KR100980344B1 - Apparatus and method for generating reference frequency in a communication systems - Google Patents

Apparatus and method for generating reference frequency in a communication systems Download PDF

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KR100980344B1
KR100980344B1 KR1020100023768A KR20100023768A KR100980344B1 KR 100980344 B1 KR100980344 B1 KR 100980344B1 KR 1020100023768 A KR1020100023768 A KR 1020100023768A KR 20100023768 A KR20100023768 A KR 20100023768A KR 100980344 B1 KR100980344 B1 KR 100980344B1
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South Korea
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frequency
sampling frequency
dds
reference frequency
control signal
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KR1020100023768A
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Korean (ko)
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김정한
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삼성탈레스 주식회사
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
    • H03D7/00—Transference of modulation from one carrier to another, e.g. frequency-changing
    • H03D7/16—Multiple-frequency-changing
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
    • H03L7/00—Automatic control of frequency or phase; Synchronisation
    • H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
    • H03L7/08—Details of the phase-locked loop
    • H03L7/10—Details of the phase-locked loop for assuring initial synchronisation or for broadening the capture range
    • H03L7/107—Details of the phase-locked loop for assuring initial synchronisation or for broadening the capture range using a variable transfer function for the loop, e.g. low pass filter having a variable bandwidth
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
    • H03D2200/00—Indexing scheme relating to details of demodulation or transference of modulation from one carrier to another covered by H03D
    • H03D2200/0041—Functional aspects of demodulators
    • H03D2200/0054—Digital filters

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Stabilization Of Oscillater, Synchronisation, Frequency Synthesizers (AREA)

Abstract

The present invention relates to a reference frequency generating device and method in a communication system, and more particularly, to a reference frequency generating device and method in a communication system for improving the accuracy of the frequency output from a direct digital synthesizer. To this end, the present invention provides a method for generating a reference frequency in a communication system, comprising: synthesizing a reference frequency and a first control signal for setting to the reference frequency, generating a first sampling frequency, and performing low pass filtering; Synthesizing the first sampling frequency and the first control signal to generate a second sampling frequency, band pass filtering, synthesizing the band pass filtered second sampling frequency and the second control signal, and And generating the reference frequency by decomposing the synthesized sampling frequency through the frequency turning word.

Figure R1020100023768

Description

Apparatus and method for generating reference frequency in communication system {APPARATUS AND METHOD FOR GENERATING REFERENCE FREQUENCY IN A COMMUNICATION SYSTEMS}

The present invention relates to a reference frequency generating device and method in a communication system, and more particularly, to a reference frequency generating device and method in a communication system for improving the accuracy of the frequency output from a direct digital synthesizer.

In general, a frequency synthesizer in a communication system is used as a local oscillator when converting a radio frequency (RF) into an intermediate frequency (IF) or an intermediate frequency into a radio frequency, and a transmission / reception system having multiple channels. This function is to select the desired channel from. These frequency synthesizers can be divided into direct analog synthesizers, indirect frequency synthesizers, and direct digital synthesizers (DDS) according to new frequency synthesis methods. The direct analog frequency synthesizer synthesizes a desired frequency by mixing, filtering, and algebraic calculation, and the most commonly used method of indirect frequency synthesis is PLL (Phase Locked Loop).

The direct digital synthesis method is a method of obtaining an analog sine wave signal using digital circuits such as an accumulator and a ROM. Direct digital synthesizers are also referred to as Direct Digital Frequency Synthesizer (DDFS), Digital Sine Synthesizer (DSS), or Numerical Controlled Oscillator (NCO). DDS is currently used in satellite communications, radar, instruments, and medical devices. As spread spectrum communication, it is widely used in systems requiring high frequency resolution and fast lock time.

Such a direct digital synthesizer is generally used in a frequency agile system to improve frequency resolution. In this case, the resolution of the direct digital synthesizer is determined by the DDS input sampling frequency / 2 frequency tuning word bits . Frequency tuning word mainly uses 24bits, 28bits, 32bits, 48bits. In addition, in order to reduce the DDS output frequency error, the input sampling frequency of the direct digital synthesizer must be input according to the output frequency of the direct digital synthesizer up to several Hz units, and it is difficult to adjust the unit to the Hz unit using a general oscillator element.

1 is a block diagram showing a conventional reference frequency generator.

As shown, the conventional reference frequency generator includes a fixed frequency synthesizer 102 for receiving a reference frequency and generating a sampling frequency, and a PIC (Programmable Interrupt) for inputting DDS_CLOCK, DDS_DATA, and DDS_ENABLE CONTROL SIGNAL to the fixed frequency synthesizer 102. controller, a low pass filter 106 for low-passing the input sampling frequency output from the fixed frequency synthesizer 102, and a frequency output through the low pass filter 106 for DDS_CLOCK. And a direct digital synthesizer 108 for generating analog sinusoids by frequency decomposition via DDS_DATA, DDS_IO UPDATE CONTROL SIGNAL.

However, in the conventional reference frequency generator, the resolution of the DDS is determined by the DDS input sampling frequency, and when the output frequency is used in a wide frequency range in the same step, the output frequency of the DDS generates a constant frequency error. However, since the frequency tuning word that controls the output frequency of the direct digital synthesizer is not constant, it is necessary to add different weighting factors to the calculated frequency tuning word from the output frequency of a specific direct digital synthesizer. have.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and provides a reference frequency generating device and method in a communication system for improving the accuracy of a frequency directly output from a digital synthesizer.

In accordance with an aspect of the present invention, a method for generating a reference frequency in a communication system includes: generating a first sampling frequency by combining a reference frequency and a first control signal for setting to the reference frequency, and performing low pass filtering; And generating a second sampling frequency by synthesizing the filtered first sampling frequency and the first control signal, and performing band pass filtering, and synthesizing the band pass filtered second sampling frequency and the second control signal. And decomposing the synthesized sampling frequency through a frequency tuning word to generate a reference frequency.

In addition, the present invention for achieving the above-mentioned is a reference frequency generator in a communication system, a fixed frequency synthesizer for generating a first sampling frequency by combining a reference frequency and a first control signal for setting to the reference frequency; A first filter unit for low-pass filtering the generated first sampling frequency, a first direct digital synthesizer for synthesizing the filtered first sampling frequency and the first control signal to generate a second sampling frequency, and A second filter unit for band-pass filtering the generated second sampling frequency, the band-pass filtered second sampling frequency and a second control signal, and decomposing the synthesized sampling frequency through a frequency tuning word to obtain a reference frequency. And a second direct digital synthesizer for generating.

As described above, the present invention provides an apparatus and method for the reference frequency generation in a communication system, thereby lowering the output frequency of the fixed frequency synthesizer to improve phase noise for the final output. In addition, the present invention can use a frequency higher than the input sampling frequency by using the output image signal of the direct digital synthesizer, the output frequency by using the frequency of the image signal of the first direct digital synthesizer as the sampling frequency of the direct digital synthesizer for the final output It has the effect of improving the accuracy.

1 is a block diagram showing a conventional reference frequency generator.
2 is a block diagram illustrating a reference frequency generator according to an exemplary embodiment of the present invention.
Figure 3 is an exemplary view showing a frequency output from the direct digital synthesizer when a direct digital synthesizer according to an embodiment of the present invention.
4 is a flowchart illustrating a reference frequency generation process according to an embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings will be described in detail the operating principle of the preferred embodiment of the present invention. In the following description of the present invention, detailed descriptions of well-known functions or configurations will be omitted if it is determined that the detailed description of the present invention may unnecessarily obscure the subject matter of the present invention. In addition, terms to be described below are terms defined in consideration of functions in the present invention, and may be changed according to a user, a user's intention or custom. Therefore, the definition should be made based on the contents throughout the specification.

2 is a block diagram illustrating a reference frequency generator according to an exemplary embodiment of the present invention.

As shown, the reference frequency generator according to the embodiment of the present invention synthesizes the first reference frequency by combining the input reference frequency and the DDS_CLOCK, DDS_DATA, DDS_ENABLE CONTROL SIGNAL generated from the first PIC (Programmable Interrupt Controller, 204) A fixed frequency synthesizer 202 to generate, a first filter unit 206 for low-pass filtering the first sampling frequency generated by the fixed frequency synthesizer 202, and the first filter unit 206 to filter A first direct digital synthesizer 208 for synthesizing the received frequency and the DDS_CLOCK, DDS_DATA, and DDS_ENABLE CONTORL SIGNAL input from the second PIC to generate a second sampling frequency, and a first generated through the first direct digital synthesizer 208. The second filter unit 212 for band-pass filtering the sampling frequency, and the DDS_CLOCK, DDS_DATA, DDS_IO UPDATE CONTROL SIGNAL synthesized with the frequency filtered by the second filter unit 212 and output the DDS. And a second direct digital synthesizer 214 to generate frequencies.

In the reference frequency generator according to the present invention described above, the first and second PICs 204 and 210 are controllers that provide various modes of operation and are used for interrupts. These PICs are programmed with a method of initiating a plurality of PICs, a method of accepting interrupts, and a method of informing the control unit that generally controls the reference frequency generator about the interrupts received.

Hereinafter, a reference frequency generator according to an embodiment of the present invention will be described as an example.

If the 10MHz reference frequency is input to the fixed frequency synthesizer 202, the fixed frequency synthesizer 202 receives DDS_CLOCK, DDS_DATA, and DDS_ENABLE CONTROL SIGNAL from the 10MHz reference frequency and the first PIC 204 and synthesizes the corresponding frequency. The first filter unit 206 performs low pass filtering. The frequency filtered through the first filter unit 206 has about 300 MHz. The first direct digital synthesizer 208 synthesizes the filtered 300MHz frequency and the DDS_CLOCK, DDS_DATA, and DDS_ENABLE CONTROL SIGNAL input from the second PIC 210 to output a sampling frequency of about 390MHz (Fundamental frequency: about 90MHz). do. More specifically, the image frequency has 390.4515723930672 MHz (Fundamental frequency: 90.4515723930672 MHz). And, since the maximum frequency that can be processed in the second direct digital synthesizer 214 is generally 400 MHz, the second filter unit 212 filters the sampling frequency of 390 MHz to remove Fundamental frequency and other unnecessary image frequencies. do. That is, the second filter part is a band pass filter passing only a desired frequency. The second direct digital synthesizer 214 generates a frequency of 390 MHz / 2 32 steps according to the input DDS_CLOCK, DDS_DATA, and DDS_IO UPDATE CONTROL SIGNAL.

In other words, the present invention uses an image frequency having frequency accuracy in Hz or less output from the first direct digital synthesizer 208 as the sampling frequency of the second direct digital synthesizer 204. In addition, although the present invention has described a reference frequency generator in which only two direct digital synthesizers are configured (first and second direct digital synthesizers), this is only an embodiment, and a plurality of direct digital synthesizers may be configured. Table 1 shows an image frequency output from the first direct digital synthesizer when the sampling frequency (Fs_1) of the first direct digital synthesizer is 300 MHz and the Fundamental frequency (Ff) output from the first direct digital synthesizer is set to 90 MHz. It is shown.

Primary image frequency (MHz) Secondary Image Frequency (MHz) Third Image Frequency (MHz) 4th image frequency (MHz) 5th image frequency (MHz) Image composition Fs_1-Ff Fs_1 + Ff 2Fs_1-Ff 2Fs_1 + Ff 3Fs_1-Ff Image frequency 209 MHz 390.4515723930672MHz 509.5484276069328MHz 690.4515723930672MHz 809.5484276069328MHz

In Table 1, the unit of the image frequency is MHz, and the decimal point is omitted for convenience, but the correct frequency output from the output frequency of the second direct digital synthesizer is 209.5484276069328 MHz for the primary image frequency, and 390.4515723930672MHz, 509.5484276069328MHz for the third image frequency, 690.4515723930672MHz for the fourth image frequency, and 809.5484276069328MHz for the fifth image frequency. 3 is an exemplary diagram showing Fundamental and image frequencies output from the first direct digital synthesizer as shown in Table 1 above.

At this time, the output frequency of the fixed frequency synthesizer 202 determines the resolution and the step of the output frequency of the first direct digital synthesizer, and the output frequency of the first direct digital synthesizer determines the resolution and the step of the second direct digital synthesizer. Thus, the resolution and step relative to the final output frequency of the second direct digital synthesizer are determined by determining the output frequency of the first direct digital synthesizer. In addition, the output frequency of the fixed frequency synthesizer should select a fixed frequency synthesizer output that can use the lowest sampling frequency among the image signals available in Table 1, thereby outputting a frequency output from the second direct digital synthesizer. It is possible to improve the phase noise of.

Hereinafter, when the secondary image signal of the first direct digital synthesizer is used as the sampling frequency of the second direct digital synthesizer, the resolution and output frequency steps are as follows.

The output frequency can be selected with the accuracy of 0.090909090915943309664726257324219Hz with the resolution of 390.4515723930672MHz / 2 32 , and if the frequency tuning word step is taken to 11 ((390MHz / 2 32 ) × 11), the output frequency with the precision of 1.0000000000753764063119888305664Hz can be obtained. have.

4 is a flowchart illustrating a reference frequency generation process according to an embodiment of the present invention.

Hereinafter, a reference frequency generation process according to an embodiment of the present invention will be described in detail with reference to FIG. 4.

When the reference frequency is input, the first reference frequency is generated by synthesizing the input reference frequency with a plurality of control signals (S401 and S403). The plurality of control signals include DDS_CLOCK, DDS_DATA, and DDS_IO UPDATE. These control signals are used to set the output frequency, and the sampling frequency is generated using this control signal. The low pass filtering is performed on the first sampling frequency generated in step S403 (S405). A second sampling frequency is generated by combining the low pass filtered first sampling frequency and the plurality of control signals (S407). The plurality of control signals synthesized in S403 and the plurality of control signals synthesized in S407 may be the same or different.

In operation S407, the second sampling frequency generated in step S407 is band pass filtered. The band pass filtering refers to filtering to pass only a desired frequency band. A plurality of control signals are synthesized with the band pass filtered second sampling frequency. The second sampling frequency is decomposed using the frequency tuning word and an output frequency is generated (S411). That is, the bandpass filtered second sampling frequency is divided by two frequency tuning word bits to generate an output frequency.

Claims (9)

A method of generating a reference frequency in a communication system,
Synthesizing a reference frequency and a first control signal for setting to the reference frequency, generating a first sampling frequency, and performing low pass filtering;
Synthesizing the filtered first sampling frequency and the first control signal to generate a second sampling frequency and performing band pass filtering;
Synthesizing the band pass filtered second sampling frequency and a second control signal;
Decomposing the synthesized sampling frequency through a frequency tuning word to generate a reference frequency,
The generated first sampling frequency determines the resolution and the step of the second sampling frequency, and the generated second sampling frequency determines the resolution and the step of the synthesized sampling frequency.
The method of claim 1, wherein the generating of the reference frequency
And generating the reference frequency by dividing the synthesized sampling frequency by two frequency tuning word bits .
The method of claim 1, wherein the first control signal is
A reference frequency generation method comprising: DDS_CLOCK, DDS_DATA, and DDS_ENABLE CONTORL SIGNAL.
The method of claim 1, wherein the second control signal is
A reference frequency generation method comprising DDS_CLOCK, DDS_DATA, and DDS IO UPDATE.
The method of claim 2, wherein the reference frequency is
A method of generating a reference frequency characterized by having an accuracy of 1 Hz or less.
A reference frequency generator in a communication system,
A fixed frequency synthesizer for synthesizing a reference frequency and a first control signal for setting to the reference frequency to generate a first sampling frequency;
A first filter unit for low pass filtering the generated first sampling frequency;
A first direct digital synthesizer configured to synthesize the filtered first sampling frequency and the first control signal to generate a second sampling frequency;
A second filter unit for band-pass filtering the generated second sampling frequency;
And a second direct digital synthesizer for synthesizing the band pass filtered second sampling frequency and the second control signal and decomposing the synthesized sampling frequency through a frequency tuning word to generate a reference frequency.
The generated first sampling frequency determines the resolution and the step of the second sampling frequency, and the generated second sampling frequency determines the resolution and the step of the synthesized sampling frequency.
The method of claim 6, wherein the second direct digital synthesizer
And generating the reference frequency by dividing the synthesized sampling frequency by two frequency tuning word bits .
The method of claim 6, wherein the first control signal is
A reference frequency generator comprising DDS_CLOCK, DDS_DATA, and DDS_ENABLE CONTROL SIGNAL.
The method of claim 6, wherein the second control signal is
A reference frequency generating device comprising DDS_CLOCK, DDS_DATA, and DDS IO UPDATE.
KR1020100023768A 2010-03-17 2010-03-17 Apparatus and method for generating reference frequency in a communication systems KR100980344B1 (en)

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100579680B1 (en) * 1997-11-19 2006-05-15 에릭슨 인크. Simplified reference frequency distribution in a mobile phone
KR100918793B1 (en) * 2004-11-30 2009-09-25 에이에이아이 코포레이션 Phase Persistent Agile Signal Source Method, Apparatus, and Computer Program Product

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100579680B1 (en) * 1997-11-19 2006-05-15 에릭슨 인크. Simplified reference frequency distribution in a mobile phone
KR100918793B1 (en) * 2004-11-30 2009-09-25 에이에이아이 코포레이션 Phase Persistent Agile Signal Source Method, Apparatus, and Computer Program Product

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