KR20000045612A - Numerically controlled oscillator of phase tracing loop - Google Patents

Abstract

PURPOSE: A numerically controlled oscillator is provided to reduce the memory size by calculating a result value of the sine/cosine calculation process in advance and estimating a change range of a phase error near to 0 degree. CONSTITUTION: A sine lookup unit(20) inputs a phase accumulated in a phase accumulator(8), stores only sine values with respect to positive phases, determines the signs of the sign values according to the signs of the phases, and outputs the sign values. A cosine lookup unit(30) inputs a phase accumulated in the phase accumulator(8), reduces and then stores a bit width from a cosine value of the phase, restores the original cosine value, and outputs the restored cosine value. The sine lookup unit(20) includes a sign storage(21) for inputting the phase accumulated in the phase accumulator(8).

Description

Numerical Controlled Oscillator of Phase Tracking Loop

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a numerically controlled oscillator (NCO) of a phase tracking loop (PTL) of HDTV (High Definition TeleVision, High Definition Television), in particular the result of a sine / cosine calculation process of a numerically controlled oscillator. The present invention relates to a numerically controlled oscillation apparatus of a phase tracking loop which reduces a size of a memory by calculating a value in advance and storing the result in a memory and estimating a change range of a phase error close to 0 degrees.

In general, HDTV, such as the GA (Grand Alliance) standard, uses a phase tracking loop. The HDTV is a TV that realizes higher definition and larger screen size by doubling the number of scanning players and increasing the aspect ratio to 16: 9 (4: 3 for general television) compared to the general television.

In general HDTV, there is a phase tracking loop, which tracks the phase and gain error from the transmitted signal and compensates for the error, thereby accurately recovering the data in the subsequent decoder.

1 is a block diagram of a phase tracking loop of a general HDTV receiver.

As shown therein, an adder 1 for adding the output of the equalizer and the output of the multiplier 2; A multiplier (2) which multiplies the output of the equalizer by the value of the limit accumulator (7); A delay unit 3 for delaying the output of the adder 1 and outputting an in-phase I channel signal; A linear filter (4) for performing a finite impulse response (FIR) filtering on the output of the adder 1 to output a Q channel signal having a quadrature phase; A complex multiplier (5) for complex multiplying the I and Q signals output from the delay section (3) and the linear filter (4); An error discriminating unit (6) for receiving an I / Q channel signal multiplied by the complex multiplier (5) to determine an error and outputting a gain error and a phase error; A limit accumulator (7) which receives the gain error output from the error discriminator (6), accumulates the gain error measurement value, calculates an average thereof, and outputs the average value to the multiplier (2); A phase accumulator (8) for accumulating the phase error output from the error discriminator (6); It consists of a numerically controlled oscillator 9 which receives the accumulated phase from the phase accumulator 8, compensates for and stores the sine and cosine of the phase, and outputs it to the complex multiplier 5.

Thus, the channel equalizer located before the phase tracking loop operates on the input I channel signal at a rate of 10.76 Msymbol / sec, and the quantization output of the channel equalizer is input to the phase tracking loop.

The I channel signal input to the phase tracking loop is first gain adjusted and then passed through a linear filter 4 to produce an estimate of the Q channel signal. This is possible because the I and Q components of the VSB (Vestigial SideBand) modulated signal are in a linear transformation similar to the Hilbert transform. The complex signal consisting of the I channel signal input to the phase tracking loop and the Q channel signal which is the output of the FIR filter 4 which is the linear filter is compensated for by the complex multiplier 5.

The phase error and the gain error are calculated by the decision feedback method. The phase error thus calculated is input to the address value of the numerically controlled oscillator 9 which is a sine / cosine look up table (LUT) via the phase accumulator 8.

2 is a block diagram of a numerically controlled oscillation device of a conventional phase tracking loop.

Thus, the numerically controlled oscillator 9 implemented in the related art implements a sine ROM 13 and a cosine ROM 14 using a ROM. When the numerically controlled oscillator 9 is implemented in ROM, the number of input bits in the ROM is n. 2 ⁿ Becomes

The output of the adder 11 of the phase accumulator 8 is input to the accumulator 12 so that the phase error is accumulated in the phase accumulator 8. Then, the output of the accumulator 12 is input to the addresses of the sine rom 13 and the cosine rom 14, and outputs a sine / cosine value corresponding to the address to the complex multiplier 5.

The sine / cosine values at this time are as shown in Equations 1 and 2 below.

Where n is the address input of the numerically controlled oscillator 9, N is the number of data in the numerically controlled oscillator 9, sin (n) is the magnitude of the sine, and cos (n) is the magnitude of the cosine.

However, since the size of the memory varies according to the number of bits input to the sine / cosine ROM 13 and 14, the conventional apparatus has a disadvantage in that the memory capacity becomes very large.

Accordingly, the present invention has been proposed to solve the conventional problems as described above, and an object of the present invention is to calculate the result value of the sine / cosine calculation process of the numerically controlled oscillator in advance and store it in the memory, and the variation range of the phase error is It is to provide a numerically controlled oscillator of a phase tracking loop that can reduce the size of memory by estimating near zero degrees.

In order to achieve the above object, a numerically controlled oscillation device of a phase tracking loop according to the present invention,

A sine lookup unit which receives the accumulated phases from the phase accumulator and stores only the sine values for the positive phases, and then determines the sign of the sine values according to the sign of the phases and outputs the sine values; As a technical feature of the present invention, the phase accumulator comprises a cosine lookup unit which receives the accumulated phase and stores the bit-width from the cosine value of the phase, stores the bit-width, restores the original cosine value, and outputs the restored cosine value. do.

1 is a block diagram of a general phase tracking loop,

2 is a block diagram of a numerically controlled oscillation device in a conventional phase tracking loop.

3 is a block diagram of a numerically controlled oscillation device in a phase tracking loop according to the present invention.

<Explanation of symbols for main parts of drawing>

8: phase accumulator 9: numerically controlled oscillator

11: phase adder 12: accumulator

20: sign lookup unit 21: code storage unit

22: absolute value calculator 23: sine memory

24: inverter section 25: multiplexing section

30: cosine lookup unit 31: the first addition unit

32: cosine memory 33: second adder

Hereinafter, with reference to the accompanying drawings, an embodiment according to the technical idea of the numerically controlled oscillation apparatus of the present invention, the phase tracking loop as described above is as follows.

first

3 is a block diagram of a numerically controlled oscillation device in a phase tracking loop according to the present invention.

As shown in this figure, the sine lookup unit receives the accumulated phases from the phase accumulation unit 8 and stores only the sine values for the positive phases, and then determines the sign of the sine values according to the sign of the phases and outputs the sine values. 20; The cosine lookup unit 30 receives the accumulated phase from the phase accumulator 8 and stores the cosine value of the phase by reducing the bit-width, and then restores the original cosine value to output the restored cosine value. do.

The sine lookup unit 20 includes: a sign storage unit 21 which receives a phase accumulated by the phase accumulator 8 and stores only a sine value for a positive phase; An absolute value calculator 22 which receives the accumulated phase from the phase accumulator 8 and takes an absolute value of a sine of phase; A sign memory (23) for storing data output from the absolute value calculator (22); An inverter unit (24) for inverting the sign of the sine value stored in the sine memory (23); The multiplexer 25 receives the data of the sine memory 23 and the inverter unit 24, determines a sign according to a sign of a sine value stored in the sign storage unit 21, and outputs a multiplexed sine value. It consists of.

The cosine lookup unit 30 receives a phase accumulated by the phase accumulator 8 and subtracts a cosine value of a phase from a value 1 to reduce the bit-width from the cosine value of the phase. 31); A cosine memory 32 for storing data of the first adder 31; The second adder 33 is configured to restore the original cosine value by adding 1 to the cosine value of the phase of the cosine memory 32 and output the restored cosine value.

Referring to the operation of the present invention configured as described in detail as follows.

First, the phase tracking loop of the HDTV receiver estimates and compensates for the fine phase error present in the received signal. This compensation process can be represented by the following equations (3) and (4).

RealOutput I (n) = I '′ (n) cos (θ) -Q'′sin (θ)

ImaginaryOutput Q (n) = I '′ (n) sin (θ) + Q′′cos (θ)

here I '′ (n) Is the real value entered in phase, Q ′ ′ (n) Is the imaginary value of the input quadrature.

This process input complex signal I '′ (n) + jQ ′ ′ (n) Phase error correction signal cos (θ) + jsin (θ) And the result of complex multiplication. This correction signal is the phase error predicted by the phase tracking loop. θ It is generated through the process of sine and sine, and in actual implementation, the computational process puts a considerable hardware burden.

Therefore, in the present invention, the resultant value of the sine / cosine operation is calculated in advance and stored in a memory ROM (Read Only Memory). θ A look up table (LUT) method is used to output a stored value according to the value.

This LUT contains all the θ You can store the values corresponding to the input, but in this case, you need to consider how to implement them. The estimated phase error in the phase tracking rope used in the present invention θ Since the variation range of is estimated to be close to 0 degrees, this property can be used to reduce the size of the memory used in the LUT. The present invention stores sine / cosine values corresponding to 0-10 degrees.

In the case of the sine lookup unit 20, the positive sine of 0 θ Sine and negative for θ The sine values for are the same absolute value but have different signs. Therefore, using this property, the sine lookup unit 20 θ After storing only the sine value for in the sign storage unit 21 θ The output of the sine lookup unit 20, ie, the sign of the sine value, is input to the complex multiplier 5 according to the sign of.

The algorithm is summarized as follows.

sine LUT = abs (sin (theta))

IF theta 〈0 THEN

Complex Multiplier Imaginary Input = -sine LUT

ELSE

Complex Multiplier Imaginary Input = sine LUT

END IF;

Therefore, the existing negative number θ It is possible to reduce the size of the sine memory 23 by half than when storing the sine value for the value.

On the other hand, in the case of the cosine look-up unit 30, the positive sign according to the characteristics of the cosine function θ And negative θ Since it has the same value for, enter θ Can be shared regardless of the sign of θ Cosine LUT for Negative θ Share an operation on. And input θ Since the range is close to 0 degrees, the cosine values close to +1.0, which are relatively large as a result of the cosine operation, must be stored in the cosine lookup unit 30. This increases the bit-width for cosine values stored in cosine memory 32, thus increasing memory capacity. In order to reduce the bit-width, an operation as shown in Equation 5 below is performed by the first adder 31 and stored in the cosine memory 32.

Cosine LUT = 1-cos (θ)

in this case Cosine LUT Since values close to 0 are stored, they have a smaller bit-width than the conventional method, and thus also reduce the memory capacity of the cosine memory 32. The output value of the cosine memory 32 which has undergone such a calculation process is restored to the original cosine value by performing the calculation process as shown in Equation 6 in the second multiplier 33 and input to the complex multiplier 5.

Complex Μltiplier Real Input = 1 + cosine LUT

As described above, the present invention reduces the size of the memory by calculating the result value of the sine / cosine calculation process of the numerically controlled oscillator in advance and storing it in the memory and estimating the variation range of the phase error close to 0 degrees.

Although the preferred embodiment of the present invention has been described above, the present invention may use various changes, modifications, and equivalents. It is clear that the present invention can be applied in the same manner by appropriately modifying the above embodiments. Accordingly, the above description does not limit the scope of the invention as defined by the limitations of the following claims.

As described above, the numerically controlled oscillation device of the phase tracking loop according to the present invention calculates the result value of the sine / cosine calculation process of the numerically controlled oscillator in advance and stores it in the memory and estimates the variation range of the phase error close to 0 degrees. As a result, the size of the memory can be reduced.

Claims (3)

In the numerically controlled oscillation apparatus of a phase tracking loop, A sine lookup unit which receives the accumulated phases from the phase accumulator and stores only the sine values for the positive phases, and then determines the sign of the sine values according to the sign of the phases and outputs the sine values; A phase tracking loop comprising a cosine lookup unit for receiving the accumulated phase from the phase accumulator and reducing the bit-width from the cosine value of the phase, and then restoring the original cosine value to output the restored cosine value. Numerically controlled oscillation device. The method of claim 1, wherein the sign lookup unit, A code storage unit which receives a phase accumulated in the phase accumulator and stores only a sine value of a positive phase; An absolute value calculator which receives an accumulated phase from the phase accumulator and takes an absolute value of a sine of phase; A sign memory for storing data output from the absolute value calculator; An inverter unit for inverting a sign of a sine value stored in the sine memory; The oscillator of the phase tracking loop, comprising: a multiplexer configured to receive the data of the sine memory and the inverter and determine a sign according to the sign of the sine value stored in the sign storage unit, and to output the sine value. . The method of claim 1, wherein the cosine lookup portion, A first adder configured to receive the accumulated phase from the phase accumulator and subtract the cosine of the phase from a value of 1 to reduce the bit-width from the cosine of the phase; A cosine memory for storing data of the first adder; And a second adder configured to restore an original cosine value by adding 1 to a cosine value of a phase of the cosine memory, and output a reconstructed cosine value.