JPH04285864A - Frequency measuring apparatus - Google Patents

Abstract

PURPOSE:To obtain the title apparatus wherein a high-precision frequency mea surement may be attained with a low-precision frequency measuring device. CONSTITUTION:A frequency measuring apparatus is constituted of an oscillator 1 to be measured, a reference oscillator 2 oscillating frequency as near as possible to the oscillation frequency of the oscillator 1 to be measured, a mixer 3 multiplying the output of the oscillator 1 to be measured by the output of the reference oscillator 2, an LPF 4 taking out only the low frequency component of the output of the mixer 3 and a frequency measuring device 6 measuring the output frequency of the LPF 4. A schmitt trigger buffer 5 may be inserted on the output side of the LPF 4.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a frequency measuring device.
In particular, the present invention relates to a frequency measuring device that is capable of measuring high frequencies with high accuracy using a low-accuracy frequency measuring device for low frequencies.

0002

[Prior Art] In a conventional frequency measuring device, for example, as shown in FIG.
As shown in FIG. 1, there is a frequency measuring device 11 configured to directly measure the oscillation frequency of the oscillator 1 under test. Also, as shown in FIG. 3, the frequency divider 13 is connected to the frequency measuring device 1
There is also a device that is inserted before the oscillator 2 and divides the frequency of the oscillator under test 1 to make it a lower frequency for measurement.

0003

[Problems to be Solved by the Invention] In the frequency measuring device shown in FIG. 2 described above, the frequency measuring device 11 is required to have high accuracy higher than the frequency measurement accuracy (usually 10 times or more the measurement accuracy), and A frequency measurement range in which the oscillation frequency of the measurement oscillator 1 or higher can be measured is required. In particular, when measuring the oscillation frequency with high precision, there is a problem in that a frequency measuring device with higher precision than the measurement precision is required. This is the same in the case of the frequency measuring device 12 that measures frequencies using the frequency divider 13 in FIG. 3, although the high frequency measurement range is relaxed, but high accuracy is required. SUMMARY OF THE INVENTION An object of the present invention is to provide a frequency measuring device that can measure frequencies with high precision using a low-precision frequency measuring device.

0004

SUMMARY OF THE INVENTION The frequency measuring device of the present invention comprises: an oscillator to be measured whose frequency is to be measured; a reference oscillator that oscillates at a frequency as close as possible to the oscillation frequency of the oscillator to be measured; Consists of a mixer that multiplies the outputs of the measurement oscillator and reference oscillator, a low-pass filter that extracts only the low-frequency components of this mixer output, and a frequency measuring device that measures the output frequency of this low-pass filter. . If necessary, a Schmitt trigger buffer can be inserted at the output side of the low-pass filter.

[0005]

[Operation] According to the present invention, since the difference between the oscillation frequency of the oscillator under test and the oscillation frequency of the reference oscillator is measured with a frequency measuring instrument, measurement can be performed using a frequency measuring instrument with low frequency and low accuracy. .

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the present invention. In the figure, 1 is a VCXO (crystal oscillation type voltage controlled oscillator)
A reference oscillator 2 having an oscillation frequency as close as possible to the oscillation frequency of the oscillator 1 to be measured and having high frequency accuracy is provided to the oscillator 1 to be measured, and the outputs of these oscillators 1 and 2 are input to a mixer 3. In this mixer 3, each oscillator 1, 2
By multiplying the outputs of , the sum and difference of the frequency components of each output are output. Furthermore, the output of this mixer 3 is passed through an LPF (low pass filter) 4 to attenuate the sum component and extract only the difference component, and this difference component is passed through a Schmitt trigger buffer 5 and then filtered. The frequency is measured by the frequency measuring device 6. This Schmitt trigger buffer 5 has a function of removing harmonic components in order to prevent the frequency measuring device 6 from making erroneous measurements due to harmonic components contained in the output of the LPF 4.

Therefore, in this frequency measuring device, the frequency difference between the oscillator 1 under test and the reference oscillator 2 is measured in the frequency measuring device 6, and the oscillation frequency of the oscillator 2 is used to determine the oscillator 1 under test. The oscillation frequency of can be calculated. And when making this measurement,
The frequency measuring device 6 may be a low frequency measuring device capable of measuring frequency differences, and can measure with an accuracy comparable to that of the reference oscillator 2.

[0008] Specifically, using numerical values, the oscillation frequency of the reference oscillator 2 is 100 MHz, and the accuracy is 10-9.
(0.1Hz) Oscillation frequency of oscillator under test 1 100MHz ±1
0KHZ (100MHZ ± 100ppm) Difference between the above two frequencies ±10KHZ
±10 when the accuracy of the frequency measuring device 6 is 10 ppm
Error when measuring KHZ ± 0.1HZ (±10KHZ × 10ppm) Error (±
Therefore, using a measuring device with an accuracy of 10 ppm, it is possible to measure the frequency with an accuracy comparable to that of the reference oscillator (10-9 order). Note that the Schmitt trigger buffer may be omitted if there is no risk of the frequency measuring device 6 malfunctioning.

[0009]

Effects of the Invention As explained above, the present invention uses a low-precision frequency measuring device for low frequencies to measure the difference between the oscillation frequencies of the oscillator under test and the reference oscillator. This has the effect of being able to measure the oscillation frequency of the oscillator under test with average accuracy.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a block diagram of an example of a conventional frequency measurement device.

FIG. 3 is a block diagram of another example of a conventional frequency measurement device.

[Explanation of symbols]

1 Oscillator under test 2 Reference oscillator 3 Mixer 4 LPF 5 Schmitt trigger buffer 6 Frequency measuring device

Claims (2)

[Claims] [Claim 1] An oscillator under test whose frequency is measured;
A reference oscillator that oscillates at a frequency as close as possible to the oscillation frequency of the oscillator under test, a mixer that multiplies the outputs of the oscillator under test and the reference oscillator, and a low-pass filter that extracts only the low frequency components of the mixer output. 1. A frequency measuring device comprising: a low-pass filter; and a frequency measuring device that measures the output frequency of the low-pass filter. 2. The frequency measuring device according to claim 1, further comprising a Schmitt trigger buffer inserted on the output side of the low-pass filter.