JP4466822B2 - Frequency measurement circuit - Google Patents

Description

  The present invention relates to a frequency measurement circuit for measuring a frequency applied to a signal under measurement with high speed and high resolution.

  When measuring various physical quantities, for example, when measuring pressure or differential pressure, a frequency signal is obtained from a vibration pressure sensor, and the corresponding physical quantity (frequency signal or differential pressure signal, etc.) It may be output as a 4-20 mA current signal.

  FIG. 4 is a functional block diagram showing the configuration of a conventional frequency measurement circuit that measures a frequency signal sent from a vibration type pressure sensor, and FIG. 5 is a timing chart showing an operation example.

  The vibration pressure sensor 21 outputs a frequency signal f having a frequency corresponding to the pressure to be measured. The frequency measurement circuit shown in this figure is a circuit that obtains the frequency (period) of the frequency signal f and outputs the pressure value to be measured.

  The synchronization circuit 23 outputs a synchronization signal F obtained by synchronizing the frequency signal f with the reference clock 22.

  As shown in FIG. 5, a rise time difference Δt (Δt (0), Δt (1)) shorter than one cycle of the reference clock 22 occurs between the frequency signal f and the synchronization signal F. The time difference detection circuit 24 detects this rise time difference Δt, and outputs a signal that is L level only during a period corresponding to the value, that is, a time difference signal Tin that is L level only during a period shorter than one cycle of the reference clock 22. .

  Returning to FIG. 4, the time width expansion circuit 25 outputs an expanded time difference signal Tout obtained by expanding the L level period of the time difference signal Tin by the expansion rate K.

  FIG. 6 shows an example of a specific circuit configuration of the general time width expanding circuit 25. The time width expansion circuit 25 uses the difference between the charging time and the discharging time of the capacitor C1 to increase the falling time width of the time difference signal Tin, which is an input signal, based on the resistances R1 and R2, and an expansion rate K = Enlarge with (R2 × R4) / (R1 × R3).

  Further, the time width expanding circuit 25 is configured to generate an expanded time difference having an L level period exceeding one period of the reference clock 22 in proportion to the L level period from a time difference signal Tin having an L level period of less than one period of the reference clock 22. The signal Tout is output.

  Returning to FIG. 4, the first counter 26 counts the time corresponding to the period of the synchronization signal F as the number of clock pulses of the reference clock 22.

  The second counter 27 counts the number of pulses of the reference clock 22 in a period corresponding to the rise time difference Δt expanded by the time width expansion circuit 25.

  The arithmetic circuit 28 calculates the period of the frequency signal f based on the count number of the first counter 26 and the count number of the second counter 27.

The period Tf of the frequency signal f is TF as the period of the synchronization signal F, Δt (0) as the rise time difference at the start of one period, and Δt as the rise time difference at the end of that period (at the start of the next period). If (1), as shown in FIG.
Tf = TF− (Δt (1) −Δt (0))
It is represented by

That is, the period Tf of the frequency signal f corresponds to the count number A (A (1)) of the first counter 26 in the period corresponding to the period TF of the synchronization signal F and the rise time difference Δt (0) at the start of the period. The count number B (0) of the second counter 27 during the period to be used and the count number B (1) of the second counter 27 during the period corresponding to the rise time difference Δt (1) at the end of the cycle,
Tf = Tref × {A− (B (1) −B (0)) / K}
(Where Tref is one cycle of the reference clock signal). Thus, in this frequency measurement circuit, the period Tf of the frequency signal f is repeatedly calculated.

  Such techniques are described in, for example, the following documents.

JP-A-5-157647 JP-A-6-274240 Japanese Patent Laid-Open No. 7-71979

  By the way, when such a frequency measurement circuit is used in an environment where the temperature change is severe, in the time width expansion circuit 25 as shown in FIG. 6, the resistance values of the resistors R1, R2, R3 and R4 are the temperature of the surrounding environment. It changes according to change.

  In this case, as the values of the resistors R1, R2, R3, and R4 change, the time expansion rate K of the time width expansion circuit 25 also changes due to the temperature change, and therefore corresponds to one period Tf of the frequency signal f. There is a problem that the calculated value fluctuates and the measurement accuracy decreases.

  Further, due to variations in the resistors R1, R2, R3, and R4, the time expansion width K varies depending on the individual time width expansion circuits 25. For this reason, at the time of manufacturing the frequency measurement circuit, there is a problem that a step of measuring and confirming the time expansion rate K of the time width expansion circuit 25 for each circuit is required.

  An object of the present invention is to provide a frequency measurement circuit that solves the above-described problems and can prevent a decrease in measurement accuracy even when the temperature change is severe.

  It is another object of the present invention to provide a frequency measurement circuit that does not need to measure the time expansion rate in advance even when the time expansion width of the time width expansion circuit varies individually.

Means for solving the above object are as follows.
(1) A time width expansion circuit (6) for synchronizing the frequency signal (f) of the vibration type pressure sensor (1) with a reference clock (2) and expanding the rise time difference between the synchronization signal and the frequency signal (f). Then, a physical quantity corresponding to the frequency signal (f) is calculated from a value obtained by counting the synchronization signal by the reference clock (2) and a value obtained by counting the output of the time width expansion circuit by the reference clock (2). An arithmetic circuit (10), a first calibration signal (CALin (1)) having a period that is an integer (p) times the period of the reference clock (2), and an integer (q) times the reference clock (2). A second calibration signal (CALin (2)) having a period longer than that of the first calibration signal (CALin (1)) is used as the time width expansion circuit (6). A calibration pulse generation circuit (5) to output and a signal corresponding to the first calibration signal (CALin (1)) via the time width expansion circuit (6) are counted according to the reference clock (2). One count number (C (1)) and a second count number (C (2) obtained by counting a signal corresponding to the second calibration signal via the time width expansion circuit (6) according to the reference clock (2). )), And the arithmetic circuit (10) is based on the difference between the second count number (C (2)) and the first count number (C (1)). A frequency measurement circuit for a vibration type pressure sensor, wherein the physical quantity is calculated.
(2) The time width expanding circuit is characterized in that a signal relating to a rise time difference between the synchronization signal and the frequency signal and a signal from the calibration pulse generation circuit are switched and input in a time division manner (1) ) Frequency measurement circuit as described.
(3) The calibration pulse generation circuit generates a first calibration signal at a time near the middle of the m-th cycle (m is an integer) and the m + 1-th cycle from the start of measurement, and the m + 1-th cycle and the (m + 2) -th cycle. The frequency measurement circuit according to (1) or (2), wherein the second calibration signal is generated at a time near the middle of the period.
(4) The arithmetic circuit calculates an actual enlargement ratio from the count value applied to the first calibration signal and the count value applied to the second calibration signal. (1) to (3) The frequency measurement circuit according to any one of the above .

  According to the frequency measurement circuit of the present invention, a calibration pulse having a pulse width corresponding to n periods (n is a natural number) of the reference clock is input to the time width expansion circuit, and the expanded pulse width is converted to the clock of the reference clock. Since the magnification of the time width expansion circuit is calibrated based on the count value counted according to the pulse, it is possible to prevent a decrease in measurement accuracy even when the actual magnification ratio of the time width expansion circuit varies from its design value. Even when the actual expansion rate of the time width expansion circuit varies individually, it is not necessary to measure the actual expansion rate in advance at the time of manufacture.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of a frequency measurement circuit according to an embodiment of the present invention.
This frequency measurement circuit is similar to the conventional frequency measurement circuit shown in FIG. 4, such as the vibration pressure sensor 1, the reference clock 2, the synchronization circuit 3, the time difference detection circuit 4, the time width expansion circuit 6, the first counter 7, In addition to a 2 counter 8 and an arithmetic circuit 10, a calibration pulse generation circuit 5 and a third counter 9 are further provided.

  The vibration type pressure sensor 1 is configured using, for example, a crystal resonator, and outputs a frequency signal f corresponding to the input pressure.

  The synchronization circuit 3 outputs a synchronized frequency signal F obtained by synchronizing the frequency signal f with the reference clock 2.

  The time difference detection circuit 4 detects a rise time difference Δt that is shorter than one cycle of the reference clock 2 and outputs a time difference signal Tin that becomes L level only during a period corresponding to the time difference.

  The calibration pulse generation circuit 5 outputs a first calibration signal CALin (1) that is L level only during a period corresponding to the p period (p is an integer, for example, one period) of the reference clock 2 and the reference clock 2 The second calibration signal CALin (2), which is at the L level only during a period corresponding to q periods (q is an integer, p ≠ q, for example, 2 periods), is output.

  The time width expansion circuit 6 has a circuit configuration similar to that of the general time width expansion circuit 25 shown in FIG. The time width expansion circuit 6 inputs the time difference signal Tin from the time difference detection circuit 4 and the calibration signal CALin of the calibration pulse generation circuit 5 in a time-sharing manner, and sets the L level period of the time difference signal Tin to an expansion rate K (design value). And an enlarged calibration signal CALout obtained by enlarging the L level period of the calibration signal CALin with an enlargement factor K.

  The first counter 7 receives the synchronization signal F and counts the number of pulses A (n) of the reference clock 2 for a time corresponding to the period.

  The second counter 8 receives the enlarged time difference signal Tout and counts the number of pulses B (n) of the reference clock 2 during the L level period.

  FIG. 2 shows an expansion of the L level period of the calibration signal CALin by the time width expansion circuit 6 as a timing chart.

  Returning to FIG. 1, the third counter 9 receives the reference clock 2 in the L level period of the first expanded calibration signal CALout (1) output from the time width expanding circuit 6 to which the first calibration signal CALin (1) is input. The number of clock pulses is counted as the first count number C (1).

  Furthermore, the third counter 9 receives the clock pulse of the reference clock 2 in the L level period of the second expanded calibration signal CALout (2) output from the time width expanding circuit 6 to which the second calibration signal CALin (2) is input. The number is counted as the second count value C (2).

  Here, if p = 1 and q = 2 are set, and the actual magnification rate of the time width expansion circuit 6 is K ′, the L level period of the first calibration signal CALin (1), 2 Since the difference between the calibration signal CALin (2) and the L level period is one cycle (qp = 1) of the reference clock 2, the actual enlargement ratio K ′ is accompanied by a temperature change in the surrounding environment, etc. If there is no change, the difference between the second count number C (2) and the first count number C (1) coincides with the actual value of the enlargement factor K ′.

  The arithmetic circuit 10 uses the first count value C (1) and the second count value (2) as calibration data, and dynamically calculates the actual enlargement ratio K ′ of the time difference enlargement circuit 6.

  FIG. 3 is a diagram illustrating the calculation of the period of the frequency signal f and the output timing of the calibration signal CALin. For example, if the measurement of the frequency is started at time t0, the second counter 8 causes the arithmetic circuit 10 to send the rise time difference Δt (at the start of the first (first) cycle of the frequency signal f (synchronization signal F). A count number B (0) corresponding to 0) is output.

  The calibration pulse generation circuit 5 outputs the first calibration signal CALin (1) at a time near the middle between the start time t0 of the first cycle and the start time t1 of the second cycle, and the third counter 9 outputs the first count number C (1) described above.

  When the first cycle ends and the second cycle starts at time t1, the calibration pulse generation circuit 5 has a time near the middle between the start time t1 of the second cycle and the end time t3 of the cycle. The second calibration signal CALin (2) is output, and the third counter 9 outputs the second count number C (2).

  The arithmetic circuit 10 measures the actual enlargement ratio K ′ using the first count number C (1) and the second count number C (2). Specifically, the actual enlargement ratio K ′ is obtained by K ′ = C (2) −C (1).

In this frequency measurement circuit, in the cycle of n (n: a natural number of 2 or more) from the start of measurement, the count number B (n−1) of the second counter 8 at the start of the cycle and the end of the cycle Based on the count number A (n) of the first counter 7 and the count number B (n) of the second counter obtained at times, and the count numbers C (1) and C (2) of the third counter by the nth cycle Based on the actual magnification K ′ measured in
Tf (n) = Tref × {A (n) − (B (n) −B (n−1)) / K ′}
(Where K ′ = C (2) −C (1), Tref is one cycle of the reference clock signal), the cycle of the frequency signal f can be obtained.

  In the example of FIG. 3, the third counter 9 counts the first count number C (1) again at a time near the middle between the m-th cycle and the m + 1-th cycle from the start of measurement, and the m + 1-th cycle. And the second count number C (2) is counted at a time near the middle of the m + 2th cycle, and the actual enlargement ratio K ′ is updated.

  In this example of the present embodiment, when the frequency signal f is measured, the count number C of the third counter is used as calibration data, and the actual magnification K ′ of the time width expansion circuit 6 is calibrated at a predetermined cycle. Even when the actual enlargement ratio K ′ fluctuates from the design value K due to a temperature change in the surrounding environment, it is possible to prevent a decrease in measurement accuracy.

  In addition, since the actual magnification rate K ′ of the time width expansion circuit 6 is measured when the frequency signal f is measured, a process for measuring and adjusting the time magnification rate in advance is not necessary when the frequency measurement circuit is manufactured. .

  In the above embodiment, the L level period of the first calibration signal CALin output from the calibration pulse generation circuit 5 is a period corresponding to one cycle (p = 1) of the reference clock signal, and the second calibration. Although an example in which the L level period of the signal CALin is a period corresponding to two periods (q = 2) of the reference clock signal has been shown, the L level period of the calibration signal CALin has a period that is a natural number multiple of the reference clock signal. The period is not limited to the above period as long as it corresponds to the period.

  For example, the L level period of the first calibration signal CALin is a time corresponding to one period (p = 1) of the reference clock signal, and the L level period of the second calibration signal CALin is three periods (q = 3), and the actual enlargement ratio K ′ can be calculated as K ′ = (C (2) −C (1)) / 2.

  Further, although an example has been shown in which the actual enlargement ratio K ′ of the time width expansion circuit 6 is calculated based on the first count number C (1) and the second count number C (2) output from the third counter 9. The actual enlargement ratio K ′ can also be calculated based on one of the first count number C (1) and the second count number C (2).

  For example, when obtaining the cycle of the frequency signal f of the first cycle shown in FIG. 3, the actual enlargement factor K ′ can be calculated as K ′ = C (1). When the second count number C (2) is used alone, the actual enlargement ratio K ′ can be calculated as K ′ = C (2) / 2.

  Further, in the above-described embodiment, an example in which the actual magnification rate K ′ of the time width expansion circuit 6 is measured at a predetermined period has been described. You may perform at the timing which the sensor detected the temperature change.

  In this case, if the temperature change in the surrounding environment is severe, calibrating the update interval of the actual enlargement factor K ′ can be calibrated to prevent a decrease in measurement accuracy, and if the temperature change is small, the frequency measurement cycle is shortened. Thus, highly accurate frequency measurement is possible.

  Although the present invention has been described based on the preferred embodiment, the frequency measurement circuit of the present invention is not limited to the above embodiment, and various modifications and changes can be made to the configuration of the above embodiment. A modified frequency measurement circuit is also included in the scope of the present invention.

It is a block diagram which shows the frequency measurement circuit of one example of embodiment of this invention. 6 is a timing chart showing the expansion of the L level period of the calibration signal CALin by the time width expansion circuit 6; It is a timing chart which shows the calculation of the period of the frequency signal f, and the output timing of the calibration signal CALin. It is a block diagram which shows the structure of the conventional frequency measurement circuit. 5 is a timing chart illustrating an operation example of the frequency measurement circuit illustrated in FIG. 4. It is a circuit diagram which shows the example of the circuit structure of a general time width expansion circuit.

Explanation of symbols

1,21 Vibrating pressure sensor 2,22 Reference clock 3,23 Synchronization circuit 4,24 Time difference detection circuit 5 Calibration pulse generation circuit 6,25 Time width expansion circuit 7,26 First counter 8,27 Second counter 9 First 3 counter 10, 28 arithmetic circuit

Claims (4)

A time width expansion circuit (6) for synchronizing the frequency signal (f) of the vibration type pressure sensor (1) with a reference clock (2) and expanding a rise time difference between the synchronization signal and the frequency signal (f);
An arithmetic circuit for calculating a physical quantity corresponding to the frequency signal (f) from a value obtained by counting the synchronization signal by the reference clock (2) and a value obtained by counting the output of the time width expansion circuit by the reference clock (2). (10) and
The first calibration signal (CALin (1)) having a cycle that is an integer (p) times the cycle of the reference clock (2), and a cycle that is an integer (q) times the reference clock (2). A calibration pulse generation circuit (5) for outputting a second calibration signal (CALin (2)) having a period larger than the period of the calibration signal (CALin (1)) to the time width expansion circuit (6);
A first count number (C (1)) obtained by counting a signal corresponding to the first calibration signal (CALin (1)) via the time width expansion circuit (6) according to the reference clock (2); A counter (9) for outputting a second count number (C (2)) obtained by counting a signal corresponding to the second calibration signal via the time width expansion circuit (6) according to the reference clock (2); Prepared,
The vibration pressure sensor, wherein the arithmetic circuit (10) calculates the physical quantity based on a difference between the second count number (C (2)) and the first count number (C (1)). Frequency measurement circuit. 2. The time width expansion circuit inputs a signal relating to a rise time difference between the synchronization signal and the frequency signal and a signal from the calibration pulse generation circuit by switching in a time division manner. Frequency measurement circuit. The calibration pulse generation circuit generates a first calibration signal at a time near the middle of the m-th cycle (m is an integer) and the (m + 1) -th cycle from the start of measurement, and the m + 1-th cycle and the (m + 2) -th cycle. The frequency measurement circuit according to claim 1, wherein the second calibration signal is generated at a time near the middle. 4. The calculation circuit according to claim 1, wherein the arithmetic circuit calculates an actual enlargement ratio from a count value applied to the first calibration signal and a count value applied to the second calibration signal. The frequency measurement circuit described in 1 .

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