuration, a voltage corresponding to the integral value of the measurement signal current Ip, that is, the measurement signal voltage V _O (1) is generated at the output terminal of the amplifier 31. Note that a reset switch 33 is connected in parallel with the integration capacitor element 32 in order to reset the electric charge stored in the integration capacitor element 32.

The second to Nth stage amplifier circuits A (2) to A (N) are constituted by non-inverting amplifier circuits including an amplifier 34, a feedback capacitive element 35, and a load capacitive element 36. The feedback capacitive element 35 is connected between the inverting input terminal and the output terminal of the amplifier 34, and the load capacitive element 36 is connected between the inverting input terminal of the amplifier 34 and the ground potential line. Then, the measurement signal voltages V _O (1), V _O (2),..., V _O from the amplifier circuits A (1), A (2) _,. (N−1) is input to the non-inverting input terminal of the amplifier 34. With this configuration, at the output terminals of the amplifiers 34 of these amplifier circuits A (2) to A (N), the measurement signal voltage V _O (from the previous amplifier circuits A (1) to A (N−1) is obtained. In-phase measurement signal voltages V _O (2) to V _O (N) in which 1) to V _O (N-1) are amplified are generated. Note that a reset switch 37 is connected in parallel with the feedback capacitive element 35 in order to reset the charge stored in the feedback capacitive element 35.

FIG. 4 is a circuit diagram illustrating a specific configuration example of the time measurement circuit 50. The time measuring circuit 50 shown in the figure includes a so-called TDC (Time to Digital Converter) circuit, and includes a plurality of D-type flip-flops 51, a plurality of delay circuits 52 connected in series, an encoder 53, and the like. , A reference clock circuit 54, a counter circuit 55, and a processing circuit 56. The reference clock circuit 54 starts operation in response to the input of a signal Sstart indicating the emission timing of the pulsed light P1. The reference clock CLK output from the reference clock circuit 54 is input to the first delay circuit 52. Each delay circuit 52 outputs a reference clock that is sequentially delayed. These reference clocks are input to the D terminal of each D-type flip-flop 51. In addition, a signal that rises in response to a change of the signal S _C (k) from the comparison circuit 40 to a significant logic level is input to the CK terminal of each D-type flip-flop 51. The Q output of each D-type flip-flop 51 is provided to the encoder 53. As a result, the encoder 53 identifies which delay circuit 52 is outputting the reference clock at the time when the signal S _C (k) changes to a significant logic level. On the other hand, the counter circuit 55 counts the reference clock CLK output from the reference clock circuit 54. The count signal output from the counter circuit 55 is input to the processing circuit 56. Based on the information provided from the encoder 53 and the count signal from the counter circuit 55, the processing circuit 56 outputs a significant value of the output signal S _C (k) of the comparison circuit 40 after the pulsed light P1 is emitted. Digital data corresponding to the k-th measurement time T _m (k) up to is generated.

FIG. 5 is a timing chart for explaining the concept of the measurement time measured by the time measurement circuit 50. FIG. 5 shows the time waveform (graph G1) of the pulsed light P1, the time waveform (graph G2) of the reflected pulsed light P2, and the first to third stage amplifier circuits A (1) to A (3). The time waveforms (graphs G3 to G5) of the output measurement signal voltages V _O (1) to V _O (3) are shown. In Figure 5, the pulse light P1 is emitted in a certain time t _1, the reflected pulse light P2 is detected at time t _2. The time T _TOF from time t ₁ to time t ₂ is the true time of flight (TOF). Further, the measurement signal voltages V _O (1) to V _O (3) rise gently with a certain time constant. This is mainly due to a delay that occurs when a signal passes through the circuit from the light detection unit 12 (see FIG. 2) to the comparison circuit 40. Since the measurement signal voltages V _O (1) to V _O (3) have larger absolute values as the latter stage, the time (delay time) until reaching a certain reference voltage Vref is the latter stage if the time constant is the same. The faster you get. In the figure, delay times T _d (1) to T _d (3) until each of the measurement signal voltages V _O (1) to V _O (3) reaches the reference voltage Vref are shown, and T _d (1 )> T _d (2)> T _d (3).

The measurement time measured by the time measurement circuit 50 is the sum of the true flight time T _TOF and the delay times T _d (1) to T _d (3) shown in FIG. That is, the measurement time T _m (1) measured for the measurement signal voltage V _O (1) = T _TOF + T _d (1), and the measurement time T _m (2) measured for the measurement signal voltage V _O (2). ) = T _TOF + T _d (2) and the measurement time T _m (3) measured for the measurement signal voltage V _O (3) = T _TOF + T _d (3).

Reference is again made to FIG. The TOF estimation circuit 70 is a calculation unit in the present embodiment, and is based on the first to Nth measurement times T _m (1) to T _m (N) provided from the N time measurement circuits 50. Is calculated. FIG. 6 is a flowchart showing a TOF calculation method in the TOF estimation circuit 70. Hereinafter, the TOF calculation method will be described in detail with reference to FIG.

Now, the measurement time T _m (n) measured based on the measurement signal voltage V _O (n) output from the n-th stage amplifier circuit A (n) is expressed by the following equation (2).

The measurement time T _m (n + 1) related to the measurement signal voltage V _O (n + 1) output from the (n + 1) -th stage amplifier circuit A (n + 1) is expressed by the following equation (3).

In the formulas (2) and (3), the distance to the distance measurement object B is constant, so that the true flight time T _TOF is equal to each other. Therefore, when the difference between the formula (2) and the formula (3) is obtained, the term relating to the true flight time T _TOF can be eliminated as in the following formula (4).

As shown in Equation (4), the difference between the measurement time T _m (n + 1) and the measurement time T _m (n) is equal to the difference between the delay time T _d (n + 1) and the delay time T _d (n). .

Here, FIG. 7 shows the logarithmic value of the measurement signal current Ip and the delay time T _d (1) in a six-stage amplifier circuit constituted by six amplifier circuits A (1) to A (6) having the same characteristics. ) To T _d (6) is a graph showing an example of the relationship. In the drawing, graphs G11 to G16 respectively show delay times T _d (1) to T _d (6). Further, in the figure, a feedback capacitor _{C 1} of the amplification circuit A (1) of the first stage and 0.1 [pF], the pulse width of the measurement signal current Ip and 10 [nsec], of the measured signal current Ip While changing the current value, the delay times T _d (1) to T _d (6) were measured.

As shown in FIG. 7, the delay times T _d (1) to T _d (6) tend to become shorter as the current value of the measurement signal current Ip increases. Further, if the relationship between the measurement signal current Ip and the delay time T _d (n) as shown in the figure is acquired in advance, the delay time T _d (n) can be estimated from the measurement signal current Ip. .

FIG. 8 is a graph showing an example of the relationship between the difference between the delay times T _d (1) to T _d (6) and the logarithmic value of the measurement signal current Ip. The difference between the delay times T _d (1) to T _d (6) is, for example, the difference between the delay times T _d (1) and T _d (2) (graph G21), and the delay time T _d The difference between (2) and T _d (3) (graph G22), the difference between the delay times T _d (3) and T _d (4) (graph G23), and the delay time T _d (4) T is _d (5) the difference between (graph G24), which is the difference between the delay time _T d (5) and _T d (6) (graph G25). Also in FIG. 8, as in FIG. 7, the delay time difference tends to become shorter as the measurement signal current Ip increases.

As is clear from FIG. 8, if the relationship between the delay time difference and the measurement signal current Ip is acquired in advance, the magnitude of the measurement signal current Ip can be estimated from the delay time difference. As described above, the difference between the measurement time T _m (n + 1) and the measurement time T _m (n) is equal to the difference between the delay time T _d (n + 1) and the delay time T _d (n). Further, the difference between the measurement time T _m (n + 1) and the measurement time T _m (n) is easily calculated from the measurement result in the time measurement circuit 50.

Therefore, in the present embodiment, first data representing the relationship between the delay time T _d (n) and the measurement signal current Ip as shown in FIG. 7, and the relationship between the delay time difference and the measurement signal current Ip as shown in FIG. Is stored in advance in the storage unit 60. Then, the TOF estimation circuit 70 delays from at least two measurement times T _m (n) and T _m (n + 1) among the measurement times T _m (1) to T _m (N) provided from the time measurement circuit 50. The time difference {T _d (n + 1) −T _d (n)} is calculated (step S11 in FIG. 6). Thereafter, the TOF estimation circuit 70 uses the second data stored in the storage unit 60 to calculate the measurement signal current from the delay time difference {T _d (n + 1) −T _d (n)} as shown in FIG. The magnitude of Ip is estimated (step S12 in FIG. 6). As shown in FIG. 10, the TOF estimation circuit 70 uses the first data stored in the storage unit 60 to calculate the delay time T _d (n) or T _d (n + 1) from the estimated measurement signal current Ip. Is estimated (step S13). Finally, the TOF estimation circuit 70 uses the estimated delay time T _d (n) or T _d (n + 1) as the measurement time T _m (n) or T _m (n + 1) as shown in the following equation (5). By subtracting from, an accurate flight time T _TOF is calculated (step S14).

In the above example, the flight time T is based on the measurement signal voltages V _O (n + 1) and V _O (n) from the (n + 1) -th and n-th amplifier circuits A (n + 1) and A (n). _{The TOF} is calculated, but the combination of the measurement signal voltages is not limited to this, and is based on the measurement signal voltages output from any two of the N amplifier circuits A (1) to A (N). Thus, the flight time T _TOF can be obtained by the same procedure.

Ideally, the calculated time of flight T _TOF should be equal regardless of the combination of the measurement signal voltages. However, in practice, a quantization error or the like at the time of digital conversion influences, and the flight time T _TOF varies depending on the combination of measurement signal voltages. Therefore, the TOF estimation circuit 70, based on the measurement signal current Ip and the first data, measures two or more measurement times T _m (p), T _m among the measurement times T _m (1) to T _m (N). (Q) (where p and q are integers of 1 or more and N or less, and delay times T _d (p) and T _d (q) included in p ≠ q) are obtained, and two or more measurement times T _m ( After calculating two or more flight times T _TOF by subtracting the delay times T _d (p) and T _d (q) from p) and T _m (q), an average value of these may be calculated. More preferably, as shown in the following formula (6), the average of the differences between all the measurement times T _m (1) to T _m (N) and the delay times T _d (1) to T _d (N) The value may be obtained as the time of flight _TTOF . As a result, a more accurate flight time T _TOF can be obtained.

As described above, according to the signal processing circuit 20 of the present embodiment, the delay time caused by the signal delay of the circuit portion can be suitably removed from the measurement time, so that the flight time T _TOF can be obtained with high accuracy. Can be measured. In the signal processing circuit 20, the multistage amplifier circuit 30 includes first to Nth stage amplifier circuits A (1) to A (N). With the configuration in which a plurality of amplifier circuits are connected in this way, even if the input measurement signal current Ip is weak, a greatly amplified measurement signal voltage is output from the subsequent amplifier circuit. Therefore, the measurement time is suitably measured both when the measurement signal current Ip is weak (that is, when the measurement distance is long) and when the measurement signal current Ip is large (that is, when the measurement distance is short). The flight time T _TOF can be calculated.

The effect of expanding the dynamic range by the multistage amplifier circuit 30 will be described in more detail. The measurement signal current Ip input to the multistage amplifier circuit 30 is inverted and amplified by a first stage amplifier circuit A (1) configured as an integration circuit. At this time, the measurement signal voltage V _O (1) output from the first stage amplifier circuit A (1) is expressed as the following Expression (7). In Equation (7), C _f1 is the feedback capacitance value of the first stage amplifier circuit A (1).

Further, the measurement signal voltage V _O (1) from the first stage amplifier circuit A (1) is directly input to the second stage amplifier circuit A (2) configured as a non-inverting amplifier circuit. The measurement signal voltage V _O (2) from the second-stage amplifier circuit A (2) is expressed as the following equation (8). In Equation (8), C _f2 is the feedback capacitance value of the second stage amplifier circuit A (2), and C _i2 is the load capacitance value of the second stage amplifier circuit A (2).

As is clear from Equation (8), the amplification factor in the second stage amplifier circuit A (2) is determined by the feedback capacitance value C _f2 and the load capacitance value C _i2 .

The measurement signal voltages V _O (3) to V _O (N) output from the amplifier circuits A (3) to A (N) after the third stage do not invert the voltage output from the amplifier circuit of the previous stage. Since it is amplified, it is in phase with the measurement signal voltage V _O (1). The measurement signal voltage V _O (N) output from the Nth stage amplifier circuit A (N) is expressed as the following equation (9). In Equation (9), C _fN is the feedback capacitance of the Nth stage amplifier circuit A (N), C _iN is the load capacitance value of the Nth stage amplifier circuit A (N), and C _N is C _fN and C It is a composite capacity ratio calculated from _iN .

As is clear from Equation (9), the measurement signal voltage V _O (N) of the Nth stage amplifier circuit A (N) is the second to Nth stage amplifier circuits A (2) to A (N). Of the combined capacitance ratios C ₂ to C _N and the measurement signal voltage V _O (1) of the first stage amplifier circuit A (1).

In this way, by connecting a plurality of non-inverting amplifier circuits in multiple stages, the measurement signal voltage V _O (N) is greatly amplified in the subsequent amplification circuit A (N) even if the measurement signal current Ip is weak. be able to. Therefore, according to the multistage amplifier circuit 30 of this embodiment, when the reflected pulse light P2 is weak (that is, when the measurement distance is long) and when the reflected pulse light P2 is strong (that is, when the measurement distance is short). In any case, it is possible to suitably measure at least two of the measurement times T _m (1) to T _m (N) and calculate the flight time T _TOF .

Note that the graphs G11 to G16 shown in FIG. 7 described above are multi-stage so that the combined capacitance ratios C ₂ to C ₆ of the amplification circuits A (2) to A (6) after the second stage are 11. This is a result of measuring the delay times T _d (1) to T _d (6) by fabricating the amplifier circuit 30. Referring to FIG. 7, it is possible to detect a measurement signal current Ip in a range of 5 digits from 10 [nA] to 1 [mA] by a 6-stage amplifier circuit. When attention is paid to the delay time T _d (6) in the sixth-stage amplifier circuit A (6), in the region where the measurement signal current exceeds 100 [μA], the delay time T _d (6) of the measurement signal current Ip The change is getting smaller. This indicates that the sixth stage amplifier circuit A (6) is saturated. Even in such a case, by using the measurement signal voltages V _O (1) to V _O (5) from the other non-saturated amplifier circuits A (1) to A (5), A plurality of measurement times T _m (1) to T _m (5) can be obtained for one measurement signal current Ip, and the flight time is based on these measurement times T _m (1) to T _m (5). T _TOF can be determined.

The signal processing circuit and distance measuring apparatus for distance measurement according to the present invention are not limited to the above-described embodiments, and various other modifications are possible. For example, in the above embodiment, the first stage amplifier circuit of the multistage amplifier circuit has an inverting configuration, but the first stage amplifier circuit may be a non-inverting type.

In the above embodiment, the storage unit stores in advance second data representing the relationship between the delay time difference and the measurement signal current, and the calculation unit performs measurement based on the calculated delay time difference and the second data. The magnitude of the signal current is obtained. However, even in the case where only the first data representing the relationship between the delay time and the measurement signal current is stored in the storage unit, the calculation unit calculates the difference between the delay time and the measurement signal current from the first data. Since the relationship (see FIG. 9) can be obtained by calculation, the magnitude of the measurement signal current can be obtained from this relationship.

The present invention can be used as a signal processing circuit for distance measurement and a distance measuring device capable of measuring a wide distance range and measuring TOF with high accuracy.

DESCRIPTION OF SYMBOLS 10 ... Distance measuring device, 11 ... Light emission part, 12 ... Light detection part, 20 ... Signal processing circuit, 30 ... Multistage amplifier circuit, 31, 34 ... Amplifier, 32 ... Integration capacity element, 35 ... Feedback capacity element, 36 ... Load capacitance element, 40 ... comparison circuit, 50 ... time measurement circuit, 51 ... D-type flip-flop, 52 ... delay circuit, 53 ... encoder, 54 ... reference clock circuit, 55 ... counter circuit, 56 ... processing circuit, 60 ... memory 70: TOF estimation circuit, A (1) to A (N) ... amplification circuit, B ... object to be measured, CLK ... reference clock, Ip ... measurement signal current, P1 ... pulse light, P2 ... reflected pulse light, V _O (1) to V _O (N): measurement signal voltage, Vref: reference voltage.

Claims

A signal processing circuit used for distance measurement based on a flight time until the pulsed light emitted toward the distance measurement object is reflected by the distance measurement object and returned.
A measurement signal having first to Nth stage amplification circuits (N is an integer of 2 or more) connected in series, and having a magnitude corresponding to the light intensity of the pulsed light reflected from the distance measuring object. A multi-stage amplifier circuit receiving current at an input terminal of the first-stage amplifier circuit;
N comparison circuits connected to the first to Nth stage amplifier circuits, respectively, for outputting a significant value when the measurement signal voltage output from the corresponding amplifier circuit reaches a reference voltage;
A signal indicating the emission timing of the pulsed light and a signal output from the N comparison circuits are input, and each signal from when the pulsed light is emitted until the output signal of each comparison circuit reaches the significant value. A time measurement circuit for measuring time (hereinafter referred to as first to Nth measurement times);
First data representing a relationship between a delay time included in each measurement time and the measurement signal current due to a signal delay in the signal processing circuit, and the measurement time different from the delay time included in one measurement time A storage unit that preliminarily stores second data representing a relationship between a delay time difference that is a difference from the delay time included in the measurement signal current;
A calculation unit that calculates the flight time based on the first to Nth measurement times;
The second to Nth stage amplifier circuits of the multistage amplifier circuit are constituted by non-inverting amplifier circuits,
The computing unit calculates the delay time difference from at least two of the first to Nth measurement times measured by the time measurement circuit, and based on the delay time difference and the second data. The magnitude of the measurement signal current is obtained and then included in at least one of the first to Nth measurement times based on the magnitude of the measurement signal current and the first data. A signal processing circuit for distance measurement, wherein a delay time is obtained and the flight time is calculated by subtracting the delay time from the at least one measurement time.
A signal processing circuit used for distance measurement based on a flight time until the pulsed light emitted toward the distance measurement object is reflected by the distance measurement object and returned.
A measurement signal having first to Nth stage amplification circuits (N is an integer of 2 or more) connected in series, and having a magnitude corresponding to the light intensity of the pulsed light reflected from the distance measuring object. A multi-stage amplifier circuit receiving current at an input terminal of the first-stage amplifier circuit;
N comparison circuits connected to the first to Nth stage amplifier circuits, respectively, for outputting a significant value when the measurement signal voltage output from the corresponding amplifier circuit reaches a reference voltage;
A signal indicating the emission timing of the pulsed light and a signal output from the N comparison circuits are input, and each signal from when the pulsed light is emitted until the output signal of each comparison circuit reaches the significant value. A time measurement circuit for measuring time (hereinafter referred to as first to Nth measurement times);
A storage unit that stores in advance first data representing a relationship between a delay time included in each measurement time and the measurement signal current due to a signal delay in the signal processing circuit;
A calculation unit that calculates the flight time based on the first to Nth measurement times;
The second to Nth stage amplifier circuits of the multistage amplifier circuit are constituted by non-inverting amplifier circuits,
The computing unit may change the measurement time different from the delay time included in one measurement time from at least two of the first to N measurement times measured by the time measurement circuit. After calculating a delay time difference that is a difference from the included delay time, after obtaining the magnitude of the measurement signal current based on the relationship between the delay time difference obtained from the first data and the measurement signal current, Based on the magnitude of the measurement signal current and the first data, the delay time included in at least one of the first to Nth measurement times is obtained, and the delay time is calculated from the at least one measurement time. A signal processing circuit for distance measurement, wherein the flight time is calculated by reducing a delay time.
The calculation unit obtains the delay time included in two or more of the first to Nth measurement times based on the measurement signal current and the first data, and the two or more 3. The distance measurement device according to claim 1, wherein after calculating the two or more flight times by subtracting the delay time from the measurement time, an average value of the two or more flight times is calculated. Signal processing circuit.
A distance measuring device for measuring a distance to the distance measuring object based on a flight time until the pulsed light emitted toward the distance measuring object is reflected by the distance measuring object and returned.
A signal processing circuit according to any one of claims 1 to 3,
A light emitting unit that emits the pulsed light toward the object to be measured;
A distance measuring device comprising: a light detection unit that receives the pulsed light reflected from the distance measuring object and generates the measurement signal current having a magnitude corresponding to the light intensity of the pulsed light.