JPH04248471A - Frequency measuring device - Google Patents

Abstract

PURPOSE:To enable frequency to be measured even in a wide frequency range by providing an equalizer with certain frequency characteristics at a previous stage of a phase discrimination circuit and a detection circuit of a video amplitude data which is determined by frequency characteristics at a later stage and determing frequency from the data and I/Q video quantized output. CONSTITUTION:An RF signal passed through an equalizer 10 with certain frequency characteristics and is fed to an I/Q phase discrimination circuit 5. An output QA of an adder 11 can detect a video amplitude which is determined by frequency characteristics of the equalizer 10. The video amplitude signal is converted to a quantized amplitude data, thus enabling ranges A and B of frequency measurement to be determined. A polarity is judged by a frequency calculation circuit 13 according to this amplitude data and an I/Q video, is code-converted, and is outputted as a digital data, thus enabling an uncertainty of a frequency precise measurement system of the I/Q video system to be compensated for by a rough measurement system of the amplitude data system and obtaining a high resolution.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency measuring device for measuring the carrier frequency of a pulse-modulated input RF signal.

0002

2. Description of the Related Art FIG. 5 is a simplified block diagram of a conventional frequency measuring device disclosed in, for example, Japanese Patent Laid-Open No. 1-152375. In the figure, 1 is an RF signal input terminal, 2
is a bandpass filter, 3 is a distributor that distributes the RF signal, 4 is a delay line, and 5 is an I/Q that detects the phase difference of input signals.
A phase discrimination circuit, 6 a zero cross slicer for quantizing I/Q video, 7 a frequency calculation circuit, and 8 an output terminal. Further, the configuration of the phase discrimination circuit 5 is as follows: 5a is a distributor, 5b is a 9
0° hybrid, 5c is a detector, and 5d is a differential amplifier. FIG. 7 is an output video waveform diagram of the I/Q phase discrimination circuit.

Next, the operation will be explained. The RF signal input to the RF signal terminal 1 is distributed by the signal distributor 3, and one is input as is to the I/Q phase discrimination circuit 5,
The other signal is input to the I/Q phase discrimination circuit 5 via a delay line 4 having a delay time τ. Each input R
The F signal is phase-combined by a distributor 5a and a 90° hybrid 5b, and then detected by a detector 5c.

0004

[Math 1]

[Math 2] However, K = constant θ=2πfτ (f is input RF frequency) As is well known,

Furthermore, the above outputs V1, V2, V3,
V4 is differentially amplified by the differential amplifier 5d, and as shown in FIG.
The I/Q video signal shown in is output and its period is 1.
/τ. The polarity of this I/Q video is quantized by a zero cross slicer 6 using OV as a reference, and a frequency calculation circuit 7
If you reverse the polarity with and then convert the output bit,
The input frequency can be calculated with an accuracy of 1/4 of one period (1/τ) of the reciprocal of the delay time. In this case, I
/Q video has the same output repeatedly at 1/τ, has multiple values with respect to frequency, and has uncertainty. Therefore, the input of the I/Q phase discriminator circuit 5 does not necessarily include a bandpass filter 2 that determines the measurement band. It becomes necessary.

[0006]

[Problems to be Solved by the Invention] Conventional frequency measurement devices are configured as described above, so as the frequency measurement band becomes wider, the resolution deteriorates. Therefore, in order to maintain measurement accuracy, phase discrimination with different delay times is required. There were problems in that the circuit had to be configured in multiple stages to subdivide the frequency division band and increase the resolution, making the device large and complex.

The present invention was made to solve the above-mentioned problems, and provides a stable device with a simple circuit configuration that can measure frequencies with high accuracy even when the frequency band to be measured becomes wider. The purpose is to

[0008]

[Means for Solving the Problems] A frequency measuring device according to the present invention includes an equalizer having a certain frequency characteristic at a stage upstream of a phase discrimination circuit that outputs an I/Q video, and an equalizer having a fixed frequency characteristic at a stage to the right of the phase discrimination circuit. This device includes a video amplitude data detection circuit determined by the frequency characteristics of the equalizer, and a frequency calculation circuit that calculates an input frequency from the video amplitude data and I/Q video quantization output.

[0009]

[Operation] The frequency measuring device of the present invention includes an equalizer having a constant frequency characteristic at the front stage of the phase discrimination circuit, and a detection circuit for video amplitude data determined by the frequency characteristic of the equalizer at the right stage of the phase discrimination circuit. Since the frequency is calculated from both the video amplitude data and the I/Q video quantization output, a wide frequency band can be measured.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a frequency measuring device that is an embodiment of the present invention, in which 9 is a limiting amplifier, 10 is a
11 is an equalizer with constant frequency characteristics; 11 is an adder; 12 is an A/D converter that quantizes the video signal; 13
is a frequency calculation circuit, and QA is a video amplitude signal. Other symbols are the same as those in the conventional circuit.

FIG. 2 is an explanatory diagram of the operation of one embodiment of the present invention, where A(1/τ) is 1 determined from video amplitude data.
The frequency measurement range of the period, B (1/τ) is the frequency measurement range of the next one period, and (1)-(8) on the 0 level line are the frequency division bands that divide A and B into 8 equal parts, a, b ,c,d,
e is frequency characteristic amplitude data of the equalizer corresponding to the frequency division band.

Next, the operation will be explained. The RF signal input to the RF signal input terminal 1 is inputted to the I/Q phase discrimination circuit 5 via the equalizer 10 having a constant frequency characteristic after the output level is made constant by the limiting amplifier 9. . The input RF signals are phase-combined and detected, and the I/Q video output is the same as in the conventional operation.

If the frequency characteristic of the equalizer 10 is set such that the loss characteristic is linear with respect to the input frequency as shown in FIG. 2, the amplitude of the I/Q video changes in accordance with the frequency characteristic of the equalizer 10. Furthermore, the output QA of the adder 11 that adds V3 and V4 is determined by the frequency characteristics of the equalizer 10, since it is not affected by the input frequency and has a constant video amplitude, as is clear from equation 2 above. It will be possible to detect the video amplitude.

This video shows how the amplitude signal is converted to the A/D converter 12.
The frequency measurement ranges A and B shown in FIG. 2 are determined by quantizing and converting into amplitude data.

This amplitude data and the zero cross slicer 6
After determining the polarity of the I/Q video quantized by the frequency calculation circuit 13, the code is converted and outputted to the output terminal 8 as digital data.

Next, from FIG. 2, the frequency determination method is based on the originally I
/Q video has a resolution of 1/4 of one cycle of the reciprocal of the delay time, 1/τ, so one cycle is divided into four equal parts, and the frequency measurement range A and B determined by the amplitude data based on the frequency characteristics of the equalizer 10 are divided into two cycles. Divide the period into 8 equal parts from ■ to ■.

The range of A corresponds to e of the amplitude information QA (I>0, Q>0), and the range of QA corresponds to d (I<0, Q<0), and QA is ■(
I>0, Q<0).

Next, the range of B is QA is the range of c, and ■(
I>0, Q>0), and QA is ■,■(I<
0, Q<0), and QA is ■(I>0, Q<0) in the range of a.
0).

The frequency measurement ranges A, B and I/I determined by the amplitude data determined by the frequency characteristics of the equalizer 10 are
The specific correspondence relationship with the frequency resolution of Q video is as follows. As mentioned above, the equalizer 10 determines the frequency measurement range between two periods, which is twice the conventional example, based on its frequency characteristics, so The bandpass filter 2 for determination is no longer necessary, and the resolution for A and B is 1/8 times that of the conventional method.

Therefore, the I/Q video system is used as a frequency accurate measurement system, the amplitude data system is used as a frequency coarse measurement system, and the uncertainties of the frequency accurate measurement system are corrected by the frequency coarse measurement system to obtain high resolution.

Next, the output bits inputted to the frequency calculation circuit 13 as frequency data from the frequency precision measurement system and the coarse measurement system will be described. The frequency division band divided into eight equal parts of the I/Q video is expressed in bits as shown below, and the frequency is determined as frequency position data. ■ A, I>0, Q>0 ■ B, I>0, Q>
0 ■ A, I < 0, Q > 0 ■ B, I < 0, Q
>0 ■ A, I < 0, Q < 0 ■ A, I < 0,
Q<0 ■ A, I>0, Q<0 ■ A, I>0
, Q<0 or more, each frequency position is displayed as a bit and inputted to the frequency calculation circuit 13, where the code is converted and the frequency measurement is completed.

Next, another embodiment of the present invention will be explained based on the drawings. FIG. 3 is a block diagram of a frequency measurement circuit according to another embodiment of the present invention, in which 14 is an I/Q video frequency calculation circuit, and other symbols are the same as in the above embodiment. FIG. 4 is an I/Q video polar diagram of the present invention. Z is the I/Q video vector and θ is the phase angle.

Next, the operation will be explained. From Figure 3, RF
The operation in which an RF signal is input from the input signal terminal 1 and an I/Q video is output from the phase discrimination circuit 5 is the same as in the previous embodiment.

The output I/Q videos are each quantized by the A/P converter 12, and Z,

By calculating [Equation 3], the amplitude data of the equalizer 10 can be obtained from Z and the quadrant in the same manner as in FIG.

In both of the above embodiments, an equalizer 10 is added to the input side of the I/Q phase discriminator circuit 5 to provide frequency characteristics, but a bandpass filter for determining the measurement band is used. The same effect can be obtained even if the divider 2 or the divider 3 has similar frequency characteristics.

[0026]

[Effects of the Invention] As described above, according to the present invention, the I/Q video frequency precision measurement system is configured to perform corrected measurement using the amplitude data frequency coarse measurement system, so it can be used for wideband measurement with a simple circuit configuration. This also has the effect of providing a device with high resolution.

[Brief explanation of the drawing]

FIG. 1 shows a frequency measuring device that is an embodiment of the present invention.

FIG. 2 is an explanatory diagram of the operation of an embodiment of the present invention.

FIG. 3 is a block diagram of a frequency measuring device according to another embodiment of the invention.

FIG. 4 is a polar coordinate diagram of another embodiment of the invention.

FIG. 5 is a block diagram of a conventional frequency measurement device.

FIG. 6 is an output video waveform diagram of a conventional I/Q phase discrimination circuit.

[Explanation of symbols]

5 I/Q phase discrimination circuit 6 Zero cross slicer 7 Frequency calculation circuit 10 Equalizer 11 Adder 12 A/D converter 13 Frequency calculation circuit 14 Frequency calculation circuit In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An I/Q phase discrimination circuit that discriminates the phase of an RF signal and outputs an I/Q video, a zero cross slicer that quantizes the I/Q video output, and converts the I/Q quantized output into frequency data. In the frequency measuring device, the frequency measuring device is equipped with an equalizer having a certain frequency characteristic provided before the phase discrimination circuit, and a frequency characteristic of the equalizer provided after the phase discrimination circuit. 1. A frequency measurement device comprising: a detection circuit for determined video amplitude data; and a frequency calculation circuit for calculating an input frequency from the video amplitude data and the I/Q video quantized output.