JPH0658963A - Method and apparatus for measuring frequency - Google Patents

Abstract

PURPOSE:To obtain a frequency measuring apparatus in which a PLL circuit itself can be taken into advantage by providing means for capturing an oscillator control signal in a PLL circuit, means for measuring the frequency of output signal from PLL based on the control signal, and means for estimating the frequency of input signal. CONSTITUTION:A phase comparator 1 compares the phases of input and output signals and delivers an error signal to a loop filter. The loop filter comprises a multiplier 2 and an integrator 3 and determines data for controlling a numeric control oscillator 4 based on the error signal from the comparator 1. The oscillator 4 can control the oscillation frequency based on the control data. An I/O unit 8 delivers control data from the oscillator 4 to a CPU 7. A ROM 5 stores a program and a RAM is a working memory for the CPU. An output unit 9 displays the results. The oscillator 4 oscillates at a frequency determined for the control data. This constitution determines an oscillation frequency through calculation based on a control data being input to the oscillator 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for measuring the frequency of electric signals.

[0002]

2. Description of the Related Art Generally, a PLL is used for the purpose of generating a signal having the same frequency and the same phase as an input signal.
Therefore, in order to know the frequencies of the input signal and the output signal of the PLL, it is necessary to connect a measurement circuit or a measurement device (frequency counter or the like) to the outside and measure.

[0003]

However, the above-mentioned conventional measuring method has the following problems. 1. In addition to the PLL circuit, it is necessary to add a circuit or device for frequency measurement, which complicates the device. 2. When the frequency of the input signal is high or wide, a complicated measurement circuit and a device with high measurement capability and a wide measurement range are required.

An object of the present invention is to provide a frequency measuring device using the PLL circuit itself, which can solve the above problems.

[0005]

In order to solve the above-mentioned problems, the present invention provides a means for acquiring a control signal (data) of an oscillator in a PLL circuit and a PLL output signal from the control signal (data). Means for measuring the frequency and means for estimating the frequency of the input signal based on the frequency are provided.

[0006]

According to the above construction, the frequency can be determined from the relationship between the detected control signal and the oscillation frequency, and
It is possible to estimate the frequency of the input signal from the output signal of the PLL by utilizing the property that the output signal of the PLL is synchronized with the input signal.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the configuration of an embodiment of the present invention. In FIG. 1, 1 to 4 are components of a digital PLL, and 5 to 9 are a microprocessor and its peripheral devices. The phase comparator 1 compares the phases of the input signal and the output signal and sends the resulting error signal to the loop filter. The loop filter is composed of a multiplier 2 and an integrator 3, and determines control data for controlling the numerically controlled oscillator 4 based on the error signal from the phase comparator 1. The numerically controlled oscillator 4 can control the oscillating frequency according to the control data.

The I / O device 8 sends the control data of the numerically controlled oscillator 4 to the CPU 7. The ROM 5 holds a program, and the RAM 6 is a working memory of the CPU. The output device 9 displays the result. The numerically controlled oscillator 4 oscillates at a frequency that is uniquely determined for the control data. Therefore, the oscillation frequency can be calculated from the control data input to the numerically controlled oscillator 4. In this embodiment, the I / O device 8 and the CPU 7 are used to obtain the control data and calculate the frequency. The control data is taken into the CPU 7 through the I / O device 8 and applied to the relational expression there to obtain the oscillation frequency. The relational expression between control data and oscillation frequency is built in the program in advance.

The instantaneous value of the output signal frequency of the PLL can be measured by the above procedure. Next, the operation of the frequency measuring method for the input signal of the PLL configured as described above will be described. In the PLL,
By comparing the phases of the input signal and the output signal and feeding back the error to the oscillator through a loop filter, the frequency and phase of the output signal are aligned with that of the input signal. Now, consider a case where an input signal whose frequency fluctuation can be ignored is added to a PLL circuit oscillating at an appropriate frequency. Immediately after adding the input signal, the error signal from the phase comparator 1 is large, and the control data of the numerically controlled oscillator 4 greatly fluctuates every time feedback is applied. But,
As the feedback is repeated, the error signal becomes smaller and the fluctuation of the control data also becomes smaller. Finally, the frequencies and phases of the input and output signals are almost the same. When this steady state is reached, the error signal becomes almost 0, and the control data of the numerically controlled oscillator 4 also becomes almost constant.

Therefore, the CPU 7 samples the control data of the numerically controlled oscillator 4 for an appropriate time, and when the variation of the sample reaches the steady state, it can be estimated that the frequencies of the input and output signals match. The control data at this time converted into the frequency by the above procedure may be considered as the input frequency. In this example, the variance was used as an index of whether or not the steady state was reached. When the variance of the sample becomes smaller than a fixed value defined by the program, the frequency converted from the average value is regarded as that of the input signal of the PLL.

The present invention is not limited to this embodiment. For example, a function of converting the control data of the numerically controlled oscillator 4 into a frequency is realized by a logic circuit, and a PLL is used.
It is also possible to integrate it with the circuit. The analog PLL shown in FIG. 2 becomes a simple frequency meter if the control voltage input to the voltage controlled oscillator 12 is added to the voltmeter and the frequency is scaled. Further, if a CPU is used in an analog PLL, the control voltage can be A / D converted and calculated using a relational expression of voltage and frequency.

[0012]

As described above, according to the present invention, the following effects can be obtained. 1. In the case of the device using the PLL circuit, the frequency of the input signal can be easily measured, and it is not necessary to add another frequency measuring circuit. Especially when equipped with a CPU,
Very easy to achieve. As a result, the scale and cost of the device can be reduced. 2. The frequency can be measured more easily than before regardless of the frequency of the input signal. 3. If a PLL-IC with a frequency measurement function is created, the number of parts can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a frequency measuring device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing the configuration of another embodiment of the main part of the present invention.

[Explanation of symbols]

 1 Phase Comparator 2 Multiplier 3 Integrator 4 Numerically Controlled Oscillator 5 ROM 6 RAM 7 CPU 8 I / O Device 9 Display Device 10 Phase Comparator 11 Loop Filter 12 Voltage Controlled Oscillator

Claims (5)

[Claims] 1. A means for acquiring a control signal for controlling an oscillator in a PLL circuit, and the PLL based on the control signal.
A frequency measuring device comprising: a measuring means for measuring the frequency of an output signal of the circuit; and an estimating means for estimating the frequency of the input signal based on the frequency. 2. The frequency measuring device according to claim 1, wherein the PLL circuit includes the oscillator, a phase comparator, and a loop filter. 3. The frequency measuring device according to claim 2, wherein the loop filter is composed of a multiplier and an integrator. 4. The measuring means and the estimating means include a CPU and a phase comparator in the PLL circuit, and based on the control signal when the control signal reaches a steady state by a feedback operation of the PLL circuit. The frequency measuring device according to claim 2, wherein the frequency of the input signal is estimated. 5. An input signal whose frequency fluctuation can be ignored is PL
When a control signal for controlling the oscillator in the PLL circuit is input to the L circuit and it is detected that the control signal has reached a substantially steady state by a loop in the PLL circuit, the control signal is set in advance. A frequency measuring method, characterized in that the frequency of the input signal is estimated by converting it into a frequency based on a defined relationship.