JPH10132927A - Timing circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a timing circuit with high-accuracy such that time resolution is independent of a clock rate of an oscillator. SOLUTION: A counting operation in a counter 8 is stopped by a receiving timing pulse which is output from a receiving timing detecting circuit 10. In addition, when the receiving timing pulse is output, received signals are sampled by a clock pulse which is generated by a received wave sampling circuit 11 and the sampled signals is converted to digital data by an A/D converter 12. The digital data are sent to a microcomputer 9 where a zero-cross-point Pc of the received signal is determined by interpolation process. An elapsed-time T0 between transmitting and receiving of ultrasonic is calculated, based on an elapsed-time (Δt+tc ) between the zero-cross point Pc of the received wave signal which is determined through the interpolation process and a receiving timing pulse position, end an elapsed-time Ta determined by a counter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a time measuring circuit using a clock pulse, and more particularly to a time measuring circuit suitable for measuring the propagation time of an ultrasonic wave.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram of a conventional time measuring circuit, and FIG. 5 is a time chart thereof. The waveforms (a) to (e) in FIG. 5 are the same as those in FIG.
(E) shows the waveform of the position.

In FIG. 4, 1 is an oscillator for generating a clock pulse serving as a time reference, 2 is a transmission timing generation circuit for generating a transmission timing pulse, 3 is a transmission circuit for a high frequency signal for ultrasonic waves, and 4 is a circuit for transmitting a high frequency signal. A transmitting ultrasonic transducer for converting into a sound wave, a receiving ultrasonic transducer for converting a received ultrasonic wave into an electric signal, a receiving circuit, a zero-cross detecting circuit for generating a receiving timing pulse of a receiving wave signal , 8 are counters for measuring time, and 9 is a microcomputer for calculating measurement time.

The operation of the above conventional circuit will be described with reference to a time chart of FIG. As shown in FIG. 5D, the oscillator 1 constantly oscillates a clock pulse of, for example, 1 MHz as a time reference. This clock pulse is transmitted to the transmission timing circuit 2 and the clock terminal CLK of the counter 8.
Sent to Based on the clock pulse, the transmission timing generation circuit 2 generates a transmission timing pulse at a predetermined time position synchronized with the clock pulse as shown in FIG. Send to The transmission circuit 3 sends a high-frequency signal for generating an ultrasonic wave to the transducer 4 for transmission in synchronization with the transmission timing pulse. This allows transjuusa 4
Transmits ultrasonic waves. On the other hand, when receiving the transmission timing pulse from the transmission timing generation circuit 2, the counter 8 starts counting the clock pulse of the oscillator 1 as shown in FIG.

When the ultrasonic wave transmitted from the transmitting transducer 4 is received by the receiving ultrasonic transducer 5, the received wave signal is transmitted to the zero cross circuit 7 via the receiving circuit 6. The zero cross circuit 7 is shown in FIG.
Detecting a zero-cross point P _C of the received wave signal shown in (a),
In this zero-cross point P _C position, generates a reception timing pulses as shown in FIG. 5 (c).

[0006] Originally, the receiving point of the ultrasonic wave is the point P ₀ which is the first rising position of the received wave signal. However, the signal level of the point P ₀ is small and unstable, and is buried in noise or the like. In addition, it is difficult to reliably detect.
Therefore, usually, the time measuring circuit of this kind, the received wave signal is to detect the stable next zero-cross point P _C located in level manner as the time measurement points. This P
_{When the} point _{C is} set as the time measurement point, the measurement time becomes longer by one cycle time ΔT of the transmission frequency of the ultrasonic wave as it is, but the transmission frequency of the ultrasonic wave is known in advance in the circuit design, so that it will be described later. to, by'll minus one cycle time ΔT of the oscillation frequency of the ultrasonic wave from the measurement time to the P _C point, and output as the final measurement time T _0.

The reception timing pulse output from the zero cross detection circuit 7 is sent to the counter 7 and
As shown in (e), the count of the clock pulse is stopped by the reception timing pulse. Thus the count number n of the resulting clock pulses in the counter 8 indicates the time interval from the transmission position of the ultrasound to the P _C position the zero cross point. Then, the microcomputer 9 uses the count number n obtained by the counter 8 and multiplies the count number by one clock width (the reciprocal of the frequency) of the clock pulse to obtain an elapsed time T _n = (Δt × n). calculating a further, after subtraction of one cycle time ΔT of the oscillation frequency of the ultrasonic wave from the elapsed time T _n, and outputs as the final measurement time T _0.

[0008]

[SUMMARY OF THE INVENTION However, the conventional time measuring circuit described above, as shown in FIG. 5 (e), between the last counted n th clock pulse position and the zero-cross point P _C A certain error δt occurs. This error δt is unavoidable on the measurement principle, and its maximum value is one clock width Δt of the clock pulse. Therefore, the time resolution in the conventional time measurement circuit is determined by the frequency of the clock pulse of the oscillator 1, and a resolution of at most one clock width Δt can be obtained. For this reason, in order to increase the time resolution in the conventional time measuring circuit, it is necessary to use an oscillator or a counting circuit having an extremely high oscillation frequency, which causes an increase in cost and an increase in power consumption. . Further, there is also a problem that circuit wiring is restricted due to problems such as clock noise, and circuit design cannot be freely performed.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a high-precision time measurement circuit whose time resolution is not limited by the clock frequency of an oscillator. .

[0010]

According to the present invention, there is provided a time measuring circuit for measuring an elapsed time from transmission to reception of an ultrasonic wave by counting clock pulses output from an oscillator. A reception timing detection circuit that generates a reception timing pulse when the signal level of the ultrasonic reception wave signal reaches a predetermined level, and starts counting clock pulses from a transmission start position of the ultrasonic wave, and the reception timing detection circuit A counter that stops counting when a reception timing pulse is output from a reception wave sampling circuit that starts sampling a reception wave signal using a clock pulse from the time when the reception timing pulse is output from the reception timing detection circuit, Sampling output from the reception wave sampling circuit A for converting No. into digital data
A zero-cross point of the received wave signal is obtained by interpolation processing based on the / D converter and the sampling data sent from the A / D converter. And calculating means for calculating an elapsed time from transmission to reception of the ultrasonic wave by using the elapsed time to the reception timing pulse position.

[0011]

In the case of the time measuring circuit according to the present invention, the counter starts counting clock pulses from the ultrasonic wave transmission start position and stops counting when the reception timing pulse is output from the reception timing detection circuit.
On the other hand, the reception wave sampling circuit starts sampling the reception wave signal using the clock pulse from the time when the reception timing pulse is output from the reception timing detection circuit, and sends the obtained sampling data to the arithmetic means.

The calculating means obtains a zero cross point of the received wave signal by interpolation processing based on the sampling data obtained by the received wave sampling circuit, and calculates a time interval between the zero cross point and the reception timing pulse by a proportional calculation. I do. Then, an elapsed time from transmission to reception of the ultrasonic wave is calculated from the obtained time interval and the elapsed time to the reception timing pulse position obtained by the counter.

As described above, in the case of the present invention, the zero-cross point of the received wave signal is obtained by the interpolation process. Therefore, the higher the accuracy of the interpolation process, the higher the accuracy of the calculation position of the zero-cross point. For this reason, the time resolution does not depend on the frequency of the clock pulse of the oscillator, the time resolution can be increased to the pulse width of the clock pulse or less, and a more accurate measurement time can be obtained.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an embodiment of a time measuring circuit according to the present invention, FIG. 2 is a time chart thereof, and FIG. 3 is an explanatory diagram of an interpolation process. The waveforms (a) to (c) in FIG. 2 are the same as those in FIG.
(C) shows the waveform of the position.

In FIG. 1, 1 is an oscillator, 2 is a transmission timing generation circuit, 3 is a transmission circuit, 4 is an ultrasonic transducer for transmission, 5 is an ultrasonic transducer for reception, 6 is a reception circuit, 6 is a reception circuit, 8 is a counter, Reference numeral 9 denotes a microcomputer, and these circuits are the same as the above-described conventional time measuring circuit. The present invention uses a reception timing detection circuit 1 instead of the zero cross detection circuit 7 of the conventional circuit.
0 and the received wave sampling circuit 11 and A
A / D converter 12 is additionally provided. The reception timing detection circuit 10 generates a reception timing pulse when the signal level of the ultrasonic reception wave signal reaches a predetermined level. The reception wave sampling circuit 11 outputs the reception timing pulse from the reception timing detection circuit. A circuit that samples a received wave signal using a clock pulse from a point in time, and an A / D converter 12 is a conversion circuit that converts sampling data into digital data and sends the digital data to the microcomputer 9.

Next, the operation of the above circuit will be described with reference to the time chart of FIG. As shown in FIG. 2D, the oscillator 1 constantly oscillates a clock pulse of, for example, 1 MHz as a time reference. This clock pulse is sent to the transmission timing generation circuit 2, the counter 8, and the reception wave sampling circuit 11 clock terminal CLK. Based on the clock pulse, the transmission timing generation circuit 2 generates a transmission timing pulse at a predetermined time position synchronized with the clock pulse, as shown in FIG. Send to The transmission circuit 3 sends a high-frequency signal for generating an ultrasonic wave to the transducer 4 for transmission in synchronization with the transmission timing pulse. As a result, ultrasonic waves are transmitted from the transducer 4. On the other hand, when receiving the transmission timing pulse from the transmission timing generation circuit 2, the counter 8
As shown in (e), counting of the clock pulse of the oscillator 1 is started.

When the ultrasonic wave transmitted from the transmitting transducer 4 is received by the receiving ultrasonic transducer 5, the received wave signal is transmitted via the receiving circuit 6 to the receiving timing detecting circuit 10 and the receiving wave sampling circuit 11. Sent to When the signal level of the received wave signal reaches a predetermined negative level as shown in FIG. 2A, the reception timing detection circuit 10 synchronizes the reception timing with the clock pulse as shown in FIG. Generate a pulse. This reception timing pulse is sent to the stop terminal of the counter 8 and the reception wave sampling circuit 11. Counter 8
When receiving this reception timing pulse,
As shown in (5), the counting of clock pulses is stopped.

On the other hand, upon receiving the reception timing pulse from the reception timing detection circuit 10, the reception wave sampling circuit 11 sequentially samples the reception wave signal using a clock pulse as shown in FIG. A / D converter 1 converts the sampling values of points P _{1 to} P ₄
After conversion into digital data in step 2, the data is sent to the microcomputer 9. The microcomputer 9 stores the sent sampling data in a memory or the like,
First, sampling points P ₁ and P _{2 at} which the sign of the data is inverted from the negative side to the positive side are selected. Then, as shown in FIG. 3, determined by linear interpolation using the straight line connecting the two points P _1, P ₂ linear equation, P from the interpolation straight line and the zero-crossing point and line intersect the signal level 0 P _c ' the time t _c until ₁ position is calculated by proportional calculation.

Then, the microcomputer 9 calculates the elapsed time T _m obtained from the count value m of the counter 8 =
Course of the (Δt × m), the elapsed time Delta] t from the reception timing pulse to the point P ₁ position, and a calculation time t _C obtained by the interpolation process, to the zero-cross point P _C 'position from the transmission timing pulse position Time (T _m + Δt +
After calculating t _C ), the elapsed time (T _m + Δt +
By subtracting one cycle time ΔT of the transmission frequency of the ultrasonic wave from t _C ), the final correct measurement time T ₀ =
Output as (T _m + Δt + t _C ) −ΔT.

When the position of the zero-cross point P _C ′ is obtained by the interpolation processing as described above,
The position of _C ′ can be accurately calculated as a time smaller than one clock width of the clock pulse. For this reason,
Although the clock pulse used is 1 MHz, which is the same as the conventional one, it is possible to further divide the 1 MHz pulse into smaller pieces for measurement, thereby improving the time resolution. This time resolution is determined by the A / D converter 1
2, for example, about 1/50 of the pulse width Δt of one clock pulse for 8 bits,
With 12 bits, a time resolution of about 1/800 can be obtained.

In the above example, the zero cross point P _c '
Is obtained by linear interpolation using two points P ₁ and P ₂ , but it is also possible to perform interpolation using a higher-order function such as secondary interpolation using three points and tertiary interpolation using four points. in this way,
The more you interpolation using a high-order function, the actual position error between the zero-cross point P _C and zero-cross point P _C 'determined by interpolation as shown in FIG. 3 is reduced, it is possible to realize a more highly accurate measurement .

[0022] In the above example, in order to simplify the explanation, the sampling frequency of the transmission timing pulse position to the P ₁ position shows the case of one (Fig. 2), from the transmission timing pulse position sampling times of up to P ₁ position is to vary depending on whether the first sampling point where the sign of the sampled data is changed from negative to positive is in any position. Thus, in general, when the sign of the positive changes sampling points from a negative and P _j, the elapsed time from the transmission timing pulse position to the sampling point P _j position where the code changes is (Delta] t ×
j).

Note that the time measuring circuit according to the present invention is applicable to a case where the ultrasonic wave transmitted from the transmitting transducer 4 is directly received by the receiving transducer 5 arranged opposite to the transmitting ultrasonic transducer.
The present invention can be applied to any use mode such as a case where a reflected wave of an ultrasonic wave transmitted from the transmission transducer 4 from an object to be detected is received by the reception transducer 5.

[0024]

As described above, when the time measuring circuit of the present invention is used, the position of the zero-cross point of the received wave signal is obtained by the interpolation processing, and the zero-cross point of the received wave signal obtained by this interpolation processing is received. The elapsed time from transmission to reception of the ultrasonic wave is calculated using the elapsed time to the timing pulse position and the elapsed time obtained by the counter, so that the time resolution is equal to or less than one clock pulse of the clock pulse of the oscillator. It is possible to increase the resolution and improve the measurement accuracy.
Further, since an expensive oscillator or counter having a high transmission frequency is not required to increase the resolution, the cost can be reduced and the power consumption can be reduced. Further, since there is no need to worry about clock noise, the degree of freedom in circuit design can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of a time measurement circuit according to the present invention.

FIG. 2 is a time chart of the time measurement circuit of FIG. 1;

FIG. 3 is an explanatory diagram of an interpolation process according to the present invention.

FIG. 4 is a block diagram of a conventional time measurement circuit.

FIG. 5 is a time chart of a conventional time measurement circuit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 oscillator 2 transmission timing generation circuit 3 transmission circuit 4 transmission ultrasonic transducer 5 reception ultrasonic transducer 6 reception circuit 8 counter 9 microcomputer (computing means) 10 reception timing detection circuit 11 reception wave sampling circuit 12 A / D converter

Claims (1)

[Claims] In a time measuring circuit for measuring an elapsed time from transmission to reception of an ultrasonic wave by counting clock pulses output from an oscillator, a signal level of a received wave signal of the ultrasonic wave reaches a predetermined level. A reception timing detection circuit that generates a reception timing pulse at a time, and a counter that starts counting clock pulses from an ultrasonic transmission start position and stops counting when a reception timing pulse is output from the reception timing detection circuit, A reception wave sampling circuit for starting sampling of a reception wave signal using a clock pulse from the time when the reception timing pulse is output from the reception timing detection circuit; and converting the sampling signal output from the reception wave sampling circuit into digital data. A / D converter Based on the sampling data sent from the A / D converter, a zero-cross point of the received wave signal is obtained by interpolation processing, A time measuring circuit comprising: an arithmetic unit that calculates an elapsed time from transmission to reception of an ultrasonic wave by using an elapsed time to a position.