JPS61223662A - Frequency measuring system - Google Patents

Abstract

PURPOSE:To attain a sufficiently small measurement error and a high resolution and to measure a signal frequency by generating a stable high frequency signal having the n-fold frequency for the signal to be measured and counting the high frequency signal with the time base of a prescribed time. CONSTITUTION:The output of a frequency divider 115 is so adjusted automatically that this output and the signal to be measured inputted to a phase comparator 111 have the same frequency and have phases synchronized with each other. Consequently, the high frequency signal having the n-fold frequency of the signal to be measured is outputted from the output terminal OUT of a DPLL 110 as the connection point between frequency dividers 114 and 115 phase- synchronously with input pulses. In a frequency measuring means, a counter 121 receives a time base signal of a time T from a time base generator and counts the number of pulses of the high frequency signal form the DPLL 110 on the time base T. This counted value is multiplied by 1/(nT) in a frequency discriminating circuit 122 to measure and output the frequency of input pulses.

Description

[Detailed Description of the Invention] [Summary] In the frequency measurement method, by multiplying and measuring the input signal, it is possible to measure five frequencies with high accuracy in a short time.

[Industrial application field]

The present invention relates to a method for measuring the frequency of a signal under test, and more particularly, to a frequency measurement method capable of measuring the frequency of a signal under test with a small measurement error and high resolving power in a limited short measurement reference time.

[Conventional technology]

When measuring the frequency of a signal under test, the frequency of the signal under test that is input within a fixed measurement reference time (time base) T is counted. In this case, as shown in FIG. 4, an error of one manpower occurs at time T.

FIG. 4 shows an example in which the signal to be measured is a pulse, and a counter (not shown) performs counting according to the falling edge of the input pulse. The counter asynchronously counts the number of input pulses using the rotation time T from time to to tl as a time base.

Therefore, depending on the phase relationship between the counting start time to and the input pulse, the number of input pulses counted at the time base T is 2 (in the case of (a)) or (P -1) (in case (b)), and a 1-bit frequency error occurs.

Therefore, the frequency of the input pulse to be measured is P
/T or (P-1>/T, resulting in a measurement error of (1/T)H2).

This measurement error is inversely proportional to T, so in order to reduce the measurement error and improve the measurement resolution, conventional methods
The base length T was increased.

[Problem that the invention seeks to solve]

In the conventional frequency measurement method, as described above, the measurement error is reduced by increasing the length T of the time base, and the resolution ability is improved.

However, in systems such as communication equipment, there are often restrictions on the time base when measuring the input signal frequency therein. In this case, if the length of the time base is short, the conventional frequency measurement method has a problem in that measurement errors become large and satisfactory resolution ability cannot be obtained. For example, set the time base length T to 200
If m5ec is used, a large measurement error of 5H2 will occur, so 1000H2, 1005H2, l0IOH2, etc.
When there are a plurality of input signals having a frequency difference of several H2, it is not possible to obtain sufficient resolution ability to reliably identify these signals.

The present invention was made in order to solve the above-mentioned problems in the conventional frequency measurement method.
It is an object of the present invention to provide a frequency measurement method that can measure the frequency of a signal to be measured with small measurement errors and high resolving power at the base.

[Means for solving problems]

Solving the aforementioned problems with conventional frequency measurement methods,
The means taken by the present invention to achieve the above object will be explained with reference to FIG.

FIG. 1 is a block diagram showing the configuration of the present invention. In FIG. 1, 110 is a harmonic generation means that generates a harmonic signal having a sufficiently stable frequency n times that of the signal under test. 120 is a frequency measuring means that counts the frequency of the harmonic signal output from the harmonic generation signal 110 on a time base of time T to measure the frequency of the signal under test.

[For production]

The operation of the present invention having the configuration shown in FIG. 1 will be explained with reference to the timing chart of FIG. 2. Figure 2 shows an example where the signal under test is a pulse signal, but the following explanation is common to measurement of various signal frequencies under test, such as pulse signals and sine wave signals. be.

The signal to be measured is multiplied by n times by the harmonic generation means 110 and applied to the frequency measurement means 120. The frequency of the harmonic signal added by means 110 is measured.

Since the measurement by the frequency measuring means 120 is performed asynchronously with the phase of the signal under test, the measurement start time t.

The count value changes depending on the phase relationship between the signal and the signal under test.

If the frequency measuring means 120 counts at the falling edge of the input signal, the counted value of the time base T of the signal under test shown in FIG. 2(a) will be P.

When the frequency of the harmonic signal obtained by doubling this signal under test is counted, the count value is (2P-2) (Figure 2 (in the case of bl) or (
2P-1) (in the case of FIG. 2(C)). In the case of a harmonic signal obtained by multiplying the signal under test by n, the count value is (n
P-1) or (nP-2).

The frequency measuring means 120 measures the frequency of the signal under test by multiplying this count value by (1/nT), and the measured signal frequency under test is CP/T (1/nT).
nT) or (P/T - (2/nT). Therefore,
Both measurement errors are greatly reduced to (1/n'r).

As described above, according to the present invention, measurement can be performed using the same time base as the conventional frequency measurement method, and the measurement error can be reduced to (1/n) compared to the conventional frequency measurement method. The decomposition ability can also be increased by n times.

〔Example〕

An embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 3 shows an embodiment of the present invention.

In FIG. 3, the harmonic generation means 110 and the frequency measurement means 120 are as described in FIG. 1.

In this example, the signal under test is a pulse signal,
As the harmonic generation means 110, a digital PLL (
DPLL (digital phase lock loop) is used. DPL constituting harmonic generation means 110
In L, 111 is a phase comparator, 112 is a sequential filter, 113 is a digital VCO (<voltage controlled oscillator), 114 is a frequency divider with a frequency division ratio (n/Q: n-Q is a positive integer), 115 is a frequency divider with a frequency division ratio of (1/n).

With this configuration, the input pulse (signal under measurement) input to the phase comparator 111 and the output of the frequency divider 115 are automatically adjusted to have equal frequencies and synchronized phases. Therefore, the connection point of frequency dividers 114 and 115, i.e., DPLL
From the output terminal OUT of (110), a harmonic signal whose frequency is multiplied by n times is output in phase synchronization with the input pulse.

Note that the configuration and operation of this DPLL (110) are well known, so detailed explanation thereof will be omitted. Since a PLL or a DPLL oscillates extremely stably, it is possible to generate a sufficiently stable n-multiplied high frequency signal.

In the frequency measuring means 120, 121 is a counter,
A time base generator (not shown) generates a time signal at time T.
DP at this time base T.
The number of pulses of the harmonic signal input from LL (110) is counted.

122 is a frequency identification circuit that measures the frequency of the input pulse by multiplying the count value of the counter 121 by (1/nT) and outputs the frequency. If the input pulse (signal under test)
F+ with a constant frequency.

F2. If the frequency is specified as F3, etc., it is determined from the measured value whether the frequency is Fl, F2, F3, etc., and the identification result is output.

Incidentally, when the multiplication number n of the signal under test is increased, the measurement error becomes smaller in inverse proportion to n and the resolution ability is improved, but on the other hand, the configurations of the counter 121 and the frequency identification circuit 122 become complicated. Therefore, considering the measurement error, resolution ability, difficulty in configuring each circuit element, cost, etc. necessary for measuring or identifying the signal under test, the multiplier n, that is, the frequency divider 115
The frequency division ratio of the frequency divider 114 (1/n), the frequency division ratio of the frequency divider 114 (n/Q
), the oscillation frequency of the digital VCO 113 is selected as appropriate.

With the above configuration, as explained in the [Operation] section above,
The frequency of the signal to be measured can be measured with a sufficiently low measurement error of (1/nT)H2.

Although one embodiment of the present invention has been described above, the present invention is not limited to this embodiment.

For example, when the signal under test is a sine wave, a normal PLL is used as the harmonic generation means 110 instead of a DPLL. As the harmonic generation means 110, DPLL or PL
In addition to L, various other stable multipliers can be used.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to measure the frequency of a signal under test with sufficiently small measurement error and high resolution in a limited and short measurement reference time (time base). .

[Brief explanation of drawings]

Fig. 1 is a detailed explanatory diagram of the present invention, Fig. 2 is a time chart for detailed explanation of the present invention, Fig. 3 is an explanatory diagram of an embodiment of the present invention, and Fig. 4 is a conventional frequency measurement method. A time chart explaining the operation of each is shown. In FIG. 1, 110: harmonic generation means, 120: frequency measurement means. Patent applicant Fujitsu Chiryu Co., Ltd. v\hy+
To the product u,, /71tuQ @Figure 1 ↑0 ↑1,000 shots Illη's ◆Ha 4th m, 4th 2nd ■

Claims (2)

[Claims] (1) In a frequency measurement method that measures the frequency of the signal under test by asynchronously counting the frequency of the signal under test that is input within a certain measurement reference time, (a) Harmonics obtained by multiplying the frequency of the signal under test (b) harmonic generation means (110) for generating a signal; (b) harmonic generation means (110) within a certain measurement reference time;
110) Frequency measurement means for counting the frequency of the output harmonic signal to measure the original signal frequency to be measured. (2) The frequency measurement method according to claim 1, wherein the harmonic generation means is a PLL or a digital PLL.