JP2002009856A - Inverse tangent arithmetic circuit in digital signal processing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem such that the logarithm function ROM of J and K, a subtraction circuit obtaining the difference of the respective logarithms, an inverse logarithm function ROM and an inverse tangent function ROM are required for obtaining a phase component θ from orthogonal demodulation outputs J and K in a digital radio machine and that it is difficult to constitute the ROM by ROM loaded on one DSP since memory capacity comes short. SOLUTION: The outputs J and K of the phase range reduction part 31 of a demodulation part 3 are inputted to the inverse tangent function ROM 32. The inverse tangent function ROM 32 is the inverse tangent operation table of J/K, where J and K are set to be the addresses of an operation. The value of Tan-1J/K is directly outputted from the output.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an arc tangent operation circuit in digital signal processing, and more particularly, to an arc tangent operation table using an in-phase component and a quadrature component magnitude component of a quadrature demodulated output as an address to calculate a phase component of a demodulated output. The present invention relates to an arctangent operation circuit for performing an operation.

[0002]

2. Description of the Related Art In recent years, digital circuit technology has rapidly developed, and in the field of wireless communication, a technology of digitizing a received analog signal and selecting or modulating the channel by a digital signal processing technology has been actively used. I have. FIG. 3A is a schematic configuration diagram showing an example of a conventional demodulator of a digital radio. As shown in FIG. 1, the present demodulator comprises a quadrature demodulator 1 and an A / D converter 2
a, 2b, the phase range reduction unit 41 and the logarithmic function ROM (Re
ad Only Memory) 42a, 42b, a subtraction circuit 43, an antilogarithmic function ROM 44, an arctangent function ROM 45, and a demodulation unit 4 including a phase range expansion unit 46. In the figure, a quadrature demodulator 1 extracts an in-phase component and a quadrature component of a quadrature demodulated signal from a received signal whose frequency has been converted by a high-frequency receiving unit (not shown). The respective components are converted into digital signals in A / D converters 2a and 2b, respectively, and the digital in-phase component X and quadrature component Y are input to the demodulation unit 4.

The quadrature demodulated signals X and Y input to the phase range reduction section 41 of the demodulation section 4 are determined by the phase range reduction section 41 to be positive or negative and have respective magnitudes | X |
And | Y | are calculated and compared, and the smaller value is set to J and the larger value is set to K, and the logarithmic function ROM is used.
The signals are output to 42a and 42b. And the logarithmic function R
LogJ for OM42a, LogK for logarithmic ROM42b
Is calculated, and each value is output to the subtraction circuit 43, and the value of (LogJ−LogK) = LogJ / K is calculated. Next, in the antilogarithmic function ROM 44, ANTILog (LogJ /
K) = J / K is calculated and the result is the arctangent function ROM
Is output to 45, the phase theta = tan in inverse tangent function ROM 45 ^- is ¹ J / K obtained and outputted to the phase extension 56.

Since the value of the output J / K of the antilogarithmic function ROM 44 is 0 <(J / K) <1, the inverse tangent function RO
The output θ = tan ^{− 1} J / K of M45 is output as a value in the range of 0 <θ <45 °. Therefore, the arctangent function ROM
The output of 45 is the sign of X and Y sent from the phase range reduction unit 41 in the phase range expansion unit 46, | X |
The angle is corrected to 0 <θ <360 ° based on the information of the magnitude relationship of Y | and output as a demodulated output. The correction method is performed as follows according to the correction table shown in FIG. That is, in the first and second columns of the table, the positive and negative of X and Y,
The magnitude relationship between | X | and | Y | is selected in the third column, and the output θ of the inverse tangent function ROM 45 is corrected by the method specified in the fourth column. For example, let the output of the arctangent function ROM 45 be θ ₀ ,
When the input signals X and Y of the phase range reduction unit 41 are X> 0 and Y <
0, when there is a relation of | X | <| Y |
Output the corrected angle (180−θ ₀ ) degrees as the demodulated output.

[0005]

However, in order to realize the arithmetic processing for obtaining the divided value (J / K) of J and K by the above-described procedure, the logarithmic function ROMs 42a and 42b of J or K must be used. Many arithmetic processing units such as an antilogarithmic function ROM 44 and a subtraction circuit 43 are required. Further, as an apparatus, an arctangent function ROM 45 for obtaining the phase component θ is used.
Is required, and ROs mounted on one DSP (Digital Signal Processor) are equipped with several types of function ROMs.
Attempting to configure with only M is impossible with current DSPs because of insufficient storage capacity. Therefore, when the above-described arithmetic processing is performed by the ROM, a dedicated ROM needs to be prepared separately from the DSP, so that there has been a problem that the circuit configuration is complicated. For example, the division value obtained from the output of the antilogarithmic function ROM 44 is divided by digital signal processing to obtain a highly accurate result, which requires a complicated processing step, and thus requires a long time. What is required is well known. In addition, if a complicated process is replaced with a simple approximation formula in order to speed up the process, the expected accuracy cannot be obtained. Therefore, high-speed and high-precision calculation becomes difficult. Therefore, for example, as described above, in the conventional demodulation processing, X and Y of the digital quadrature demodulated signal are respectively reduced to values in the range of 0 to 45 °, and the obtained J,
By using a logarithmic function ROM which is relatively easy to realize from K (J <K), the values of the logarithms of J and K are obtained, and the inverse logarithm of the difference is obtained, thereby quickly dividing the values of J and K (J /
Means for determining K) have been taken. The present invention has been made to solve the above problems,
It is an object of the present invention to provide a demodulation device including an arithmetic processing circuit using a simple function ROM.

[0006]

According to a first aspect of the present invention, there is provided an arithmetic circuit for calculating an arc tangent of a division value of a two-input signal in digital signal processing. It is characterized in that an arc tangent value of a division value is directly obtained from the two input signals by a ROM (Read Only Memory) serving as an address of an operation table. In the invention of claim 2,
An arithmetic circuit for calculating a phase component of a demodulated output from an in-phase component and a magnitude component of a quadrature component of a quadrature demodulated output of a digital wireless device,
The magnitude components of the in-phase component and the quadrature component are respectively set as addresses of a two-dimensional array of the arctangent calculation table. According to a third aspect of the present invention, in the arctangent operation circuit of the second aspect, the array of the arctangent operation table is a one-dimensional array table.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on an embodiment shown in the drawings. FIG. 1A is a schematic configuration diagram showing an embodiment of a demodulator for a digital radio according to the present invention. As shown in the figure, the demodulation device includes a demodulation unit 3 including a quadrature demodulator 1, A / D converters 2a and 2b, a phase range reduction unit 31, an arctangent function ROM 32, and a phase range expansion unit 33. It is composed of The functions and operations of the quadrature demodulator 1, the A / D converters 2a and 2b, the phase range reduction unit 31 and the phase range expansion unit 33 are shown in FIG.
Since the functions and operations of the quadrature demodulator 1, the A / D converters 2a and 2b, the phase range reduction unit 41, and the phase range expansion unit 46 shown in (a) are the same, the following description is characteristic of the present invention. The description will focus on the function and operation of the arc tangent function ROM 32 having the configuration.

In FIG. 1A, a quadrature demodulator 1 extracts an in-phase component and a quadrature component of a quadrature demodulated signal from a received signal, and the components are A / D converters 2a and 2b, respectively.
Are converted into digital signals X and Y and output to the demodulation unit 3. The quadrature demodulation signals X and Y input to the phase range reduction section 31 of the demodulation section 3 are determined to be positive or negative by the phase range reduction section 31 and have respective magnitudes | X |
And | Y | are calculated and compared, and the smaller value is set to J and the larger value is set to K, and the arctangent function RO
Output to M32.

FIG. 1 (b) shows the inverse tangent function ROM 32.
This table is composed of X, Y
When the operation precision of is a two's complement and a 4-bit numerical value
3 shows a configuration of the OM. As shown in the figure, the operation table is formed in a two-dimensional manner, and the outputs θ and K of the phase range reduction unit 31 are used as the addresses of the operation table to obtain the phase θ.
= Tan ^{- 1} J / K, and θ (degrees) obtained from this table is output to the phase range extension unit 33. In the phase range extending section 33, the input phase signal θ is corrected to an angle of 0 <θ <360 ° according to the correction table of FIG.
Output as demodulated output.

FIG. 2 is a calculation table showing a modified embodiment of the arctangent function ROM 32 of the demodulator according to the present invention. The operation table in the arctangent function ROM 32 shown in FIG. 1B has a two-dimensional array configuration using J and K as addresses. As can be seen from the table in FIG. The area of the address J where J> K is a useless area, so that the RO
The M capacity becomes unnecessarily large. An operation table configured without such a defect is the table shown in FIG.
The configuration of the operation table in this ROM is such that only necessary element portions are sequentially extracted from the column of low K values in the operation table shown in FIG. 1B and arranged in a one-dimensional Z array. The relationship between inputs J and K and address Z is given by equation (1). Z = J−1 + K (K + 1) / 2 (1) According to the calculation table of this configuration, the arctangent function ROM 32
The required memory capacity is about half that of FIG. 1B, and the memory capacity of the device can be greatly reduced.

[0011]

As described above, according to the present invention,
The division operation, the logarithmic function, and the operation of the antilogarithmic function, which are conventionally required, are not required, and the signal processing amount can be reduced. For this reason, a great effect can be achieved in providing an excellent demodulator having a high speed and a high calculation accuracy.

[Brief description of the drawings]

FIG. 1A is a schematic configuration diagram showing an example of an embodiment of a demodulator for a digital wireless device according to the present invention, and FIG.
7A is an operation table configured in the inverse tangent function ROM of the demodulator of FIG.

FIG. 2 is a modified example of the operation table configured in the arctangent function ROM of FIG.

FIG. 3A is a schematic configuration diagram showing an example of a demodulator of a conventional digital radio, and FIG. 3B is a phase component correction table of an inverse tangent function ROM output.

[Explanation of symbols]

1 ... quadrature demodulator, 2a, 2b .. A /
D converter, 3... Demodulation unit according to the present invention, 4.
Conventional demodulation section, 31... Phase range reduction section, 3
2... Arctangent function ROM, 33..
41... Phase range reduction section, 42a, 42b.
Logarithmic function ROM, 43 subtraction circuit, 44 antilogarithmic function ROM, 45 tangent function ROM, 46
・ Phase range extension

Claims (3)

[Claims] 1. An arithmetic circuit for calculating an arc tangent of a division value of a two-input signal in digital signal processing, wherein the ROM (Re) uses the two-input signal as an address of an arc-tangent operation table.
an arc tangent calculation circuit, wherein an arc tangent value of a division value is directly obtained from the two input signals by an ad only memory. 2. An arithmetic circuit for obtaining a phase component of a demodulated output from a magnitude component of an in-phase component and a quadrature component of a quadrature demodulation output of a digital wireless device, wherein the magnitude component of the in-phase component and the magnitude component of the quadrature component are respectively inversed. 2. The arctangent operation circuit according to claim 1, wherein the address is a two-dimensional array address of the tangent operation table. 3. The arctangent calculation circuit according to claim 2, wherein the array of the arctangent calculation table is a one-dimensional array table.