JPS5849827B2 - frequency measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency measuring device for measuring high frequencies of, for example, several 100 MHZ or more, and in particular, a frequency measuring device that mixes the frequencies of an input signal, a local oscillation signal, and its harmonics using a frequency converter. The present invention relates to a frequency measuring device that measures an input signal frequency using an intermediate frequency signal obtained from an output.

When measuring the frequency of a human input signal, it can be done by directly counting each cycle of the input signal for a unit time.

However, when the input signal frequency becomes higher than microwave, there is no counter that can directly count such a high frequency, or it becomes extremely expensive.

From this point of view, the input signal frequency is determined by converting the input signal into an intermediate frequency signal and measuring the frequency of the intermediate frequency signal.

Furthermore, in order to obtain an intermediate frequency signal over a wide frequency band, a frequency converter, a so-called harmonic mixer, is used to obtain not only the difference between the input signal frequency and the local oscillation signal frequency, but also the difference between harmonics of the local oscillation signal frequency. The human power signal frequency is measured from the wave number of the obtained intermediate frequency signal.

In this case, it is necessary to know whether the obtained intermediate frequency signal is frequency-mixed with the local oscillation signal itself or its harmonics, and the measurement operation for this is complicated and quick. It was not possible to make measurements.

From this point of view, for example, US Patent No. 3,932,814 (1
(Published on January 13, 1976) As shown in the specification, the human signal frequency is calculated from the time difference in which signals with the same intermediate frequency are obtained by changing the local oscillation frequency. This is the result of frequency mixing with the harmonics of the input signal, but some systems calculate the input signal frequency by knowing the order of the harmonics.

In this case, good linearity is required between the control signal that controls the frequency of the local oscillator and the output signal frequency of the local oscillator.

Moreover, it is necessary to vary the frequency of the local oscillator over a wide band, making it extremely expensive to construct such a local oscillator.

From this point of view, we proposed the following frequency measuring device.

That is, the oscillation output from the frequency sweep local oscillator and the input signal are supplied to the frequency converter, and an intermediate frequency signal of the difference between the input signal frequency and the output frequency of the local oscillator and its harmonic frequency is extracted.

This intermediate frequency signal is amplified by an amplifier. This amplifier amplifies a relatively wide frequency band.

The output frequency of this amplifier and the oscillation frequency of the local oscillator are measured by intermediate frequency measuring means and local oscillation frequency measuring means, respectively.

The measurements are taken simultaneously and twice at intervals.

These measurements are performed under the control of a control means.

The current input signal frequency is Fx, the local oscillation frequency in the first measurement is Fl1, the second measurement is Fl2, and the first and second measurement values of the intermediate frequency are Fi1, respectively.
and Ft2, and the harmonic order is n (if n is 1, it is the local oscillation frequency itself).

When the input signal frequency Fx is higher than the local oscillation frequency, the following relationship holds true.

From this equation (1), that is, Fl1, Fl by two measurements
2, Fi1, and Fi2, the harmonic order, that is, the harmonic order of the local oscillation wave from which the intermediate frequency signal was obtained is determined.

Therefore, the input frequency can be calculated from the obtained order n, the local oscillation frequency, and the intermediate frequency.

Generally, the local oscillation frequency or its harmonic frequency may be higher than the input signal frequency, so the local oscillation frequency and intermediate frequency obtained by two measurements have the following relationship.

The harmonic order n is calculated from such a relationship.

Equation (3) is not necessarily an integer because of measurement errors and because the input signal frequency may change.

Therefore, the correct harmonic order N can be determined by the following equation.

Here, α is O or a number below the decimal point, for example, α=0
．． 5, then N in equation (3) is rounded off.
is determined.

The input signal frequency Fx is determined by calculating the following equation from the integer value thus obtained, that is, the correct harmonic order N.

Here, Fl may be the previously measured Fl or Fl2, or a local oscillation frequency measured separately from these 1.

Similarly, Fi may be Fi1, Fi2, or a separately measured intermediate signal frequency.

However, in any case, the local oscillation frequency and the intermediate signal frequency are measured simultaneously.

In general, to find the harmonic order N, it can also be determined by the intermediate frequency and local oscillation frequency obtained in a short measurement time.In other words, the measurement accuracy of the intermediate frequency signal frequency and local oscillation frequency to find N is It may be relatively low.

However, in order to improve the accuracy of the calculation of equation (5), a highly accurate local oscillation frequency and intermediate frequency are required.

Therefore, it is preferable to measure the local oscillation frequency and intermediate frequency signal frequency separately from the measurement for determining N.

Now, when sweeping the local oscillation frequency from high to low, Fl2 will be smaller than the measured Fl1, and since the input signal frequency Fx is constant, if Fx is high, the measured intermediate Frequency F than Fll
i2 is higher.

Therefore, in such a state, equation (5) takes the sum.

On the other hand, when the human power signal frequency Fx is lower than the local oscillation frequency, the obtained intermediate frequency F i1 is Ft2
Therefore, in that case, equation (5) takes the difference.

That is, the magnitude relationship between the measured intermediate frequencies Fi1 and Fi2 is determined to determine whether to take the positive or negative value of equation (5).

Because of the above relationship, as mentioned earlier, the intermediate frequencies F i1 , F i2 and the local oscillation frequencies FA, , F
12 is measured, and the arithmetic circuit calculates equations (3) and (4), and also determines the magnitude relationship between Fi1 and Ft2, and calculates the result, the harmonic order N obtained from equation (4), and the local oscillation. The input signal frequency Fx is calculated from the frequency FA and the corresponding intermediate frequency Fi based on equation (5).

With the above method, the linearity of the oscillation frequency with respect to the control signal of the local oscillator does not need to be good, and the sweep frequency range may also be relatively narrow.

However, when the input signal frequency fluctuates, for example when the input signal is a frequency modulation signal, the fluctuation in the input signal frequency is the first measured local oscillation frequency F.
If the difference is greater than the difference between l1 and the second measured frequency Fl2, the harmonic order N cannot be determined.

An object of the present invention is to provide a frequency measuring device that can accurately measure the frequency of an input signal even if the frequency fluctuates.

According to this invention, the frequency sweep direction of the local oscillator is configured to be reversed, and the intermediate frequency and the local oscillation frequency are each measured twice by sweeping in one direction, and then the sweep direction of the local oscillator is reversed. Similarly, the intermediate frequency and local oscillation frequency are measured twice.

The above equation (3) is calculated for each of the two measurement results, the average is taken, and the harmonic order N is determined from the average value.

Alternatively, calculate N using the equation (4) for each of the two measurement results, and if the calculation results match, use it as the correct harmonic order, and if they do not match, repeat the same measurement until they match.

Next, let's explain with reference to the drawings.

First, frequency measurement by harmonic order determination using equation (4) proposed earlier will be described with reference to FIG.

An input signal of frequency Fx is supplied from a human power terminal 11 to a frequency converter 12 .

The frequency converter 12 is supplied with a locally oscillated wave of frequency Fl from a frequency sweep local oscillator 13.

The frequency sweep local oscillator 13 includes a sweep voltage generator 14 that generates a sweep voltage such as a sawtooth voltage, and a voltage controlled oscillator 1 whose frequency is controlled by the output sweep voltage.
It consists of 5 and more.

The frequency converter 12 outputs an intermediate frequency signal having a frequency that is the difference between the input signal frequency, the local oscillation frequency, and the frequency of its harmonics, and this is amplified by the amplifier 16.

The amplifier 13 has a relatively wide amplification band, for example 10MH2~
It has an amplification band of 400MH2.

The frequency Fi of the intermediate frequency signal from the amplifier 16 is determined by the intermediate frequency measurement stage 17 and the local oscillation frequency FA? of the local oscillator 13. are measured by the local oscillation frequency measuring means 18, respectively.

The intermediate frequency measurement stage 17 includes, for example, an intermediate frequency gate 21 to which the output of the amplifier 16 is supplied, and a counter 22 that counts the output of the gate 21.

The local oscillation frequency measuring means 18 includes a local oscillation wave gate 23 to which the output of the local oscillator 13 is supplied, and a local oscillation wave power counter 24 that counts the output of the gate 23.

These intermediate frequency measuring stages 17 and local oscillation frequency measuring means 18 are simultaneously measured twice at intervals of time.

A control means for this purpose is provided, and as the control means, for example, a control circuit 25 is provided, and a terminal 2 of the control circuit 25 is provided.
6 outputs a timing signal that determines the measurement timing, this timing signal drives the gate signal generation circuit 27, which generates a gate signal of a constant width, and this gate signal controls the opening and closing of the gates 21 and 23. .

A part of the output of the amplifier 16 is branched and supplied to a detector 28 , and when the detector 28 detects that an intermediate frequency signal is obtained from the amplifier 16 , it is supplied to the control circuit 25 .

As a result, the control circuit 25 transfers the timing signal to the terminal 2.
6.

The arithmetic circuit 29 is activated by the fall of the gate signal from the gate signal generating circuit 27, and the arithmetic circuit 29 starts the counter 2.
Incorporate the contents of 2 and 24, that is, each measured frequency,
Also, after the input, the output terminal 3 of the control circuit 25
The counters 22 and 24 are each reset by a reset signal from 1.

When the start switch of the frequency measuring device is turned on, terminal 33
When a start signal is applied to the sweep voltage generation circuit 14, the oscillation frequency Fl increases linearly from the local signal generator 13, for example, as shown in FIG. 2A.

The input signal from the input terminal 11 is frequency-mixed with the output of the local oscillator and its harmonics in the frequency converter 12, and the frequency Fi of the output intermediate frequency of the frequency converter 12 decreases with time as shown in FIG. It becomes a signal.

Although the input signal frequency Fx is constant, the frequency NFA of the harmonic of the local oscillation wave frequency-mixed with it gradually increases, so Fi decreases with time.

When this decrease enters the amplification band of amplifier 16, it is detected by detector 28 and its output is at time t, as shown in FIG. 2C.

Higher level. This detection signal is supplied to the control circuit 25, which generates a timing signal with a width T as shown in FIG. The signal is supplied to the generating circuit 14 and its sweeping operation is stopped.

In the gate signal generation circuit 27, as shown in FIG. 2F, a gate signal having a time width T2 smaller than T1 is generated at time t.

This gate signal causes gates 21 and 23 to be opened, respectively.

Therefore, during the period T2, the intermediate frequency signal from the amplifier 16 is counted by the counter 22, and its frequency Fi1 is measured.
At the same time, the local oscillation signal passing through the gate 23 is counted by a counter 24, and the oscillation frequency Fl at that time is measured.

These measured values are taken into the arithmetic circuit 29 and stored, for example, at the falling edge of the gate signal.

Thereafter, the period T1 of the timing signal applied to the terminal 26 of the control circuit 25 ends, and the local oscillator 13 starts frequency sweeping from this point on, so that the oscillation frequency increases again as shown in FIG. The intermediate frequency of the signal decreases.

Thereafter, a reset signal is generated at the terminal 31 of the control circuit 25 as shown in FIG.
is reset.

After a further lapse of a suitable period of time, at time t1, the timing signal is again generated from the control circuit 25 through the terminal 26 as shown in FIG. 2E.

Therefore, the second gate signal is generated from the gate signal generation circuit 27 as shown in FIG. The signal is taken into the lever arithmetic circuit 29.

Local oscillation frequencies F71 and Fl2 measured in this way
and intermediate frequencies F tl and I F t 2 are respectively taken into the arithmetic circuit 29, and based on these, the above (
The calculations of equations 3) and (4) are performed to determine the harmonic order N, and the magnitude relationship between the intermediate frequencies Fi1 and Ft2 at this time is determined.

Thereafter, the arithmetic circuit 29 calculates the equation (5) using these N, the magnitude relationship, the intermediate frequency Fi1 (or F12), and the local oscillation frequency FA1 (or Fl2).

In this case, in this example, Fi1 is large and the local oscillation frequency is sweeping to become high, so in the conversion operation in the frequency converter 12, N times Fl is subtracted from the input signal frequency, and the intermediate This means that a frequency signal is obtained.

In other words, since the human power signal frequency Fx is higher than the harmonic frequency of the local oscillation wave that acted on the frequency conversion,
The input frequency Fx in equation (5) is calculated by addition.

The calculation result is displayed on the display 34. Arithmetic circuit 29
and the control circuit 25 can be easily constructed as a single unit using a so-called microcomputer.

In that case, the detector 28 is controlled by the microcomputer.
The output of the oscillator 13 is periodically monitored, and when the output is obtained from the wave detector 28, the timing pulse shown in FIG. At the same time, the gate signal generation circuit 27 generates a gate signal having an accurate time width T2 by, for example, counting accurate clocks.

The intermediate frequency and local oscillation frequency are measured by the counters 22 and 24, respectively, and the measurement may be detected at the falling edge of the gate signal, but the timing signal shown in FIG. 2E can also be detected within the microcomputer. , the microcomputer itself can know when the counting of the counters 22, 24 has finished, and therefore the microcomputer can start the counting of the counters 22, 24 at an appropriate time.
Capture and store the contents.

In this way, each frequency is measured twice at intervals, and the measurement results are expressed using equations (4) and (5).
) can easily be performed under program control.

From the point of view of measuring the frequency of the input signal at high speed, it is important to measure the intermediate frequency Fi and local oscillation frequency Fl for formulas (3) and (4) for calculating the harmonic order N in a relatively short time. preferable.

However, in order to calculate the human power signal frequency Fx using equation (5) with high precision, it is desirable to measure the intermediate frequency and local oscillation frequency used at that time with high precision.

From this point, in addition to measuring the frequency for calculating the harmonic order N, a gate signal of relatively long time is applied to the gates 21 and 2.
3 to measure the local oscillation frequency and intermediate frequency.

For this reason, for example, in FIG. 3, parts corresponding to those in FIG. A semiconductor integrated circuit can be used.

This counts clocks and, depending on which of a plurality of terminals is selected, generates a pulse with a time width corresponding to the selected terminal.

Therefore, when generating a gate signal to determine the order N, for example, the terminal 3 of the microcomputer 35
7 is set to a high level and is applied to one terminal of the time base 38 to generate a gate signal pulse having a time width T2 in FIG.

However, when generating gate signals for frequency measurement, that is, intermediate frequency measurement for calculating the input signal frequency and local oscillation frequency measurement, the terminal 37 of the microcomputer 35 is set to a low level, and the time base is A signal is applied to a predetermined terminal of , thereby generating a gate signal having a desired time width, that is, a time width wider than T2.

In order for this time base 38 to operate only when necessary, a signal from the terminal 26 of the microcomputer 35 is applied to the reset terminal of the time base 38, so that it operates only while the signal at the terminal 26 is at a high level. In other cases, it is placed in the reset state.

When calculating the input signal frequency Fx, the local oscillation frequency FA'
is multiplied by N times, so if there is an error in this, it will be magnified by N times.

From this point of view, it is preferable not to allow even one bit of error.

For this purpose, for example, within the local oscillator 13, the output of the sweep voltage generator 14 is supplied to the adder circuit 41.
1 output is passed through the low frequency wave generator 42 to the voltage controlled oscillator 15.
is given as a control voltage.

On the other hand, the output of this voltage controlled oscillator 15 is the clock for determining the accuracy of the gate signal generation circuit 27, that is, the terminal 3.
The phase comparison circuit 43 compares the phase with the clock of 6 and the phase comparison circuit 43, and the phase difference output is supplied to the adder 41 and added to the sweep voltage of the sweep voltage generation circuit 14.

In this way, the feedback control loop from the phase comparator 43 for the voltage controlled oscillator 15 will deviate from its phase control range if the voltage from the sweep voltage generating circuit 14 is larger than a certain degree, and the voltage controlled oscillator 15 will eventually be forced to move out of the voltage controlled oscillator 15 by the sweep voltage. 1
5 frequencies are controlled.

However, when the change in the sweep voltage of the sweep voltage generation circuit 14 is less than a predetermined value or when the sweep of the sweep voltage is stopped, the frequency of the voltage controlled oscillator 15 is controlled by the output of the phase comparator circuit 43, and therefore the clock of the terminal 36 is and the oscillation phase of the oscillator 15 are phase synchronized, that is, the local oscillator 13
The oscillation phase of is synchronized with the gate signal controlling the gates 21 and 23.

Therefore, the counter 24 that measures the local oscillation frequency can accurately measure the local oscillation frequency without any counting error.

In FIG. 3, a counter is used as the sweep voltage generating circuit 14, and the clock from the terminal 36 is supplied to the counter 45 through the inhibit gate 44, and the count value of the counter 45 is converted into an analog signal by the DA converter 46. This is a case where a sawtooth wave sweep voltage is obtained from this DA converter 46.

In order to stop the voltage sweep to the sweep voltage generation circuit 14, the output of the terminal 26 is given to the inhibit gate 44, and while the signal of the terminal 26 is at a high level, the clock of the terminal 36 is not supplied to the counter 45, and the counter 45 is The counting status at that time is maintained.

The frequency of the clock at the terminal 36 is selected to be approximately IMHZ, for example.

A clock for generating a gate signal for the gate signal generation circuit 27 and a counter 4 in the sweep voltage generation circuit 14
A clock other than the clock supplied to 5 may be used.

The sweep voltage generation circuit 14 may not only use a counter as described above, but may also generate a voltage by integrating a constant DC voltage, and various other types of sweep voltage generation circuits may be used.

The harmonic order N can be determined by simultaneously measuring the intermediate frequency and the local oscillation frequency twice as described above.

However, when the human input signal frequency Fx changes, the change in the local oscillation frequency (F
71 to Fl2), it becomes impossible to determine N correctly.

In order to solve this problem, the present invention does the following.

In order to obtain the harmonic order N, the intermediate frequency and local oscillation frequency are simultaneously measured twice at a certain interval, and then the frequency sweep direction of the local oscillator 13 is reversed and the intermediate frequency and local oscillation frequency are simultaneously measured again. The measurement is carried out twice at a certain interval, and n is calculated using equation (3) using the results of both measurements.

Take the average of the two obtained n and use it to calculate (4
) from the equation or calculate the harmonic order N from the above two n
If the two Ns determined by equation (4) do not match, the measurement is repeated again.

To reverse the direction of the sweep force, for example, as shown in FIG.
Using an up-down counter, when the terminal 47 is at a low level, the counter 45 is placed in an up-counting state, and when it is at a high level, the counter 45 is placed in a down-counting state.

For example, as shown in FIG. 2G, at time t.

In the frequency measurement at t1, the local oscillation frequency is controlled to increase over time as described above, and the terminal 47 is set at a low level.

However, at this point t.

Terminal 47 is set to high level at time L2 after measuring the intermediate frequency and local oscillation frequency twice each at t1 and t1.

As a result, the up/down counter 45 becomes a down counter state, and subtracts from the current count every clock.

Furthermore, the microcomputer 35 generates timing signals at the terminal 26 at times t3 and t4, as shown in FIG. 2E, and at these timings, a gate signal is generated as shown in FIG. The intermediate frequency and local oscillation frequency are each measured simultaneously.

The harmonic order is calculated using this measurement result.

In calculating the harmonic order based on the measurement results by increasing the oscillation sweep frequency, calculate Fi1-Fi2, and similarly calculate FV2-FV.For the results measured at time points 3 and t4 by decreasing the local oscillation frequency, calculate FV2-FV. Also performs calculations based on this formula, and averages the results of both calculations, including their polarities.

As shown in equation (4), +α is added to the average value to determine an integer value, and N is obtained.

According to this determination of N, if the change in the input signal frequency is in a constant direction, the direction of change in the local oscillation frequency in the second calculation of n will be the same as the previous one, compared to the error included in the first calculation of n. Since this is the opposite of the case for the error, the error included in this calculation has the opposite polarity to the previous one, and the error will decrease if these two n calculations are averaged.

In order to invert the direction of the sweep force of this local oscillation frequency, it is possible not only to reverse the counting direction of the clock in the sweep voltage generation circuit 14, but also to generate a sweep voltage using an integral method and to control the input DC. The sweep direction can also be reversed by switching the voltage polarity.

In the above description, the local oscillation frequency was measured by directly counting the local oscillation waves with the counter 24, but the frequency can also be measured using a signal obtained from the sweep voltage generation circuit 14, for example.

For example, as shown in the main part of FIG. When the measured intermediate frequency is fetched, the contents of the coefficient multiplier 59 may be fetched at the same time.

The intermediate frequency may be measured using a regular period measuring device to measure the period and convert it into a frequency.

In the above, the sweep of the local oscillator was stopped each time the intermediate frequency or local oscillation frequency was measured to determine the harmonic order, but without such a stop,
Therefore, the frequency may be measured while the frequency is changing.

However, it goes without saying that the intermediate frequency within the measurement time T2 is limited to a range that does not deviate from the amplification band of the intermediate frequency amplifier 16, and furthermore, in this state, the oscillation frequency changes linearly with respect to the control voltage of the local oscillator. , the measurement frequency is the average frequency at measurement time T2,
The frequency at the midpoint of T2 is measured.

Even if the local oscillation frequency changes nonlinearly with respect to the control voltage, if the time T2 is small and the frequency change or the nonlinearity is sufficiently small, measurement can be similarly performed without stopping the frequency sweep.

As described above, in the frequency measuring device according to the present invention, when determining the harmonic order, it is relatively easy to determine the harmonic order.
A variation range of about H2 is sufficient, so an expensive one is not required.

Since the frequency change range may be small in this way, good linearity of the oscillation frequency with respect to the control voltage can be obtained, and highly accurate measurement is possible.

In particular, when the harmonic order is determined by averaging as described above, it is possible to measure even if the input signal frequency fluctuates.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of the proposed frequency measuring device, FIG. 2 is a time chart for explaining its operation, and FIG. 3 is a block diagram showing an example of the frequency measuring device according to the present invention. FIG. 4 is a block diagram showing a partial modification thereof. 11...Input terminal, 12...Frequency converter, 13...Local oscillator, 16...
Amplifier, 17...Intermediate frequency measuring means, 18.
...Local oscillation frequency measuring means, 25...
Control circuit, 29... Arithmetic circuit.

Claims (1)

[Claims] 1. A frequency sweep local oscillator that can change the oscillation frequency in either an increasing direction or a decreasing direction;
a frequency converter to which the output of the local oscillator and the human input signal are supplied, and which generates an intermediate frequency signal having a frequency that is the difference between the frequency of the input signal and the output frequency of the local oscillator and the frequency of its harmonics; an amplifier for amplifying the output of the converter, intermediate frequency measuring means for measuring the output frequency of the amplifier, local oscillation frequency measuring means for measuring the output frequency of the local oscillator, and sweeping of the local oscillator in one direction. The intermediate frequency measuring means and the local oscillation frequency measuring means are made to perform measurements twice at the same time with a time interval between each other, and then the direction of the sweeping force of the local oscillator is reversed and the intermediate frequency measuring means and the local oscillation frequency measuring means are measured again. A control means for causing the local oscillation frequency measuring means to measure twice at the same time with a time interval, and measuring frequencies F't1 and F twice by the intermediate frequency measuring means during the unidirectional sweep.
From t2y and the frequencies Fl, Fl2 measured twice by the local oscillation frequency measuring means, perform the following calculation, perform the same calculation for the measurement result after reversing the sweep direction, and calculate the high frequency order N from both calculations. , N, a local oscillation frequency F7, and an intermediate frequency Fi corresponding thereto, and a computing unit for computing the frequency of the input signal.