KR20000045608A - Sine/cosine look up device of phase tracking loop - Google Patents

Abstract

PURPOSE: A sine/cosine look up device of phase tracking loop is provided to easily embody hardware by embodying phase tracking loop without using memory. CONSTITUTION: A sine/cosine look up device of phase tracking loop includes a time delay buffer(21) producing sine value after delaying inputted phase accumulated in a phase accumulation table(8). An absolute value operation table(22) takes an absolute value from inputted phase accumulated in a phase accumulation table(8). A shift operation table(23) shift operates data produced form the absolute value operation table(22). A addition table(24) produces a cosine value by adding the values from the absolute value operation table(22) and the shift operation table(23).

Description

Sine / Cosine Lookup Device for Phase Tracking Loops

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase tracking loop (PTL) of HDTV (High Definition TeleVision, High Definition Television). Particularly, the sine of a phase tracking loop that facilitates hardware implementation by implementing a phase tracking loop without using a memory. It relates to a cosine lookup device.

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 FIR 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 multiplexer (5) for complex multiplexing the I and Q signals outputted from the delay unit (3) and the FIR filter (4); An error determiner (6) for receiving a complex multiplexed I, Q channel signal from the complex multiplexer (5) to determine an error and output a gain error and a phase error; A limit accumulator (7) which receives a gain error output from the error determiner (6), accumulates a 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 errors output from the error determiner (6); A sine / cosine lookup unit 9 is configured to receive the accumulated phases from the phase accumulator 8, compensate and store sine and cosine values of the phases, and output the compensating sine and cosine values to the complex multiplexer 5.

Thus, the channel equalizer located before the phase tracking loop operates on incoming I channel signals at a rate of 10.76 Msymbol / sec, and the 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 the FIR 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 output of the FIR filter 4 which is a linear filter is compensated for by the complex multiplexer 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 sine / cosine look up table (LUT) 9 via the phase accumulator 8.

2 is a block diagram of a sine / cosine lookup apparatus of a conventional phase tracking loop.

Thus, the conventional sine / cosine lookup unit 9 implements the sine memory 13 and the cosine memory 14 using a ROM. In the case of implementing the sine / cosine lookup section 9 in ROM, assuming that the number of input bits of the ROM is n, the number of addresses is 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 memory 13 and the cosine memory 14 to output a sine / cosine value corresponding to the address.

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

Where n is the address input of the sine / cosine lookup section 9, N is the number of data in the sine / cosine lookup section 9, sin (n) is the magnitude of the sine and cos (n) is the magnitude of the cosine .

However, the conventional apparatus has a disadvantage in that the size of the memory varies greatly according to the number of bits input to the sine / cosine memories 13 and 14.

Accordingly, the present invention has been proposed to solve the above-mentioned conventional problems, and an object of the present invention is to implement a phase tracking loop without using a memory, and to perform hardware sine / cosine of a phase tracking loop. It is to provide a lookup device.

In order to achieve the above object, a sine / cosine lookup device of a phase tracking loop according to the present invention,

A delay unit for receiving the delayed phase from the phase accumulator and outputting a sine value; An absolute value calculator which receives the accumulated phase from the phase accumulator and takes an absolute value of the phase; A shift calculator which shifts the data output from the absolute value calculator; The technical configuration is characterized by the addition unit for outputting the cosine value by adding the output of the absolute value operation unit and the shift operation unit.

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

2 is a block diagram of a sine / cosine lookup device of a conventional phase tracking loop;

3 is a block diagram of a sine / cosine lookup apparatus for a phase tracking loop according to the present invention.

<Explanation of symbols for main parts of drawing>

8: phase accumulator 9: sine / cosine lookup unit

11: adder 12: accumulator

21: delay unit 22: absolute value calculator

23: shift calculator 24: adder

Hereinafter, with reference to the accompanying drawings an embodiment according to the technical idea of the sine / cosine look-up device of the phase tracking loop of the present invention as described above in detail.

3 is a block diagram of a sine / cosine lookup apparatus for a phase tracking loop according to the present invention.

As shown therein, a delay unit 21 for receiving and delaying a phase accumulated in the phase accumulator 8 and outputting a sine value; An absolute value calculator 22 which receives the accumulated phase from the phase accumulator 8 and takes an absolute value of the phase; A shift calculation unit (23) which shifts the data output from the absolute value calculation unit (22); And an adder 24 for outputting a cosine value by adding the outputs of the absolute value calculator 22 and the shift operator 23.

Referring to the operation of the present invention configured as described above is as follows.

First, the present invention develops a sine / cosine function into a Taylor series and approximates it to a linear function in order to remove the hardware burden on the memory size which increases exponentially with the increase in the number of address input bits. The sine / cosine lookup unit 9 is implemented by eliminating the burden on and using an absolute value calculator, a shift operator, and an adder.

Expanding the sine / cosine function to the Taylor series is the same as Equations 3 and 4 below.

In Equation 3 and 4 θ Assuming that is a small value, Equations 3 and 4 are the following Equations 5 and 6, respectively.

sin (θ) ≈θ

In this way, it is possible to approximate a linear function as in Equations 5 and 6.

From this, it can be seen that the sine / cosine lookup unit 9 can be implemented using only an absolute value calculator, a shift operator, and an adder.

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 sine / cosine lookup device of the phase tracking loop according to the present invention has an effect of facilitating hardware implementation by implementing the phase tracking loop without using a memory.

Claims (1)

A sine / cosine lookup device of a phase tracking loop, wherein the sine / cosine lookup device includes: A delay unit for receiving the delayed phase from the phase accumulator and outputting a sine value; An absolute value calculator which receives the accumulated phase from the phase accumulator and takes an absolute value of the phase; A shift calculator which shifts the data output from the absolute value calculator; And an adder configured to output a cosine value by adding the output of the absolute value calculator and the shift calculator to output a cosine value.