JPS5849828B2 - 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 hundred MHz or more, and in particular, to a frequency measuring device for measuring high frequencies of, for example, several hundred MHz or more. The present invention relates to a frequency measurement device that measures an input signal frequency using an intermediate frequency signal generated by the input signal.

The frequency of an input signal can be measured by directly counting each cycle of the input signal for a unit of 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 input 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 input 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 Fx, respectively.
and Fi2, and the harmonic order is n (if n is l, 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, FA'1 by two measurements,
From FA2 and Fi t 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 0 or a number below the decimal point, for example α20
．． 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, F7 may be Fl1 or Fl2 measured previously, or a local oscillation frequency measured separately from these.

Similarly, Fi may be Fi1 or F12 or a separately measured intermediate signal frequency.

However, in any case, the local oscillation frequency and intermediate signal frequency are measured at the same time.

Generally, in order to obtain the harmonic order N, it can also be determined by the intermediate frequency and local oscillation frequency obtained in a short measurement time, and the measurement accuracy of the intermediate frequency signal frequency and local oscillation frequency to obtain the exact N. 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.

When sweeping the local oscillation frequency from high to low, FA?
2 becomes smaller, and since the input signal frequency Fx is constant, when Fx is high, Fi2 becomes higher than the measured intermediate frequency Fi1.

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

On the other hand, when the input signal frequency Fx is lower than the local oscillation frequency, the obtained intermediate frequency Fil is higher than Fi2, and therefore, in that case, equation (5) is made to take the difference.

That is, the magnitude relationship between the measured intermediate frequencies Fil and Ft2 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 frequency Fil P Fi2 and the local oscillation frequencies Fl1, Fl
2 is measured, and the arithmetic circuit calculates equations (3) and (4), and also determines the magnitude relationship between Fi1 and F12, and calculates the result, the harmonic order N obtained from equation (4), and the local The input signal frequency Fx is calculated from the oscillation frequency Fl 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.
71 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 a human input signal even if the frequency fluctuates.

According to the present invention, the measurement of the intermediate frequency and the measurement of the local oscillation frequency are performed simultaneously with time intervals at least three times.
The calculation of the above equation (3) is performed for a plurality of different combinations of two of the simultaneous measurements, and the harmonic order N is determined from the average of the plurality of calculation results.

Or the above (4) for a plurality of different combinations of the above two.
) Calculate each harmonic order N from the equation, and when the N matches are obtained, that N is determined to be the correct harmonic order.

Next, a description will be given 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 having a frequency Fx is supplied from an input terminal 11 to a frequency converter 12 .

The frequency converter 12 is supplied with a locally oscillated wave of frequency F7 from the 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 10MHz~
It has an amplification band of 400 MHz.

The frequency Fi of the intermediate frequency signal from the amplifier 16 is measured by the intermediate frequency measuring stage 17, and the local oscillation frequency F7 of the local oscillator 13 is measured by the local oscillation frequency measuring means 18.

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 means 17 and local oscillation frequency measuring means 18 simultaneously measure twice at intervals.

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 falling edge of the gate signal from the gate signal generation circuit 27, and the arithmetic circuit 29 takes in the contents of the counters 22 and 24, that is, each measured frequency, and after taking in the contents of the control circuit 25. The counters 22 and 24 are each reset by a reset signal from the output terminal 31.

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 intermediate frequency output from the frequency converter 12 decreases with time as shown in FIG. 2B. It becomes a signal.

Although the input signal frequency Fx is constant, the frequency NF/ 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 T1 as shown in FIG. The signal is supplied to the circuit 14 and its sweep 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.

Therefore, during the period T2, the intermediate frequency signal from the amplifier 16 is counted by the counter 22 and its frequency Fil is measured.
At the same time, the local oscillation signal passed through the gate 23 is counted by the local oscillation counter 24, and the oscillation frequency at that time is F7l! 1 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 t, a timing signal is again generated from control circuit 25 through terminal 26 as shown in FIG. 2E.

Therefore, the second gate signal is generated from the gate signal generation circuit 21 as shown in FIG. and is taken into this arithmetic circuit 29.

Local oscillation frequency F71,Fll measured in this way
2 and intermediate frequencies Ft1 p Ft2 are respectively taken into the arithmetic circuit 29, and based on these, the above (3)
The calculation of equation (4) is performed to determine the harmonic order N, and the magnitude relationship between the intermediate frequencies Fil and F i2 at this time is determined.

Thereafter, the arithmetic circuit 29 performs the calculation of equation (5) using N, the magnitude relationship, the intermediate frequency Fll (or Fi2), and the local oscillation frequency pzt (or Fl2).

In this case, in this example, Fi is large and the local oscillation frequency is swept high, so
In the conversion operation in the frequency converter 12, an intermediate frequency signal is obtained by subtracting N times F7 from the input signal frequency.

In other words, since the input 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.

The 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 generating circuit 27 generates a gate signal having an accurate time width T2 by counting accurate clocks, for example.

The intermediate frequency and local oscillation frequency are measured by the counters 22 and 24, respectively, and the measurement may be detected by the falling edge of the gate signal, but the timing signal shown in FIG. 2E can also be detected in the microcomputer. , the microcomputer itself can know when the counting of the counters 22 and 24 has finished, and therefore the microcomputer can start the counting of the counters 22 and 2 at an appropriate time.
Capture and store the contents of step 4.

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.

The point of measuring the frequency of the incoming signal at high speed is to measure the intermediate frequency Fi and local oscillation frequency F7 for formulas (3) and (4) for calculating the harmonic order N in a relatively short time. preferred.

However, in order to calculate the input 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 a gate signal for frequency measurement, that is, intermediate frequency measurement for calculating the input signal frequency and local oscillation frequency measurement, the terminal 31 of the microcomputer 35 is set to a low level, and the time base and other signals are transmitted through the inverter 39. 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 Fl is multiplied by N times, so if there is an error in this, it is multiplied 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 the voltage controlled oscillator 15 is phase-compared with the clock for determining the accuracy of the gate signal generation circuit 27, that is, the clock of the terminal 36, in the phase comparison circuit 43, and the phase difference output is supplied to the adder 41. and is 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 comparison circuit 43. and oscillator 1
The oscillation phase of the local oscillator 13 is synchronized with the oscillation phase of the gates 21 . It is synchronized with the gate signal that controls 23.

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

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 generating circuit 14, the output of the terminal 26 is applied 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 state at that time is maintained.

The frequency of the clock at terminal 36 is selected, for example, to be on the order of IMHz.

A clock for generating the gate signal of the gate signal generation circuit 2T 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 input signal frequency Fx changes, the change in the local oscillation frequency (F
l1 to Fl2), it becomes impossible to determine N correctly.

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

That is, simultaneous measurement of the intermediate frequency and local oscillation frequency is performed three or more times at time intervals.

Equation (3) is calculated for each of the two different sets of simultaneous measurement results to obtain the average value, and the harmonic order N is determined from the average value.

Or for each two different sets of the above simultaneous measurement results (4)
The calculations of each equation are performed, and if the calculation results N match, this is determined as the correct harmonic order; if they do not match, the measurement is repeated.

If the measurement time interval is varied, and the measurement interval is randomly varied, especially when measurements are to be made a large number of times, the input signal frequency will not change randomly, and more accurate measurements will be performed.

Furthermore, in this case, accurate measurements can be made even if the input signal frequency changes more than the sweep frequency range of the local oscillation frequency.

An example of this is shown in FIG. 4, in which parts corresponding to those in FIG. 1 are given the same reference numerals.

The characteristic feature in this case is the gate signal generation circuit 21, in which the gate signal is generated at random timing.

For this purpose, for example, a pseudorandom pulse generator 51 is provided.

That is, for example, a clock having a frequency of IMHz at the terminal 36 is set to 100 by the frequency dividing circuit 52 and is supplied to the pseudo random generator 51.

A match between the output of the pseudo-random pulse generator 51 and the clock at the terminal 36 is detected by the NAND gate 53.

The output of the pseudorandom pulse generator 51 is, for example, as shown in FIG. 5A.
As shown in FIG. 5B, the pulse width and pulse interval are generated as a random signal, and at each rising point, a negative pseudo-random timing signal is obtained as the output of the NAND gate 53 as shown in FIG. 5B.

In order to obtain a gate signal of a constant width at this timing, a flip-flop 54 is set by the output pulse of the NAND gate 53, and the output of the flip-flop 54 is supplied to a gate 55, and a gate 21, which is a router that counts the intermediate frequency and local oscillation frequency, respectively. 23.

A clock from the terminal 36 is supplied to the gate 55, and the output clock of the gate 55 is connected to the time base 38.
given to.

The output of time base 38 resets flip-flop 54.

In this way, as shown in FIG. 5C, the NAND gate 53
A gate signal with a constant width T2 is obtained every time an output pulse of 21 . 23 respectively.

In this way, the frequency is measured multiple times, but at the trailing edge of each gate signal, the microcomputer 35
monitors the gate signal, and when it falls, counter 2
2 and 24, that is, the measured intermediate frequency and local oscillation frequency are respectively taken in.

Thereafter, the gate signal is also supplied to the delay circuit 56, and a reset pulse delayed by a certain period of time after the gate signal is obtained as shown in FIG. 5D, and these reset pulse counters 22 and 24 are reset.

Take out sets of each measured intermediate frequency and local oscillation frequency for two different adjacent measurement points,
For multiple sets of Fi - 11', the calculations are performed in line Fl2, respectively.
F4 No, average each of those values and add α to it to get an integer N.

Alternatively, the calculation of equation (4) is performed for the plurality of sets, and if the resulting N matches, it is set as the correct harmonic order, and if they do not match, the three or more measurements are repeated.

In this way, the harmonic order N is determined, and furthermore, after or before determining the harmonic order, the terminal 5 of the microcomputer 35 is
A repulse from T is applied to the set terminal of the flip-flop 54 through the OR gate 58 to set it, and at the same time, the repulse from the terminal 3T is applied to the set terminal of the flip-flop 54.
is set to a low level, the output of the inverter 39 is set to a high level, and the time of the time base 38 is switched to make the time width of the gate signal sufficiently large.

The intermediate frequency and local oscillation frequency are measured using this sufficiently large gate signal, and the input signal frequency Fx is calculated from these and the harmonic order previously determined by averaging.

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

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 0 MHz 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.

Particularly, as mentioned above, when the harmonic order is determined by averaging, 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 partial modification of the frequency measuring device shown in Fig. 1. FIG. 4 is a block diagram showing an example of the frequency measuring device according to the present invention, FIG. 5 is a time chart for explaining its operation, and FIG. 6 is a partial modification of the device of the present invention. FIG. 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 sweeping local oscillator, which is supplied with an output and an input signal of the local oscillator, and whose frequency is the difference between the frequency of the input signal and the output frequency of the local oscillator and the frequency of its harmonics. A frequency converter that generates an intermediate frequency signal, an amplifier that amplifies the output of the frequency converter, an intermediate frequency measuring means that measures the output frequency of the amplifier, and a local oscillation frequency measurement that measures the output frequency of the local oscillator. means, a control means for causing the first half intermediate frequency measuring means and the local oscillation frequency measuring means to simultaneously measure three or more times at time intervals, and two different combinations of the three or more simultaneous measurements. Calculate FtI Ft2 from the two measured intermediate frequencies Fi1 and Fi2 and the two measured local oscillation frequencies Fl1 and Fl2, find the harmonic order N from the results of these multiple calculations Fl2-Fl1, and calculate the harmonic order N and the local oscillation frequency FA? and a calculation circuit that calculates the frequency of the human input signal from the corresponding intermediate frequency Fi.