Abstract:
There is provided a frequency correcting system including an oscillator outputting a target signal having an oscillating frequency, and a frequency corrector comparing the frequency of the target signal with the frequency of the reference signal and correcting the oscillating frequency to match a frequency of a predetermined reference signal, thereby automatically correcting an error in the oscillating frequency occurring during the manufacturing processes to provide precise and stable oscillating frequency.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2014-0086166, filed on Jul. 9, 2014, entitled “Frequency Correction System and Correcting Method Thereof” which is hereby incorporated by reference in its entirety into this application. 
       BACKGROUND 
       [0002]    The present disclosure relates to a frequency correction system and a correcting method thereof. 
         [0003]    Many electronic devices often require signals having frequency. For example, all digital systems require clock signals having frequency, and many analog systems require radio frequency (RF) signals, local oscillation signals, or the like. Moreover, as IT technology such as wireless mobile communications evolves recently, more precise and stable frequency is required more often. 
         [0004]    Frequency quality of frequency oscillators for generating frequency differs depending on the fundamental circuits and material properties thereof. Due to such structural issues, the oscillators cannot always maintain the same quality, although it may slightly differ depending on the type of oscillators. 
         [0005]    Variations in quality of oscillating frequency generated by such frequency oscillators occur, because, during the semiconductor processes, the characteristic of a transistor in an integrated circuit (IC) may be changed or errors may occur in resistance of resistors and capacitance of capacitors. 
         [0006]    In other words, if the characteristic of a transistor of an oscillator or an integrated circuit is changed, or if the resistance of a resistor and the capacitance of a capacitor have a different value from an initially designed value, the oscillating frequency generated from the oscillator becomes different from the initially designed target frequency, and thus there exist variations. 
         [0007]    In an integrated circuit having an oscillator, if the oscillator has large variations in oscillating frequency, it restricts the maximum frequency characteristics of the integrated circuit (IC) and applications, so that the chip performance of the integrated circuit becomes lower decreased and the yield is reduced. 
         [0008]    Previously, if a frequency error occurs in a system sensitive to frequency due to process variations, it is necessary to correct the frequency in a separate process. In order to correct to such a frequency error, a method has been used involving measuring oscillation frequencies of frequency oscillators each in individual integrated circuits, calculating an error between the measured oscillating frequencies and the target frequency, and setting the oscillators based on the errors one by one. 
       RELATED ART DOCUMENT 
     Patent Document 
       [0009]    (Patent Document 1) KR1985-0002364 A 
       SUMMARY 
       [0010]    The present disclosure is directed to comparing a frequency of a predetermined external reference signal with an oscillating frequency of a target signal to compute an error value, and then, by a main processor, correcting the oscillating frequency using a setting value corresponding to the error value. Therefore, an aspect of the present disclosure may provide a frequency correction system and a correcting method thereof that automatically correct an error in an oscillating frequency caused by various factors including process variations during the manufacturing a frequency oscillator. 
         [0011]    According to an aspect of the present disclosure, a frequency correction system may include an oscillator outputting a target signal having an oscillating frequency, first and second counters counting the frequency of the target signal and a frequency of a predetermined reference signal, a comparator comparing first and second count values to calculate an error value, a look-up table having stored a correction value corresponding to the error value, a main processor computing a setting value, and a memory. 
         [0012]    According to another aspect of the present disclosure, a frequency correcting method may include detecting a target signal from an oscillator, comparing an oscillating frequency of the target signal with a frequency of a reference signal and correcting a frequency of the target signal using a first error value calculated, and determining whether correction of the oscillating frequency of the target signal has been completed by comparing a second error value calculated based on the oscillating frequency of the corrected target signal and the frequency of the reference signal with a predetermined first threshold value. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0013]    The above and other aspects, features and other advantages of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0014]      FIG. 1  is a block diagram of a frequency correction system according to an exemplary embodiment of the present disclosure; 
           [0015]      FIG. 2  is a diagram of a memory according to an exemplary embodiment of the present disclosure; 
           [0016]      FIG. 3  is a flow chart for illustrating an overall frequency correcting method according to an exemplary embodiment of the present disclosure; 
           [0017]      FIG. 4  is a flowchart for illustrating a process of selecting a correction mode and a normal mode according to an exemplary embodiment of the present disclosure; 
           [0018]      FIG. 5  is a flow chart for illustrating a process of correcting an oscillating frequency according to an exemplary embodiment of the present disclosure; 
           [0019]      FIG. 6  is a flow chart for illustrating a process of determining whether correction of an oscillating frequency is completed according to an exemplary embodiment of the present disclosure; 
           [0020]      FIG. 7  is a flow chart for illustrating an oscillating frequency correcting method in a normal mode according to an exemplary embodiment of the present disclosure; and 
           [0021]      FIG. 8  is a diagram showing timings in a correction mode according to an exemplary embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    The objects, features and advantages of the present disclosure will be more clearly understood from the following detailed description of the exemplary embodiments taken in conjunction with the accompanying drawings. Throughout the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant descriptions thereof are omitted. Further, in the following description, the terms “first,” “second,” “one side,” “the other side” and the like are used to differentiate a certain component from other components, but the configuration of such components should not be construed to be limited by the terms. Further, in the description of the present disclosure, when it is determined that the detailed description of the related art would obscure the gist of the present disclosure, the description thereof will be omitted. 
         [0023]    Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. 
         [0024]    As shown in  FIG. 1 , a frequency correction system according to an exemplary embodiment of the present disclosure includes an oscillator  10  outputting a target signal including an oscillating frequency f 1 , and a frequency corrector  100  comparing the oscillating frequency f 1  of the target signal with a frequency f 2  of a predetermined reference signal to match the oscillating frequency f 1  of the target signal to the frequency f 2  of the reference signal. 
         [0025]    The oscillator  10  is a device that generates electrical oscillation using an electron tube or a semiconductor. It is disposed inside or outside an integrated circuit to generate an oscillating frequency f 1  for the use in the integrated circuit. 
         [0026]    In addition, the oscillator  10  generates a target signal including an oscillating frequency in the form of a clock signal or converts it into a clock signal to transmit it to a first counter  111 . The oscillator  10  receives a setting value of a main processor  120  and corrects the oscillating frequency f 1  of the target signal according to the setting value. The oscillator  10  may be, but is not limited to, a ring oscillator composed of one or more inverters connected in series. 
         [0027]    The frequency corrector  100  is to correct errors in the oscillating frequency f 1  caused by various factors such as variations in processes of the oscillator  10 . The frequency corrector  100  receives a target signal and a reference signal to calculate a setting value to control parameters of the oscillator  10  and then sends it to the oscillator  10 , thereby correcting the oscillating frequency f 1  of the target signal. The frequency corrector  100  includes an error calculating unit  110  comparing a frequency f 2  of the reference signal with an oscillating frequency f 1  of the target signal to calculate an error value, a main processor  120  computing a setting value based on the error value, and a memory  130  storing the setting value therein. 
         [0028]    The frequency f 2  of the reference signal is a target frequency at the time of designing. It is not necessarily limited to a design target but may be determined as desired by a user. The frequency f 2  of the reference signal is input to a second counter  112  in the form of a clock signal. The reference signal may be input via test equipment at a test set-up stage after manufacturing an integrated circuit. 
         [0029]    The error calculating unit  110  calculates an error value based on the frequency f 2  of the reference signal with the oscillating frequency f 1  of the target signal, and transmits the error value to the main processor  120 . The error calculating unit  110  includes a first counter  111  counting the oscillating frequency f 1  of the target signal to output a first count value, a second counter  112  counting the frequency f 2  of the reference signal to output a second count value, and a comparator  113  comparing the first count value and the second count value to calculate an error value. 
         [0030]    The counters  111  and  112  count the oscillating frequency f 1  of the target signal and the frequency f 2  of the reference signal to output digital values. The counters  111  and  112  store the value of 1 whenever one cycle of a signal elapses. The first counter  111  counts the oscillating frequency f 1  of the target signal. The second counter  112  counts the frequency f 2  of the reference signal. The first and second counters  111  and  112  send their respective count values to the comparator  113  and may be configured as hardware. 
         [0031]    A maximum value to be compared to the second count value refers to a maximum value countable by the counters  111  and  112 . For example, if the second counter  112  is of a 4-bit counter, the counting range is from 0000 to 1111, with the maximum value of 15. The time point when the second count value reaches the maximum value is the reference time point. At this time point, the first and second counters  111  and  112  stop counting and send the first and second count values to the comparator  113 , respectively, for comparison of the first and second count values. 
         [0032]    Because the oscillating frequency f 1  of the target signal may possibly be higher than the frequency f 2  of the reference signal, the first counter  111  has a counting range broader than the counting range of the second counter  112 . 
         [0033]    For example, if the first and second counters  111  and  112  have the same maximum value and the oscillating frequency f 1  of the target signal is higher than the frequency f 2  of the reference signal, the first count value reaches the maximum value before the second count value reaches the maximum value, so that comparison of the count values cannot be carried out accurately. This is because the counting operation is controlled based on the second count value and the maximum value of the second counter  112 . 
         [0034]    Namely, the maximum value of the first counter  111  is set to be larger than that of the second counter  112  in order to obtain the same period for comparison between oscillation frequencies f 1  of different target signals and the frequency f 2  of the reference signal. On the contrary, if the reference time point is set based on the first count value, the maximum value of the second counter has to be larger than that of the first counter. 
         [0035]    The comparator  113  compares the first count value of the oscillating frequency f 1  with the second count value of the frequency of the reference signal frequency to calculate an error value, and sends the calculated error value to the main processor  120 . Additionally, the comparator  113  may be configured as either hardware or software. 
         [0036]    For calculating the error value, the comparator  113  performs division operation using the first count value and the second count value. The error value is 1 if the oscillating frequency f 1  of the target signal is equal to the frequency f 2  of the reference signal. In addition, the comparator  113  may calculate the error value by performing subtraction operation using the first count value and the second count value. In this instance, the error value is zero if the oscillating frequency f 1  of the target signal is equal to the frequency f 2  of the reference signal. 
         [0037]    However, the error value may be calculated by using various methods other than division operation or subtraction operation. Depending on the type of the operation, the error value may be a percentage values instead of an integer value. 
         [0038]    The main processor  120  computes a setting value to control the oscillating frequency f 1  based on the error value and corrects the oscillating frequency f 1  to be matched to the frequency f 2  of the reference signal. In addition, the main processor  120  includes a look-up table  121  in which correction values corresponding to error values are stored. 
         [0039]    The look-up table  121  refers to a collection of results pre-computed for a given operation so as to save processing time since such indexing is faster than performing the given operation. In the look-up table  121 , correction values corresponding to the error values calculated by the error calculation unit are stored. A correction value is selected based on an error value by the error calculating unit  110 . 
         [0040]    The main processor  120  computes a setting value based on the correction value sent from the look-up table  121  to send the setting value to the oscillator  10 . The setting value is used to control parameters determining the characteristic of the oscillating frequency f 1  of the target signal of the frequency oscillator  10 . Upon receiving the setting value, the frequency oscillator  10  changes the parameter to generate a new oscillating frequency f 1 . 
         [0041]    Therefore, according to an exemplary embodiment of the present disclosure, variations in the oscillating frequency f 1  of the target signal are corrected automatically. As a result, deviations in frequency output are reduced, so that reliability of frequency in a system requiring accurate frequency is increased. Accordingly, frequency applied to an integrated circuit approximates to the maximum operating frequency of the integrated circuit to thereby improve the overall performance of the system. 
         [0042]    As shown in  FIG. 2 , the memory  130  stores therein correction completion code, correction failure code and setting values. Specifically, the memory  130  stores the correction completion code at an address if a second error value is smaller than a first threshold value, and stores the correction failure code at an address if the second error value is larger than the first threshold value. If no correction has been made, no code is stored. [ 0034 ] Therefore, if the correction completion code or the correction failure code is stored, it means that the oscillating frequency f 1  is corrected. Storing the correction completion code or the correction failure code is for preventing that a noise occurs in a frequency correction system so that a correction is performed again even though correction has been performed. 
         [0043]    Setting values are stored in the boxes below the box in which the codes are stored. A setting value is stored if the second error value is smaller than the predetermined first threshold value. If a start signal is not applied so that the normal mode is performed, the main processor  120  reads out a stored setting value to send it to the oscillator  10  to thereby correct the oscillating frequency f 1  of the target signal. The memory  130  may be, but is not necessarily limited to, a non-volatile memory such as an EEPROM or a flash memory. 
         [0044]    Hereinafter, a frequency correction method according to an exemplary embodiment of the present disclosure will be described, which includes the above-described elements. In the following description, redundant descriptions of the same or similar elements will be omitted or described briefly. 
         [0045]      FIGS. 3 to 7  are flowcharts for illustrating a frequency correction method. 
         [0046]    As shown in  FIG. 3 , the frequency correction method according to an exemplary embodiment of the present disclosure includes detecting a target signal from the oscillator  10  (S 10 ), and comparing the oscillating frequency f 1  of the target signal with the frequency f 2  of the reference signal to perform a correction mode in which the frequency of the target signal is corrected to be matched to the frequency f 2  of the reference signal. 
         [0047]    The correction mode includes comparing the oscillating frequency f 1  of the target signal with the frequency f 2  of the reference signal and correcting the oscillating frequency f 1  of the target signal using the first error value calculated (S 20 ), and determining whether the correction of the frequency of the target signal has been completed by comparing the second error value calculated based on the corrected target signal and the frequency f 2  of the reference signal with the predetermined first threshold value (S 30 ). 
         [0048]      FIG. 4  is a flowchart for illustrating detecting a start signal to determine a correction mode or a normal mode (S 100 ). The correction mode is selected if the start signal is detected, whereas the normal mode is selected if the start signal is not detected. As described above, the correction mode is a method for correcting the frequency oscillator  10  by computing a setting value with the oscillating frequency f 1  of the target signal and the frequency f 2  of the reference signal. The normal mode is a method for correcting the oscillator  10  using the pre-stored setting values in the memory  130 . 
         [0049]    If the start signal is detected, the correction success code or the correction failure code is detected in the memory  130  (S 110 ). If neither the correction success code nor the correction failure code is detected, the correction mode is performed in which the oscillating frequency of the target signal is corrected using the reference signal. If the correction success code or the correction failure code is detected in the memory  130 , the correction completion signal is output, and the process is completed (S 180 ). Detecting the correction success code or the correction failure code is for preventing malfunction of the frequency correction system due to noise. [ 0   042 ] As illustrated in  FIG. 5 , in the correction mode, the first counter  111  counts the oscillating frequency f 1  of the target signal to output the first count value (S 120 ). The second counter  112  counts the frequency f 2  of the reference signal to output the second count value (S 130 ). At the reference time point when the second count value reaches the predetermined maximum value (S 140 ), the first and second counters  111  and  112  stop operation and the comparator  113  compares the first and second count values. 
         [0050]    In doing so, two count values are compared to each other by performing division operation or subtraction operation to calculate the first error value ( 150 ). If the second count value does not reach the maximum value, it returns to the counting of the oscillating frequency f 1  of the target signal (S 120 ). 
         [0051]    Subsequently, a correction value corresponding to the first error value output from the comparator  113  is selected from the look-up table  121  (S 160 ), and a setting value to control the parameters of the oscillator  10  is computed based on the sent correction value. The computed setting value is sent to the oscillator  10  so that the oscillating frequency f 1  of the target signal is corrected (S 170 ). 
         [0052]    As illustrated in  FIG. 6 , the frequency correction method involves outputting a third count value obtained by counting the frequency of the corrected target signal and a second count value obtained by counting the frequency f 2  of the reference signal (S 190  and S 200 ), determining whether the second count value has reached the maximum value, i.e., the reference time point (S 210 ), comparing the second count value with the third count value to calculate the second error value (S 220 ), and comparing the second error value with the predetermined first threshold value (S 230 ). In this connection, the first threshold value is a value set by a user in order to determine whether how close the corrected oscillating frequency f 1  matches the frequency f 2  of the reference signal. 
         [0053]    Accordingly, if the second error value is smaller than the first threshold value, the correction success code and the setting value are stored in the memory  130  (S 240 ), and the correction completion signal is output (S 250 ). On the contrary, if the second error value is larger than the first threshold value, a re-correcting is performed to retry the correction of the oscillating frequency f 1  of the target signal. This is for providing precise oscillating frequency f 1  by way of comparing the second error value based on the oscillating frequency f 1  of the corrected target signal and the frequency f 2  of the reference signal with the predetermined first threshold value to retry the correction of the oscillating frequency f 1 . 
         [0054]    The re-correcting includes comparing the correction number with a predetermined second threshold value (S 260 ). In this regard, the correction number refers to the number that the oscillating frequency f 1  of the target signal is corrected, starting from zero. Additionally, the second threshold value is set in order to prevent the correction of the oscillating frequency f 1  of the target signal from being repeated endlessly with the value set by a user. Accordingly, if the correction number is larger than the second threshold value, the correction failure code is stored in the memory  130  (S 270 ), and the correction completion signal is generated (S 280 ). If the correction number is smaller than the second threshold value, the correction number is incremented by one (S 290 ), and it returns to the counting of the oscillating frequency f 1  of the target signal (S 120 ) to perform the correction of the oscillating frequency f 1  again. 
         [0055]    As shown in  FIG. 7 , the normal mode is performed if the start signal is not detected after the detecting of the start signal, so that the oscillating frequency f 1  of the target signal is measured (S 300 ), and then the setting value stored in the memory  130  is detected (S 310 ). Subsequently, the stored setting value is transmitted from the main processor  120  to the oscillator  10 , so that the oscillating frequency f 1  of the target signal is corrected so as to match the frequency f 2  of the reference signal (S 320 ). Therefore, even without the frequency f 2  of the external reference signal, the oscillating frequency f 1  of the target signal can be corrected by using the stored setting value. 
         [0056]      FIG. 8  is a diagram showing timings in the correction mode. Upon applying a start signal, the oscillating frequency f 1  of the target signal is measured, and the first counter  111  counts the oscillating frequency f 1  of the target signal. The reference signal is input simultaneously with this, the second counter  112  counts the frequency f 2  of the reference signal. When the second counter  112  reaches the reference time point, the comparator  113  calculates the first error value, and then a correction value is selected from the look-up table  121 . Subsequently, the main processor  120  computes a setting value to correct the oscillating frequency f 1 . Then, the oscillating frequency f 1  of the corrected target signal and the frequency f 2  of the reference signal are counted. After comparing two count values to calculate the second error value, the setting value is stored in the memory  130  if the second error value is smaller than the predetermined first threshold value, and an end signal is output. 
         [0057]    According to an exemplary embodiment of the present disclosure, errors in the oscillating frequency f 1  of the target signal caused by variations in processes are corrected automatically. Therefore, a process of measuring the oscillating frequency f 1  of the target signal for an individual integrated circuit to calculate a correction coefficient and store it can be eliminated. As a result, the correction processes become simpler and thus it takes less time to perform the correction processes. Additionally, variations in an operation frequency of an integrated circuit become smaller, so the yield of the integrated circuit is improved. As a result, reliability of the oscillator  10  is also improved. 
         [0058]    Although the embodiments of the present disclosure have been disclosed for illustrative purposes, it will be appreciated that the present disclosure is not limited thereto, and those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the disclosure. 
         [0059]    Accordingly, any and all modifications, variations or equivalent arrangements should be considered to be within the scope of the disclosure, and the detailed scope of the disclosure will be disclosed by the accompanying claims.