JPH11118854A - Pulse width measuring circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pulse width measuring circuit capable of high-accuracy pulse width measurements by use of a circuit element providing relatively low frequency performance. SOLUTION: A signal S1 matching the width of an input pulse is obtained from a control part U1 and a capacitor C is charged using a constant current source 1a to obtain a charging voltage proportional to the pulse width. Then the discharge of the capacitor C is started from a constant current source 1b in response to a signal S2, and a counter U2 starts counting the clocks of a reference clock generator U3 and, when a comparator U4 detects the end of the discharge, stops the counting. Therefore, the counting period of the counter relative to the input pulse width is increased to match the current ratio of the constant current sources 1a and 1b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a pulse width measuring circuit for obtaining a pulse width of a pulse signal as a count value of a counter.

[0002]

2. Description of the Related Art As shown in FIG. 3, a pulse width measuring circuit provided in various processing / control devices utilizing a pulse signal uses a counter C at a leading edge of an input pulse signal.
NT starts counting the reference clock signal φ, stops counting the reference clock signal φ at the trailing edge of the input pulse signal, and there is a counter CNT at this time that obtains a count value proportional to the width of the input pulse signal. .

[0003]

The conventional pulse width measuring circuit has the following problems.

(1) Since the resolution of the measurement depends on the frequency of the reference clock φ, high-precision measurement less than the period of the reference clock φ cannot be performed. In addition, short pulses cannot be measured.

(2) To increase the resolution, a high-frequency pulse generator is prepared for the reference clock φ, and the counter CNT is provided.
In order to prepare a circuit having a high-frequency pulse counting capability, an advanced circuit technology is required, and an expensive measuring circuit is required.

SUMMARY OF THE INVENTION An object of the present invention is to provide a pulse width measuring circuit capable of measuring a pulse width with high accuracy using a circuit element having a relatively low frequency performance.

[0007]

According to the present invention, a capacitor is charged and discharged by two types of constant current sources, a current ratio of the charging and discharging is taken out as a time width, and a counter counts a reference clock in this time width. By extending the counting period of the counter with respect to the input pulse width according to the current ratio of the two types of constant current sources, the input pulse width can be measured with high resolution using circuit elements having relatively low frequency performance. Which is characterized by the following configuration.

A pulse width measuring circuit for obtaining a width of an input pulse signal as a count value of a counter, wherein charging of a capacitor is started from an initial state by a first constant current source at a leading edge of the input pulse, and a trailing edge of the input pulse is measured. And discharging the capacitor by means of a second constant current source, and a counter means for counting a reference clock only during a discharging period from the start of discharging of the capacitor to the initial state.

The circuit means varies the current ratio between the first constant current source and the second constant current source.

[0010] The circuit means measures the time width of the reference clock and corrects the count value of the counter.

[0011]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. The input pulse is input to the control unit U1 as the width T1. After releasing the reset of the counter U2 by inverting the reset signal of the counter U2 at the leading edge of the input pulse, the control unit U1 generates an S1 signal having a pulse width between the time T1 and the synchronization, and generates the S1 signal. The S2 signal is generated at the timing of the trailing edge.

The constant current sources Ia and Ib generate a current having a determined current ratio Ia: Ib, and charge and discharge the capacitor C according to the S1 signal and the S2 signal. Prior to the charging / discharging, the control unit U1 generates a signal S3 to change the capacitor C from a short-circuit (complete discharge) state to a charge preparation state (initial state).

The comparator U4 inverts the output when the voltage of the capacitor C exceeds the reference voltage (ground) by charging the capacitor C, and returns from the inversion state when the voltage reaches the reference voltage by discharging the capacitor C. I do.

After the resetting by the control unit U1, the counter U2 sets the signal S2 as a count start signal (counter start signal) and sets the return signal of the comparator U4 as a count stop signal (counter stop signal). The reference clock φ from the reference clock generator U3 is counted.

The pulse width measuring operation according to the above configuration is shown in a time chart shown in FIG. Before starting measurement,
The voltage of the capacitor C is set to the initial state by the signal S3 from the control unit U1, and preparation for charging is made.

In this state, when an input pulse is applied to the control unit U1, when the S1 signal from the control unit U1 is turned on, the voltage Vc across the capacitor C becomes constant current source Ia
Start rising by charging from.

Thereafter, when the control unit U1 turns off the signal S1 after the lapse of the pulse width period T1 of the input pulse, the capacitor C reaches a charging voltage proportional to the period T1. In this state, the control unit U1 turns off the signal S1 and simultaneously outputs the signal S2.
Is turned on, the capacitor C starts discharging by the constant current source Ib and starts falling, and at the same time, the counter U2 starts counting the clock φ from the reference clock generator U3.

Thereafter, when the voltage of the capacitor C reaches the reference voltage (ground), the output of the comparator U4 is inverted,
With this inversion, the counter U2 stops the counting operation.

Here, for example, between the current sources Ia and Ib,
If there is a relation of Ia = 10 × Ib, the comparator U4
, The relationship between T2 and T1 is T1 × 10: T
2, T2 represents ten times the time of T1, and the time measured by the counter U2 is expanded to ten times the period of the input T1.

For this reason, the frequency of the reference clock generator U3 may be 1/10 of the resolution of the measured value. In order to improve the resolution, it is only necessary to change the ratio of the constant current sources Ia and Ib, and it is possible to easily obtain a resolution of about 100 to 1000 times. There is no need to improve the counting performance of U2.

In the above embodiment, the constant current source I
Although a and Ib are fixed, a variable constant current source that digitally changes the current ratio using, for example, a ladder resistor or the like may be used. In this case, Ia and Ib are arbitrary, and the programmable pulse width of the resolution is used. It can be a measurement circuit.

Further, in the embodiment, although the accuracy of the reference clock directly becomes a measurement error of the pulse width, the path a in FIG. 1 is provided, and the control unit U1 measures the reference clock.
The measured value can be corrected by the value. In this case, a pulse width measurement circuit that is not affected by the accuracy of the reference clock can be realized.

Further, the configuration of each part in the embodiment can be appropriately changed in design.

[0024]

As described above, according to the present invention, a capacitor is charged and discharged by two types of constant current sources, the current ratio of the charging and discharging is taken out as a time width, and the counter counts the reference clock in this time width. As a result, a count value proportional to the pulse width is obtained, so that there is an effect that the input pulse width can be measured with high resolution using a circuit element having a relatively low frequency performance. Specifically, the following effects are obtained.

(1) Even when measuring a short pulse width, a high-speed reference clock is not required, and a counter having a high-speed performance is not required.

(2) The resolution of the measured value can be easily changed.

(3) The measurement accuracy can be improved by measuring the reference clock.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a time chart in the embodiment.

FIG. 3 is a configuration diagram of a conventional pulse width measurement circuit.

[Explanation of symbols]

 U1: control unit U2: counter U3: reference clock generator U4: comparator C: capacitors Ia, Ib: constant current source

Claims (3)

[Claims] 1. A pulse width measuring circuit for obtaining a width of an input pulse signal as a count value of a counter, wherein charging of a capacitor from an initial state is started by a first constant current source at a leading edge of the input pulse, and A pulse which starts discharging the capacitor by a second constant current source at a trailing edge, and wherein the counter counts a reference clock only during a discharging period from the start of discharging the capacitor to the initial state. Width measurement circuit. 2. The pulse width measuring circuit according to claim 1, wherein said circuit means changes a current ratio between said first constant current source and said second constant current source. 3. The pulse width measuring circuit according to claim 1, wherein said circuit corrects a count value of said counter by measuring a time width of said reference clock.