KR100233552B1 - A frequency measuring accuracy upgrading method and a device for upgrading same - Google Patents

Abstract

The present invention relates to a method and apparatus for augmenting frequency measurement accuracy in digital mobile communication, and simultaneously mixing a measurement frequency of a UUT (Unit Under Test) equipment 1 and a reference frequency of a DDS (Direct Digital Synthesizer) equipment (2). By applying and mixing in (3) so that only low frequency components are left, and then these low frequency components are sequentially passed through the low pass filter (4), the amplifier (5), the counter (6), and the controller (7). The present invention relates to a method for enhancing frequency measurement accuracy that can improve frequency measurement accuracy by displaying a frequency error to be measured in (8).

Description

A frequency measuring accuracy upgrading method and a device for upgrading same}

The present invention is, more particularly, the accuracy of the method, a method capable of enhancing the frequency measurement accuracy to precisely measure the frequency that is received so as to suppress the generation of noise, the frequency measurement accuracy enhancement in a communication system such as a digital mobile communication ^{10- The present} invention relates to a method for enhancing the frequency measurement accuracy that can greatly improve the measurement accuracy in measuring a CDMA or TDMA communication frequency requiring about ¹¹ Hz.

In the case of digital mobile communication, which is becoming more common in recent years, frequency measurement accuracy for synchronization signals is required to be about 10 ^-11 in order to improve communication sensitivity. However, the frequency measuring equipment up to now has a measurement accuracy of only about 10 ^-8 , which is far short of the frequency measuring precision required in the above-mentioned digital mobile communication. Therefore, the existing measuring equipment could not measure the minute frequencies of about 10 ^-11 used in digital mobile communication. Therefore, in order to measure the fine frequencies of about 10 ^-11 used in the digital mobile communication, the frequency measurement precision of the reference timing source must be more accurate than 10 ^-11 and the resolution of the frequency measurement equipment ( Resolution should be less than 10 ^-11 .

Therefore, ^10-12, or by performing a mixing (Mixing) process that is, the frequency zooming (. Zooming Freq) of the frequency component to be measured in order to meet the frequency measurement accuracy ^(10-11) required in the digital mobile communication ^{10- Up to 13} minute frequency components can be measured. However, in order to measure several types of measurement frequencies used in mobile communication, such as 10 MHz, 1.544 MHz, 2.048 MHz, etc., using a single measuring instrument, the number of measurement frequencies corresponding to the inputted frequency is corresponding. As the reference frequency is required, the number of equipment for applying the reference frequency is also required, resulting in high cost of the measuring equipment.

Accordingly, the present invention uses a single clock pulse source signal, that is, a programmable frequency source signal of a direct digital synthesizer (hereinafter simply referred to as a DDS device) as a reference frequency signal, and this reference frequency signal is used as a fine noise. The frequency signal of UUT (test equipment) in the synthesized state is compared and measured simultaneously through the mixer, so that only low frequency components remain, and the low frequency components are measured again to improve the frequency measurement accuracy. It aims to provide.

In addition, the present invention in order to accurately measure the frequency used in the communication system, such as digital mobile communication, by changing the reference frequency signal and the measurement frequency signal applied to the mixer to apply to the mixer even if the measurement frequency changes It is another object of the present invention to provide a method for enhancing frequency measurement accuracy that can eliminate the need to change the frequency.

1 is a block diagram schematically showing an apparatus for enhancing frequency measurement precision according to the present invention;

Fig. 2 is a block diagram showing a method of measuring a frequency by inputting a measurement frequency and a reference frequency into the mixer in Fig. 1, respectively.

3 is a view illustrating a comparison between the measurement precision according to the conventional method and the measurement precision according to the present invention.

* Explanation of symbols for main parts of the drawings

1.UUT 2.DDS

3. Mixer 4. Low Pass Filter

5. Amplifier 6. Counter

7. Controller 8. Display

fr. Reference frequency fu. Measuring frequency

f _D. Fixed frequency

Hereinafter, with reference to the accompanying drawings will be described the configuration of the present invention and the resulting effects.

First, referring to Figure 1 will be described the overall structure of the frequency measurement precision enhancing apparatus according to the present invention.

As shown in Fig. 1, the frequency measurement precision increasing apparatus of the present invention comprises a mixer 3, a low pass filter 4, an amplifier 5, a counter 6, a controller 7 and a display 8, and a UUT. (Unit Under Test) by applying the measurement frequency signal of the equipment (1) and the reference frequency signal of the DDS (Direct Digital Synthesizer) equipment (2) at the same time to the mixer (3), the mixer 3 causes the measurement frequency and reference By comparing the frequencies, only the low frequency signal, which is a noise component, remains, and the harmonic components are removed from the low frequency filter 4 through the low pass filter 4, and the low frequency components are amplified through the amplifier 5 to drive the counter 6, and then It is applied sequentially to the controller 7 of the stage to finally display the frequency error to be measured on the display 8.

In more detail, as shown in the drawing, in the UUT device 1, which is a test equipment, the measurement frequency signal fu = f + fe is applied to the mixer 3 as a + signal, and in the DDS device 2, the reference frequency signal ( fr = f + Δf) is applied to the mixer 3 as a-signal. Then, the respective measured frequency signals fu = f + fe and the reference frequency signals fr = f + Δf applied to the mixer 3 are compared in the mixer 3 for fu-fr processing. Then, f of the measurement frequency and f of the reference frequency cancel each other out, leaving only the low frequency signal fe-Δf. This low frequency signal remains as a harmonic (harmonic component) component of fe-Δf. The component is expressed as follows.

fe-Δf = (fe-Δf) + 2 (fe-Δf) + 3 (fe-Δf) +... … .

The harmonic components 2 (fe-Δf) + 3 (fe-Δf) +... Of the low frequency signal fe-Δf are removed through the low pass filter 4. Subsequently, this signal is moved to the amplifier 5, and the amplifier 5 amplifies the low frequency signal fe-Δf so as to increase the signal level so that the counter 6 can be triggered. In the counter 6, when zero-crossing reading is performed, a dc offset is performed so as not to be triggered with respect to the noise input to prevent the noise from driving the counter 6. The signal fe-Δf that has passed through the counter 6 is applied to the controller 7. Then, the controller 7 measures this signal fe-Δf and adds Δf to the measured value to perform fe-Δf + Δf. As a result, only the frequency error fe to be measured is displayed on the display 8. In the above description, the value of Δf is about 100 Hz as an arbitrarily selected offset frequency, and when the value of Δf is too small, filter design becomes difficult. As described above, the frequency measurement accuracy can be greatly improved by measuring the frequency error component again.

In the figure, fe is a frequency error to be measured, and the signal f + fe input from the UUT 1 to the mixer 3 is a measurement frequency signal of 2.048 MHz, 1.544 MHz, and 10 MHz, which are commonly used in the digital mobile communication field. to be. In order to measure these various frequencies with a single measuring device, several reference frequencies are usually required, but in that case, a corresponding reference frequency is required for each measurement frequency. is not a method, in a stable frequency source in the present invention (atomic frequency source; atomic frequency STD) from a fixed frequency (f _D) the programmable frequency causes die Rotaract digital synthesizer (DDS) is applied to selected and outputting a reference frequency in I'm trying to.

Cesium or Rubidium should be used as the atomic frequency generator. In the frequency generator using cesium or rubidium, frequencies of 10 MHz, 5 MHz, and 1 MHz are typically generated. Therefore, in the DDS 2, various frequencies generated from an atomic frequency generator using cesium or rubidium as a programmable frequency source are input. Accordingly, when a word necessary for the DDS 2 is input to select a corresponding frequency from the DDS 2 and set it as a fixed frequency f _D for a reference frequency, the DDS 2 In the reference frequency required is output. Therefore, even when the measurement frequency from the UUT 1 changes to either 1.544 MHz or 2.048 MHz, the corresponding reference frequency can be selectively applied from the DDS 2. Therefore, it is possible to measure accurately with one measuring device. For example, when the measurement frequency (fu) in the UUT (1) is 2.48 MHz + fe, when the reference frequency (fr) output from the DDS (2) is 2.048 MHz + 10 Hz, finally only fe Since only low frequency components remain, frequencies can be measured with high precision up to 10 ^-13 .

That is, the measurement precision according to the conventional method and the measurement precision according to the present invention will be described with reference to FIG. 3 as follows. As shown in the figure, in the case of measuring 2,048,000.00001Hz by the conventional method, the final measured value is 2,048,000Hz as shown in (a) and its accuracy is 1/2048000, that is, 4.88 × 10 ^-7 . When measuring the low frequency signal component Δf + fe (Δf = 10Hz, fe = 0.00001Hz) extracted using the mixer of the present invention, the measured value is 10.00001Hz as shown in (b) and the measurement precision is 0.00001 / 2048000 = 4.88 x 10 ^-12 . Therefore, according to the present invention, it is possible to remarkably increase the measurement accuracy with respect to frequency.

On the other hand, when DDS is used, the fixed frequency f _D input to the DDS must be f _D ≥2fr. However, since the maximum frequency of the atomic frequency source is 10MHz, the output frequency of the DDS does not exceed 5MHz. Therefore, in this state, the constraint that the measurement is possible only when the measurement frequency of the UUT 1 is 5MHz or less is given. In order to solve the above limitation condition, in the present invention, as shown in Fig. 2, the measurement frequency signal fu (f + fe) from the UUT 1 in Fig. 1 is applied to the DDS 2, and the reference frequency signal ( fr) proposes a method of applying ÷ N. According to this method, the frequency of f + fe + Δf is applied to the mixer 3 as the − signal from the DDS 2, and the reference frequency fr is divided into N from ÷ N so that only f is the + signal as the mixer 3. Is applied. Therefore, in the mixer 3, the fr-fu process, that is, the f- (f + fe + Δf) process, is performed while the reference frequency fr and the measurement frequency fu output from the DDS 2 are compared. Then, the high frequency components f and f of the synthesized signals cancel each other out and only the low frequency signal component of-(fe + Δf) remains. This low frequency signal passes through the low pass filter 4 and is subsequently applied to the controller 7 via the amplifier 5 and the counter 6. Then, the controller 7 measures the low frequency signal (− (fe + Δf) and then adds + Δf to the measured value, so that only -fe, which is the frequency error component to be measured, remains. In the above, when the measurement frequency signal f _u = f + fe of the UUT 1 is applied to the DDS 2, and the reference frequency signal f _r is directly input to the mixer 3 with N = 1. Since the output frequency of the DDS (2) must satisfy the condition of f _u ? 2 (f + fe +? F), a high frequency of 20 MHz or more can be measured. In addition, N = 2, 3, 4,... … In the case of dividing the reference frequency by, for example, the frequency can be measured 1 / N times lower than the reference frequency. Although only the frequency component of -fe is left in this method, this is taken to be substantially equal to fe. Therefore, frequency measurement accuracy can be greatly improved by measuring the frequency error component again.

When the frequency is measured by the method shown in FIG. 2, the measured frequency signal of the UUT can be measured even if the frequency is N times higher than the reference frequency signal, even if the maximum frequency of the reference atomic frequency generator is 10 MHz. Since the frequency can be measured, the frequency measurement band can be greatly widened.

Therefore, according to the present invention, the measurement frequency and the reference frequency are measured and compared by using a mixer, so that only the low frequency signal is left and measured again, thereby greatly improving the frequency measurement accuracy, and the measurement frequency of the UUT and the reference frequency applied to the DDS are different from each other. If inputted into the mixer, the reference frequency does not need to be changed even if the measurement frequency of the UUT changes, so a single device is sufficient, which can greatly reduce the cost according to the configuration of the device.

Claims (2)

In the frequency measurement accuracy enhancement method for measuring various types of measurement frequencies used in mobile communication such as 10MHz, 1.544MHz, 2.048MHz, The measurement frequency of the UUT and the reference frequency of the DDS are simultaneously applied as the (+) signal and the (-) signal of the mixer 3 and mixed to leave only the low frequency signal, which is a fine frequency component, and the low pass filter 4 and the amplifier ( 5) and a method for enhancing the frequency measurement precision, characterized in that by applying to the controller (7) through the counter (6) to improve the measurement accuracy for the frequency. The method of claim 1, And increasing the measurement frequency of the UUT and the reference frequency of the DDS and applying the same to the mixer (3).