JP2002196024A - Period measuring circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a period measurement with favorable accuracy even when an oscillation frequency of a clock device generating a reference frequency shifts from a center value. SOLUTION: A signal converting circuit 6 converts an input signal of a measurement object into a pulse signal with a pulse width corresponding to a period of the input signal, a first timer 50a counts the pulse width using a timer period generated on the basis of the reference frequency generated by the clock device 7, and a microcomputer 50 calculates the period of the input signal using the count value. A reference signal converting circuit 11 converts a commercial power source frequency into a pulse signal with a pulse width corresponding to period of a commercial power source 1, a second timer 50b counts the pulse width using the timer cycle, and the microcomputer 50 determines whether the commercial power source frequency is 50 Hz or 60 Hz from the count value and corrects the calculated period of the input signal on the basis of the determined frequency. By this, more accurate period can be measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a period measuring circuit for measuring the period of an input signal, and more particularly to a period measuring circuit using a timer.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing the configuration of a conventional cycle measuring circuit, FIG. 5 is a flowchart showing the operation of the cycle measuring circuit of FIG. 4, and FIG. 6 shows signals of various parts in FIG. It is a time chart.

In FIG. 4, 1 is a commercial power supply, 2 is a power supply circuit for generating an operating power supply for a microcomputer or the like,
Reference numerals 3 and 4 denote power supplies generated by the power supply circuit 2, 3 denotes a positive power supply of, for example, + 5V, and 4 denotes a GND. Reference numeral 5 denotes a built-in timer 5a for counting the period of the input signal based on a reference frequency generated by a clock device 7 described later, and a microcomputer for calculating the period (hereinafter abbreviated as "microcomputer"). A signal conversion circuit 7 converts the signal level into a signal level that can be counted by the microcomputer 5. A clock device 7 generates a reference frequency when the microcomputer 5 operates. The clock device 7 includes an oscillation element 8 such as a ceramic oscillator, a capacitor 9, and a feedback resistor 10. It is connected to the microcomputer 5.

Next, the operation of the cycle measuring circuit formed as described above will be described with reference to FIGS. (1) The input signal (FIG. 6-A) to be subjected to the cycle measurement is converted into a signal whose period can be measured by the input timer 5a to the signal conversion circuit 9 into, for example, a 0-5V pulse signal (FIG. 6-B). . (2) The converted pulse signal is input to the timer 5a.

(3) The timer period of the timer 5a is a period (FIG. 6-D) obtained by dividing the reference frequency (FIG. 6-C) inputted from the clock device 7, and the timer 5a is determined by the timer period. , From the rising edge of the pulse signal to the rising edge. The falling edge may be counted from the falling edge, or the falling edge may be counted from the rising edge.

(4) The microcomputer 5 periodically or irregularly measures the input signal using the timer cycle of the timer 5a (step 101).
It is checked whether the upper limit of the count number that can be counted has overflowed (step 102). (5) If it is confirmed that the timer 5a is in the overflow state, the cycle measurement is stopped and the overflow is stopped.
Is shifted to another routine determined in advance (step 103). Here, the contents executed by the routine to which the routine is transferred in step 103 are different depending on the device in which the period measurement circuit is used, and the operation of the period measurement circuit itself is not relevant. Omitted.

(6) If it is confirmed in step 102 that the timer 5a is not overflow, the count of the timer 5a is read. (Step 104) (7) The cycle of the input signal is calculated by the following equation (1) based on the read count number of the timer 5a and the timer frequency (Step 105).

T = m / f (1) T: cycle measurement value (second) m: pulse width count number by timer 5a (times) f: timer frequency (Hz) = 1 / timer cycle (A value defined in advance by the software of the microcomputer 5, for example,
When a timer obtained by dividing the reference frequency of 10 (MHz) of the oscillation circuit by 8 is used, it is defined as 1.25 (MHz). )

[0009]

The conventional cycle measuring circuit is constructed as described above. The reference frequency generated by the clock device 7 is incorporated in the microcomputer 5 due to the variation in the components of the oscillation element 8 used. If the value deviates from the specified value due to the matching between the circuit and the oscillation pendulum 8, the change due to the ambient temperature of the oscillation element 8, and the aging of the oscillation element 8, the timer frequency of the timer 5a for dividing the reference frequency is set in advance by the microcomputer. 5 is different from the value defined by the software of the microcomputer 5, the count number measured by using the timer 5a is different from the count number measured by the cycle of the software of the microcomputer 5 in advance. As a result, the measured value obtained from the count number counted by the timer 5a, which is obtained by dividing the frequency deviated from the frequency defined by the microcomputer 5 from the prescribed value, by the timer 5a, shows that the reference frequency of the oscillation element 7 deviates from the prescribed value. There has been a problem that the period is deviated from the regular period by the ratio.

For example, when the reference frequency of the oscillation element has a center value of 1
0 (MHz), the frequency (f) of the timer 5a is 1.25 which is a frequency division of the reference frequency 10 (MHz) of the oscillation element 7 by 8
(MHz), when the input signal is 50 (Hz), the timer 5
The count number by a is 1.25 (MHz) / 50 (MH)
z) = 25000.

However, when a certain type of ceramic resonator is used for the oscillation element 7, for example, the variation of the components of the oscillation element used is ± 0.5%, and the oscillation NAND circuit built in the microcomputer is used. Oscillator matching characteristics ± 0.4
%, The change in ambient temperature of the oscillation element is ± 0.4%, and the change over time of the oscillation element is ± 0.3%, and the total is ± 1.6%.
Will shift.

Using this oscillator, an input signal 50 (MH)
When the cycle measurement of z) is performed, the frequency of the timer 5a is 1
Since 0 (MHz) × 1.016 / 8 = 1.27 (MHz), the number of counts (times) by the timer 5a is 1.2
7 (MHz) / 50 (Hz) = 25400 (times), and the cycle measurement value (T) is: T = m / f = 25400 (times) /1.25 (Hz) =
0.020302 (seconds) = 49.21 (Hz), and while the input signal is 50 (Hz),
This results in an error of 1.6 (%).

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and focuses on the fact that the frequency of a commercial power supply is relatively stable. It is an object of the present invention to provide a cycle measuring circuit that can accurately measure a cycle even when a reference frequency of an element deviates from its center value.

[0014]

According to a first aspect of the present invention, there is provided a period measuring circuit for measuring a period of an input signal based on a reference frequency generated by a clock device. And a means for correcting the cycle of the input signal based on the frequency of the input commercial power supply.

The period measuring circuit according to a second aspect of the present invention is a period measuring circuit for measuring a period of an input signal, wherein the period measuring circuit measures a period of the input signal based on a reference frequency generated by a clock device. Means for correcting the cycle of the input signal based on a predetermined frequency of the commercial power supply.

According to a third aspect of the present invention, there is provided a cycle measuring circuit for measuring a cycle of an input signal, comprising: a clock device for generating a reference frequency; and a clock having a pulse width corresponding to the cycle of the input signal. A first signal conversion circuit for converting the first pulse signal into a first pulse signal; and a first signal conversion circuit for counting a period of a pulse width of the first pulse signal based on the reference frequency.
A timer for calculating the period of the input signal based on the count value; a second signal conversion circuit for converting a second pulse signal having a pulse width corresponding to a period of the commercial power supply; A second timer for counting a period of a pulse width of the pulse signal based on the reference frequency;
And a period correcting means for determining the frequency of the commercial power supply based on the count value of the timer, and correcting the calculated period of the input signal based on the determined frequency.

According to a fourth aspect of the present invention, there is provided a cycle measuring circuit for measuring a cycle of an input signal, comprising: a clock device for generating a reference frequency; and a clock having a pulse width corresponding to the cycle of the input signal. A first signal conversion circuit for converting the first pulse signal into a first pulse signal; and a first signal conversion circuit for counting a period of a pulse width of the first pulse signal based on the reference frequency.
And a calculating means for calculating the cycle of the input signal based on the count value, and a cycle correcting means for correcting the cycle of the calculated input signal based on a predetermined frequency of the commercial power supply. It is.

According to a first aspect of the present invention, there is provided a cycle measuring circuit according to the first or second aspect, wherein the input signal measured based on a reference frequency when the input signal to be measured is a commercial power supply. Cycle and commercial power cycle
When (reciprocal of frequency) is within a predetermined range, the cycle of the input signal measured based on the reference frequency is adopted.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a block diagram showing a circuit configuration of a cycle measuring circuit according to the first embodiment of the present invention, FIG. 2 is a flowchart showing an operation of the cycle measuring circuit shown in FIG. 1, and FIG. It is a time chart shown.

In FIG. 1, 1 is a commercial power supply, 2 is a power supply circuit for generating a power supply for operation of a microcomputer or the like,
Reference numerals 3 and 4 denote power supplies generated by the power supply circuit 2. Reference numeral 3 denotes a positive power supply of, for example, + 5V, and reference numeral 4 denotes GND. Reference numeral 50 denotes a built-in first timer 50a for counting the period of an input signal based on a reference frequency generated by a clock device 6 described later, and a microcomputer for calculating the period (hereinafter abbreviated as a microcomputer). Is a signal conversion circuit that converts the signal level into a signal level that can be counted by the timer 50a.

Reference numeral 7 denotes a clock device for generating a reference frequency when the microcomputer 50a operates. The clock device 7 includes an oscillation element 8, such as a ceramic oscillator, a capacitor 9, and a feedback resistor 10, and is connected to the microcomputer 50. Reference numeral 11 denotes a second timer 50 in which the voltage of the commercial power supply is built in the microcomputer 50.
Reference signal conversion circuit 51 converts the signal level into a pulse signal of, for example, 0-5 V, which can be measured at the period b. Reference numeral 51 denotes a correction switch connected to microcomputer 50 to execute correction at an arbitrary time.

Next, the operation will be described with reference to FIGS. (1) A period from the rising edge to the rising edge of the pulse signal (FIG. 3-B) obtained by converting the voltage of the commercial power supply 1 (FIG. 3-A) by the reference signal conversion circuit 11 regularly or irregularly is defined as a second section. Is counted using the timer 50b.
(Step 200). The falling edge may be counted from the falling edge, or the falling edge may be counted from the rising edge.

(2) As a result of counting, the second timer 50
It is determined whether or not b has overflown (step 201). If the second timer 50b has overflown, the period measurement is stopped and the timer overflows. −
The flow shifts to another routine predetermined for the flow (step 201). Note that the contents executed by the routine at the transition destination in step 103 are different depending on the device in which the cycle measuring circuit is used, and the operation of the cycle measuring circuit itself is irrelevant, so that the description is omitted.

(3) As a result of counting, the second timer 50
If b does not overflow, the microcomputer 50
Reads the count number of the second timer 50b and reads
Is stored in a RAM (random access memory) (not shown) built in the CPU. (Step 202) (4) Whether the frequency of the commercial power supply is 50 (Hz) based on the count number of the second timer 50b read from the RAM,
It is determined whether the frequency is 60 (Hz) (step 203).
The threshold value is, for example, 50.5 (Hz). When the value is equal to or greater than the threshold value, 60 (Hz), and when the value is equal to or less than the threshold value, 50 (H).
z) is determined.

For example, if the reference frequency (FIG. 3-C) is 10
Timer frequency obtained by dividing the reference cycle by 8 in (MHz).
As a result of measuring the cycle of the commercial power using f (1.25 MHz), the count number (m1) of the second timer 50b is 2
Reference signal cycle measurement value (T1) for 4800 (times)
Is calculated by equation (2). T1 = m1 / f ---------------- (2) = 24800 (times) /1.25 (MHz) = 0.019
84 (sec), and 0.01984 (sec) is equivalent to 50.40 Hz, and 50.40 (Hz) <50.5 (Hz). Therefore, the commercial power supply in this case is determined to be 50 (Hz). .

(5) The timer cycle of the first timer 50a is corrected using the frequency based on the above judgment (step 204). Note that the correction timer cycle (1 / timer frequency) is derived as follows. f1 = (m1 × n1) / C ――――――――― (3) f2 = f1 / n2 ――――――――― (4) f1: Correction reference frequency f2: Correction timer frequency m1: Count number by the second timer 50b n1: frequency division number of the second timer 50b C: commercial power supply cycle n2: frequency division number of the first timer 50a

For example, the frequency of the commercial power supply obtained in (4) is 50 (Hz), and the count number (m1) obtained by counting the cycle of the commercial power supply by the second timer 50b is 248.
00, the correction reference frequency (f1) when the frequency division number (n1) of the second timer 50b is 8 is: f1 = (8 × 24800) /1/50=9.92 (MH
z) 9.92 (MHz) corresponds to 1.008 × 10 ⁻⁶ (second).

The correction timer frequency (f2) of the first timer 50a is calculated by dividing the frequency (n2) of the first timer 50a.
Is set to 8, f2 = f1 / n2 = 9.92 / 8 = 1.
24 (MHz).

(6) Periodically or irregularly, the microcomputer 50 performs a period measurement using the timer period of the first timer 50a (FIG. 6-D) (step 101). (7) When the cycle measurement is completed, it is checked whether or not the upper limit of the count number that can be counted by the first timer 50a has overflowed (step 102). (8) When it is confirmed that the first timer 50a is in the overflow state, the cycle measurement is stopped, and another predetermined timer for the overflow is determined. -Transfer to the chin (step 103). Here, step 1
The contents executed by the routine of the migration destination of 03 differ depending on the device in which the cycle measurement circuit is used,
Since the operation of the cycle measuring circuit itself has no relation, the description is omitted.

(9) First timer 5 in step 102
When it is confirmed that 0a is not an overflow, the count number of the first timer 50a is read. (Step 104) (10) The period (T) of the input signal is calculated by the equation (5) using the read count number of the timer n50a and the correction timer frequency (f2) derived above (Step 10).
5). T = m / f2 ――――――――― (5) T: cycle measurement value (second) m: count number by the first timer 50a (times) f 2: correction timer frequency (in the above example, 1.24MH
z)

As described above, for example, when a ceramic resonator is used for the oscillation element 8, the variation of the components of the oscillation element to be used (± 0.5%) and the oscillation NAND circuit built in the microcomputer And oscillator matching characteristics (± 0.
4%), an ambient temperature change of the oscillation element (± 0.4%), an aging change of the oscillation element (± 0.3%), etc., the maximum of ± 1.6% of the error corresponds to the cycle measurement value. However, according to the present invention, the frequency accuracy of the commercial power supply is ± 0.2 Hz (± 0.4% at 50 Hz, 60 Hz).
Since the period measurement is performed within the error of ± 0.33% at z, the accuracy can be improved by about 1.2%.

In the above embodiment, the first timer 5
The description has been given of the case where the correction of the timer cycle of 0a is performed periodically or irregularly according to the software preset in the microcomputer 50. However, the correction may be performed by turning on the external switch 51 at an arbitrary time.

In the above embodiment, a description is given of a case where the frequency is determined and the timer cycle of the first timer 50a is corrected in a cycle measuring circuit applicable to a commercial power supply of either 50 Hz or 60 Hz. However, the present invention can also be applied to a commercial power supply having a predetermined frequency. In this case, the step 203 of determining the frequency of the commercial power supply is unnecessary, and the timer cycle of the first timer 50a is set to a predetermined frequency. What is necessary is just to correct it.

Embodiment 2 In the first embodiment, the cycle of the input signal is corrected with the frequency of the commercial power supply. However, in the second embodiment, when the input signal to be measured is the cycle of the commercial power supply, the cycle of the measured input signal and the frequency of the commercial power supply are corrected. When the period (the reciprocal of the frequency) is not so different, or when the ratio between the two is very small, the correction by the frequency with the commercial power supply is not performed, and the period of the input signal before the correction is adopted.

From the following equation shown in the first embodiment, f1 = (m1 × n1) / C (3) f2 = f1 / n2 (4) T = m / f2 ------ (5) f2 = (m1 × n1) / C / n2 = (m1 × n1) / n
2 · CT = m / [(m1 × n1) / n2 · C] = m · n2 · C / (m1 × n1) (6)

Since the frequency division numbers of the first and second timers are the same (8 in the first embodiment), n2 = n1, and the equation (6) becomes T = m.C / m1. (7) and the corrected cycle is the ratio of the count numbers of the first and second timers. Therefore, if m1 = 24800 and m = 24801, T1 in the above equation (1) is not corrected.
= M / f is adopted as it is.

As described above, when m-m1 is within a predetermined range (for example, within ± 10 counts), or the ratio of both is within a predetermined range (for example, within ± 0.1%). In this case, the correction calculation is not performed, and the cycle is calculated by adopting the correction as it is. In this way, the calculation speed is high,
The burden on the CPU is also reduced. Note that the correction calculation is not performed when m = m1, but the correction calculation may not be performed in this case also in the first embodiment.

[0038]

As described above, according to the present invention, even when an error occurs in the reference frequency, for example, when a period measurement is performed using an oscillator having poor oscillation frequency accuracy, the frequency of the commercial power By correcting based on
An accurate period measurement circuit can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a period measurement circuit according to Embodiment 1 of the present invention.

FIG. 2 is a flowchart showing an operation of period measurement of FIG. 1;

FIG. 3 is a time chart showing signals of respective parts in FIG. 1;

FIG. 4 is a block diagram of a conventional cycle measuring circuit.

FIG. 5 is a flowchart showing an operation of period measurement of FIG. 4;

FIG. 6 is a time chart showing signals of respective parts in FIG. 5;

[Explanation of symbols]

1 commercial power supply, 2 power supply circuit, 6 signal conversion circuit, 7
Clock device, 8 oscillation element, 11 reference signal conversion circuit, 50 microcomputer, 50a first timer, 50b second timer, 51 correction switch.

Claims (5)

[Claims] 1. A cycle measuring circuit for measuring a cycle of an input signal, comprising: means for measuring a cycle of the input signal based on a reference frequency generated by a clock device; A cycle measuring circuit comprising means for correcting a cycle. 2. A cycle measuring circuit for measuring a cycle of an input signal, comprising: means for measuring a cycle of the input signal based on a reference frequency generated by a clock device; A period measuring circuit comprising means for correcting the period of the period. 3. A cycle measuring circuit for measuring a cycle of an input signal, a clock device for generating a reference frequency, and a first signal conversion circuit for converting the input signal into a first pulse signal having a pulse width corresponding to the cycle of the input signal. A first timer that counts a period of the pulse width of the first pulse signal based on the reference frequency; a calculating unit that calculates a cycle of the input signal based on the count value; A second signal conversion circuit for converting a pulse width of the second pulse signal into a second pulse signal, a second timer for counting a period of the pulse width of the second pulse signal based on the reference frequency, and the second timer A period correction means for determining the frequency of the commercial power supply based on the count value of the above, and correcting the period of the calculated input signal based on the determined frequency. Measuring circuit. 4. A cycle measuring circuit for measuring a cycle of an input signal, a clock device for generating a reference frequency, and a first signal conversion circuit for converting the input signal into a first pulse signal having a pulse width corresponding to the cycle of the input signal. A first timer for counting a period of a pulse width of the first pulse signal based on the reference frequency; a calculating means for calculating a cycle of the input signal based on the count value; A period correction unit for correcting the period of the input signal calculated based on the frequency of the period. 5. The cycle measuring circuit according to claim 1, wherein, when the input signal to be measured is a commercial power supply, a cycle of the input signal measured based on a reference frequency and a cycle of the commercial power supply (reciprocal of frequency). A period of the input signal measured based on the reference frequency, when the period is within a predetermined range.