KR940011021B1 - Digital frequency demodulation method - Google Patents

Abstract

In a device for demodulating digital data whose frequency is modulated by using a predetermined look-up table, a digital frequency demodulating device includes: a data dividing part for receiving data whose frequency is modulated and then dividing it into a sine wave amplifying data value and a co-sine wave amplifying data for a same phase; an logic calculation processing unit for generating a plurality of binary signal by receiving the amplifying data from the data dividing part and then making data corresponding to the ratio of absolute values of the two type amplifying data; a look-up table for outputting phase data in response to the data generated from the logic calculation processing unit; an amending part for amending the output of the look-up table; a data-differential part for outputting the amended data and then feed-forwarding the next data input in the form of minus calculation; and data detecting part for detecting digital data corresponding to an information signal from the output data of the data-differential part.

Description

Digital frequency demodulation method and device

1 is a block diagram of a general digital frequency modulation device.

2 is a sine look-up table of a digital frequency modulator.

3 is a conventional digital frequency demodulation device.

4 is a block diagram showing an embodiment of a digital frequency demodulation device according to the present invention.

5 is a partial detailed view showing a comparison processing unit according to an embodiment of the present invention.

6 is an arc tangent lookup table according to an embodiment of the present invention.

7 is the tangent and arc tangent mixing table.

* Explanation of symbols for main parts of the drawings

20: data division 21, 33: time delay

22: π / 2 phase shifter 23: arithmetic processing unit

24: comparison processing unit 25, 37: divider

26, 27: code detector 28: comparator

29: switching unit 30: ROM (ROM)

31 correction unit 31 differential

34, 36: subtractor 35: data detector

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital frequency demodulation method and apparatus thereof, and more particularly, to a digital frequency demodulation method and apparatus for frequency demodulation of digitally modulated digital data using a look-up table.

In order to demodulate an input digital video signal and to demodulate the input video signal from the modulated and recorded data, a digital frequency modulation and demodulation device is generally used.

In general, in the case of frequency modulation, the general formula of the carrier is as follows.

Where Ac is a constant amplitude, f _c is a carrier frequency, K _f is a frequency sensitivity coefficient, and f (t) represents a modulated signal corresponding to an image signal. In the formula (1), when time t is expressed in the form of sampling time interval T, t = nT (n is an integer), and Equation (1) is as shown in Equation (2).

Where n is an integer and f _s is a sampling frequency or clock frequency. If defined as, the above formula (2) becomes the following formula (3).

Y _FM (nT) = AcSinAn... … … … … … … … (3)

here,

K ₁ is Frequency Deviation Factor and K ₂ is Carrier Frequency Factor.

The present invention relates to the implementation of equation (3) and will be described below in relation to equation (3).

1 and 2 show a conventional digital frequency modulation device and a sine check table of the modulation device according to the above-described theory. As the digital data f (nT) passing through the input terminal passes through the multiplier (1), the frequency shift is multiplied by the related constant K ₁ , and in the adder (2), the carrier frequency related constant K ₂ is added. The digital data passing through the adder 4 of the integrator 3 is outputted, and the data is fed back to the time delayer 5 and the process of adding the data to the next data in the adder 4 is repeated. Output digital data Is assigned to the address value of the ROM 6 in which the sign check table having the address size of 2y and the data size of 2 · 2x shown in FIG. Where x and y are constants that determine the amount of data to be processed in the lookup table. In addition, frequency-modulated digital data output from the ROM 6 as a data value (Y = AcSinAn) is recorded on a recording medium such as a video tape.

Since the digital frequency demodulator uses a function of tangent or cotangent, the amplitude component of the carrier has no meaning, so the amplitude component Ac is omitted.

3 is a conventional digital frequency demodulation device. When digital data (Y = Sin An) frequency-modulated by the above-described frequency modulation device is input through an input terminal of the digital frequency demodulation device, the amplitude of the sine wave in the delay unit 11 is shown. While the input data corresponding to (Y = Sin An) is delayed, the data input to the π / 2 phase shifter 12 corresponds to a waveform shifted by π / 2 with respect to the same phase, that is, the amplitude of the cosine wave. It is transformed into digital data (X = Cos An), and the amplitude data value of the sine wave and the cosine wave are applied to the same phase generated by the divider 13. The amplitude ratio (Y / X = TanAn) of the sine wave and the cosine wave to the same phase generated by the divider 13 is a corresponding phase value (An = Tan ⁻ ) in the ROM 14 in which an arc tangent lookup table is implemented. ^The output is transformed to ¹ ((Y / N)), and the reverse sequence of the processes performed between the input terminals of the digital frequency modulator of FIG. 1 and the integrator 3 is performed to reverse the frequency-modulated digital data f (nT). ) Is demodulated.

In the conventional digital frequency demodulation device as described above, since the data in the positive and negative regions corresponding to the amplitude band of the sine wave is needed in the ROM 14 in which the arc tangent lookup table is implemented, Its efficiency is rather low and requires a somewhat larger memory capacity. In addition, as the sampling interval of the modulated signal increases, the memory capacity thereof increases correspondingly, and therefore, in the case of a digital frequency demodulation device requiring a small sampling interval, improvement of inefficient memory operation is required.

An object of the present invention for solving the above problems is to transform the input digital data to fit the arc tangent irradiation table of the size π / 4, and also by using the symmetry of the tangent function and the cotangent function of the output data of the irradiation table The present invention provides a digital frequency demodulation method and apparatus capable of greatly reducing the capacity of a ROM having an arc tangent lookup table by the correction method.

A feature of the present invention for achieving the above object is a digital frequency demodulation device for demodulating frequency-modulated digital data using a predetermined look-up table. And a plurality of binary signals generated by receiving a data divider that separates the amplitude data of the sine wave amplitude data into the cosine waveform amplitude data, and the sine wave amplitude data and the cosine wave amplitude data generated by the data divider to generate a plurality of binary signals. An arithmetic processing unit for generating data corresponding to a ratio of the absolute value of the amplitude data to the absolute value of the cosine waveform amplitude data, a lookup table for outputting phase data corresponding to the data generated by the arithmetic processing unit, and the arithmetic operation; A correction unit for correcting the output value of the irradiation table by using the binary signal of the processing unit, and the correction unit A data differential part for outputting predetermined data, time-delaying the data, and subtracting the data immediately inputted thereafter, and a data detection part for detecting digital data corresponding to the information signal from the output data of the data differential part. Digital frequency demodulator.

According to another aspect of the present invention, a digital frequency demodulation method for demodulating digital data modulated using a predetermined look-up table includes inputting frequency-modulated data and amplitude data of a sine wave for the same phase. Dividing the amplitude data of the cosine waveform by the amplitude data of the cosine waveform and the amplitude data of the sinusoidal waveform and the cosine waveform generated in the dividing step to generate a plurality of binary control signals, and to generate a ratio of the absolute values of the amplitude data. A step of correcting the phase data using a binary processing signal of the arithmetic processing step; outputting the data corrected in the correcting step and time delaying the data immediately after A separation step of feeding forward in the form of subtracting the input data and the output data of the separation step. In the digital frequency demodulation comprises the step of detecting the digital data corresponding to the signal.

Hereinafter, a preferred embodiment of a digital frequency demodulation device according to the present invention will be described in detail with reference to the accompanying drawings.

4 is a block diagram showing an embodiment of a digital frequency demodulation device according to the present invention, wherein the digital frequency demodulation device includes a first time delay 21 and a π / 2 phase shifter 22 connected in parallel. A data divider 20, a comparison processor 24 for processing the input digital data to generate a control signal, and a first divider 25 for outputting the digital data corresponding to the amplitude ratio of the two input amplitude data. The calculation processing unit 23, the ROM 30 having the relation between the input data and the output data, and the correction unit 31 correcting the input data using the periodic symmetry of the tangent and the cotangent, and the second time delay unit ( 3) and a derivative 32 with a first subtractor 34 and a data detector 35 with a second subtractor 36 and a second divider 37.

5 is a detailed block diagram of the comparison processor 24 of FIG. The comparison processor 24 receives the digital data corresponding to the amplitude of the sine wave and outputs an absolute value and a binary signal of low (L) or high (H), and a first code detector 26. And a second code detector 27 that receives digital data corresponding to the amplitude of the cosine waveform and outputs an absolute value and a binary signal of L or H, and compares the data output from the code detectors 26 and 27 with size. The comparator 28 for generating a binary signal H or L, and the switching unit 29 for switching the digital data input from the code detectors 26 and 27 to two terminals under control of the output signal of the comparator 28. It is composed of

6 is an arc tangent irradiation table of a digital frequency demodulation device according to the present invention, which has a digital address value corresponding to an amplitude of 2x magnitude and a digital data value of size 1/8 · 2y corresponding to a phase of π / 4 size. . Here, x and y are constants equal to the data capacity determination constant of the above-described sine check table.

7 is a mixed irradiation table of arc tangent and arc cotangent to aid the understanding of the ROM 30 and the correction unit 31, which is a feature of the present invention.

In the embodiment of Fig. 4, the digital amplitude data (Y = SinAn) corresponding to the phase of the sine wave at regular time intervals is input to the data dividing unit 20 through the input terminal. The data inputted to the data divider 20 is outputted by the π / 2 phase shifter 22 as amplitude data (X = CosAn) corresponding to the cosine waveform in which the amplitude data (Y = SinAn) is phase shifted by π / 2. In the first retarder 21, the digital amplitude data (Y = SinAn) is delayed by a time corresponding to π / 2 phase shift and outputted in a form synchronized with the cosine data. The sine waveform amplitude data and the cosine waveform amplitude data inputted to the comparison processing section 24 of the calculation processing section 23 are processed by the code detectors 26 and 27, respectively, to obtain the absolute values | Y | and | X | output as c That is, d = H if SinAn≥0, d = L if SinAn <0, c = H if CosAn≥0, and c = L if CosAn <0, and the sign of each amplitude data is sent to the correction unit 31. . In addition, the amplitude data | Y | of the sinusoidal waveforms output from the sign detectors 26 and 27 and the amplitude data | X | of the cosine waveform are compared in magnitude in the comparator 28, and "H" or " The signal e of L "is transmitted to the correction part 31 and the switching thread | variety 29.

That is, in the case of | SinAn | ≥│CosAn |, it is transmitted in the form of H, and in the case of | SinAn | <│CosAn |. The output signal of the comparator 28 inputted to the switching unit 29 switches the switch in the switching unit 29. When the output signal of the comparator 28 is "H", the a terminal is a digital amplitude data of the cosine wave. When the b terminal is the digital amplitude data of the sine wave and Y is output, and the comparator 28 output signal is "L", the a terminal is the digital amplitude data of the sine wave | Y | is the cosine wave as the b terminal. Digital amplitude data of X | The amplitude data output from the comparison processing section 24 to the two terminals a and b is output from the first divider 25 in the amplitude of Tan An or Cot An. That is, digital data corresponding to the amplitude ratio of the sine wave and the cosine wave is output. The amplitude data of the tangent wave (│Y│ / │X│ = TanAn) or the cotangent wave amplitude data (│X│ / │Y│ = CotAn) is embodied in the ROM (30). When input to the arc tangent lookup table having an input address and output data of size 1/8 · 2y, the input data is assigned to the address value corresponding to the amplitude of FIG. 6 and output as the phase data value corresponding to the address value. . The digital data output as the data value 1 corresponding to the phase of the tangent wave or the cotangent wave in the arc tangent irradiation table ROM 30 is varied according to the output signals e, d, and c of the operation processor 23, and is corrected by the correction unit 31. ) Is output as the corrected data Q in the form of the corresponding correction equation shown in the correction table of Table 1 below.

TABLE 1

For example, the output data value 1 = 4 of the arc tangent irradiation table ROM 30, the output e of the comparator 28 of the arithmetic processing unit 23 is " L ", and the outputs d and c of the code detectors 26, 27 are In the case of "L " and " L ", respectively, Q = 1/2 · 2y + 4 is obtained by the correction equation Q = 1/2 · 2y + 1.

Data Q corrected and output by the correction unit 31 is input to the differential unit 32 by one terminal. While the delay time is delayed by the sampling time interval T in the delay unit 33 of the derivative unit 32, the same data input to the other terminal is output to the data detection unit 35. Data input to one terminal Reaches the first subtractor 34 without time delay, the time delayed data in the second delayer 33 Subtracts the above input data. Data (K ₂ + K ₁ f (nT)) corresponding to the difference of the continuous input data generated by the subtraction is input to the data detector 35. The data input to the data detector is input by the second subtractor 36. The carrier frequency related constant K ₂ is subtracted, and the second divider 37 divides the frequency pieces so that the related constant K ₁ disappears so that the output data of the data detector 35 is in the form of f (nT). The modulated information signal is demodulated and output.

In the above embodiment, the present invention is implemented using an arc tangent-type irradiation table using a tangent function, but the present invention may be implemented by constructing an irradiation table with arc tangent using cotangent. In the present invention, the sine wave input digital data is described as an embodiment, but it is also possible to implement within the scope of the present invention even when the cosine waveform digital data is input.

As described above, the digital frequency demodulation device according to the present invention has the effect of reducing the capacity of the ROM used as the lookup table.

Claims (19)

A digital frequency demodulation device for demodulating frequency-modulated digital data using a predetermined look-up table, comprising: receiving a frequency-modulated data and amplitude of a sine waveform and an amplitude of a cosine waveform for the same phase A data dividing unit for separating the data; Generates a plurality of binary signals by receiving the sinusoidal amplitude data and the cosine waveform amplitude data generated by the data divider, and corresponds to the ratio of the absolute value of the absolute value of the sinusoidal amplitude data and the cosine waveform amplitude data. An arithmetic processing unit for generating data; A lookup table for outputting phase data corresponding to the data generated by the calculation processing unit; A correction unit for correcting an output value of the irradiation table by using the binary signal of the calculation processing unit; A data differential unit for outputting the data corrected by the correction unit, feed-forwarding the subtracted data by time delaying the data; And a data detector for detecting the digital data corresponding to the information signal from the output data of the data differential part. The apparatus of claim 1, wherein the data division unit comprises: a delay unit for time-delaying and outputting the input amplitude data; And a? / 2 phase shifter for outputting amplitude data when the phase of the input data is shifted by? / 2. 2. The apparatus of claim 1, wherein the arithmetic processing unit comprises: a first code detector for outputting a binary signal corresponding to a positive / negative sign from the data division unit and a absolute value of the sinusoidal amplitude data in a sinusoidal amplitude data; A second code detector for outputting a binary signal corresponding to a positive / negative sign and an absolute value of the cosine waveform amplitude data from the cosine waveform amplitude data output from the data dividing unit; A comparator for magnitude comparing absolute values of amplitude data output from the code detectors and outputting a binary signal corresponding to the magnitude comparison; A switching unit for switching the absolute values of the amplitude data output from the first code detector and the second code detector to two terminals by using the binary signal output from the comparator; And a divider for dividing the data output from the two terminals of the switch, the divisor one being the divisor. The arctangent form of the π / 4 phase range according to claim 1, wherein the irradiation table has a data value of 1/8 · 2y size at a 2x size address value for constants x and y determined by the capacity of the irradiation table. Digital frequency demodulation device, characterized in that. The method of claim 1, wherein the corrector selects one of a tangent waveform and a cotangent waveform using a comparator output of the calculation processor, and uses a binary signal corresponding to a positive / negative sign of an amplitude with respect to a sine waveform of the calculation processor. Selects the phase region of the sine wave, selects the phase region of the cosine wave using a binary signal corresponding to the positive / negative sign of the amplitude of the cosine waveform, and compares the magnitude, sine wave, and cosine wave Digital frequency demodulation characterized in that the output value of the irradiation table is assigned to a phase value in the 2π range using a correction equation using the symmetry of the tangent waveform and the cotangent waveform within the phase range determined by the binary signal corresponding to Device. A digital frequency demodulation method for demodulating digital data modulated using a predetermined look-up table, wherein the frequency-modulated data is input and divided into amplitude data of a sine wave and amplitude data of a cosine waveform for the same phase. Doing steps; An arithmetic processing step of processing a sine waveform amplitude data and a cosine waveform amplitude data generated in the dividing step to generate a plurality of binary control signals, and outputting phase data corresponding to a ratio of absolute values of the amplitude data; ; Correcting phase data by using the binary control signal of the calculation processing step; A separation step of outputting the data corrected in the correction step, time-delaying the data to feed forward the subtracted data immediately; And detecting the digital data corresponding to the information signal from the output data of the separation step. The method of claim 6, wherein the data dividing step comprises: a delay step of time-delaying and outputting the input amplitude data; And outputting an amplitude data value when the phase of the input data is shifted by [pi] / 2. The method of claim 6, wherein the operation processing step comprises: a comparison processing step of comparing the output data of the data division step to output a plurality of binary control signals, absolute values of sinusoidal amplitude data and absolute values of cosine waveform amplitude data; Dividing the absolute values output in the comparison processing step; And a conversion step of converting the output data of the division step into phase data. 9. The method of claim 8, wherein the comparing step comprises: detecting a binary control signal corresponding to a negative / positive sign for each of sine wave data and cosine wave data in the output data of the data dividing step; Outputting an absolute value of the output data; Generating a binary control signal by comparing magnitudes of absolute values of absolute value data output in the code detection step; And converting and outputting the absolute value data of the amplitude output in the code detection step using the signal generated in the comparison step. 9. The arc tangent lookup table of claim 8, wherein the converting step is a π / 4 phase range having a data value of 1/8 · 2y at a 2x size address for constants x and y determined by the capacity of the lookup table. Digital frequency demodulation method characterized in that using. 7. The method of claim 6, wherein the correcting step comprises: selecting one of a tangent waveform and a cotangent waveform using a binary control signal output in the comparison processing step; Selecting a phase region of a sine wave by using a binary control signal corresponding to a sign of an amplitude with respect to a sine wave in the comparison processing step; Selecting a phase region of the cosine wave using a binary control signal corresponding to the sign of the amplitude of the cosine waveform; Assigning an output value of the calculation step to a phase value in the 2π range by using a correction equation using the symmetry of the tangent waveform and the cotangent waveform within the phase range determined by the binary control signal of the calculation processing step. Digital frequency demodulation method characterized by. 12. The correction equation is used when the control signal of the arithmetic processing step is a signal in which the absolute value of the sinusoidal amplitude is smaller than the absolute value of the cosine wave amplitude and the sign of the sinusoid and cosine waveform is positive (puls). Digital frequency demodulation method characterized in that the same. Q = 1 Where 1 is the output value of the conversion step and Q is the output value of the correction step. 12. The correction equation according to claim 11, wherein the control signal of the arithmetic processing step is a signal in which the absolute value of the sinusoidal amplitude is smaller than the absolute value of the cosine wave amplitude and the sinusoidal signal is a positive sign cosine waveform is a negative sign. Digital frequency demodulation method characterized in that the same. Q = 1/2, 2y-1 Where 1 is an output value of the conversion step, Q is an output value of the correction step, and y is a size range determination constant of the input data of the correction step. 12. The digital equation according to claim 11, wherein the control signal in the arithmetic processing step is a signal whose absolute value of the sine wave amplitude is smaller than the absolute value of the cosine wave amplitude and the sine wave is a negative sign. Frequency demodulation method. Q = 2y-1 Where 1 is an output value of the conversion step, Q is an output value of the correction step, and y is a size range determination constant of the input data of the correction step. The correction equation is as follows when the control signal of the arithmetic processing step is a signal in which the absolute value of the sinusoidal amplitude is smaller than the absolute value of the cosine wave amplitude and the sinusoidal and cosine waveforms are negative signs. Digital frequency demodulation method. Q = 1/2, 2y + 1 Where 1 is an output value of the conversion step, Q is an output value of the correction step, and y is a size range determination constant of the input data of the correction step. 12. The correction equation according to claim 11, wherein the control signal in the arithmetic processing step is a signal whose absolute value of the sinusoidal amplitude is greater than the absolute value of the cosine wave amplitude and the sinusoidal and cosine waveforms are positive. Digital frequency demodulation method. Q = 1/4, 2y-1 Where 1 is an output value of the conversion step, Q is an output value of the correction step, and y is a size range determination constant of the input data of the correction step. 12. The correction equation according to claim 11, wherein the control signal of the arithmetic processing step is a signal whose absolute value of the sinusoidal amplitude is greater than the absolute value of the cosine wave amplitude and the sinusoidal signal is a positive sign cosine waveform is a negative sign. Digital frequency demodulation method characterized in that the same. Q = 1/4, 2y + 1 Where 1 is an output value of the conversion step, Q is an output value of the correction step, and y is a size range determination constant of the input data of the correction step. 12. The correction equation according to claim 11, wherein the control signal of the arithmetic processing step is a signal whose absolute value of the sinusoidal amplitude is greater than the absolute value of the cosine wave amplitude and the sinusoidal signal is a negative sign cosine waveform is a positive sign. Digital frequency demodulation method characterized in that the same. Q = 3/4 · 2y + 1 Where 1 is an output value of the conversion step, Q is an output value of the correction step, and y is a size range determination constant of the input data of the correction step. 12. The correction equation is as follows when the control signal of the operation processing step is a signal whose absolute value of the sinusoidal amplitude is greater than the absolute value of the cosine wave amplitude and the sinusoidal and cosine waveform are negative signs. Digital frequency demodulation method. Q = 3/4 · 2y-1 Where 1 is an output value of the conversion step, Q is an output value of the correction step, and y is a size range determination constant of the input data of the correction step.