Table lookup optimization method and numerical controlled oscillator

Abstract

The invention aims to provide a table lookup optimization method, which comprises the following steps of: a, representing numerical controlled oscillator (NCO) forms corresponding to different television audio carrier frequencies by using a reference form; b, shortening and optimizing the reference form to a 1 / 4 length, and obtaining other non-reference forms from the reference form; and c, further optimizing and storing the reference form according to sine regularities to obtain a sine value and a cosine value by once addressing. The invention also provides a numerical controlled oscillator utilizing the table lookup optimization method, which comprises a form unit, a counting unit, an addressing unit, a splitting unit and a multiplication unit, wherein the form unit is set in a read-only memory (ROM), and stores NCO form data optimized by the table lookup optimization method; the counting unit counts the input television audio carrier frequencies, and takes a count as an index value; the addressing unit addresses the form unit to obtain required NCO form data; the splitting unit splits the required NCO form data into the sine value and the cosine value; and the multiplication unit receives the sine value and the cosine value, and multiplies the sine value and the cosine value by the input television audio carrier frequencies respectively.

Description

technical field [0001] The invention relates to a numerically controlled oscillator, in particular to a table look-up optimization method and a digitally controlled oscillator utilizing the table look-up optimization method. Background technique [0002] The audio signals received at the receiving end of the analog TV tuner, including FM, NICAM and other audio signals, need to be demodulated before the final digital decoding can be completed. In order to satisfy the subsequent digital decoding, NCO (Numerical controlled oscillator, digitally controlled oscillator) can be used to satisfy the demodulation of different signals. The NCO performs the multiplication between the signal and the complex sine, and realizes the function of converting one frequency into another frequency. Sampling samples of sine values ​​are stored in a look-up table, and the look-up table is stored in a memory, such as a traditional RAM (random access memory () or ROM (read-only memory). At present, ...

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Problems solved by technology

However, since the accuracy achieved by this method is related to the degree of approximation, in order to improve the accuracy, it is necessary to increase the storage capacity and hardware overhead of the NCO table

In addition, there is also a general-purpose NCO table made according to the minimum step value of the signal. Although this NCO table is highly versatile, its efficiency is too low for chips that need to be used in real-time decoding to meet practical applications.

[0003] For the shortcomings of the above method, in order to obtain the accurate value of the corresponding carrier frequency, there is also a specific NCO table set by the NCO module according to the specific carrier frequency of the received signal, which corresponds to the carrier frequency one by one. Although this method is fast in the demodulation process , the cost is not high, but the limitation is great. Once the carrier frequency changes, this NCO form will become invalid

For the commonly used analog TV audio under different standards, there are 9 different carrier frequencies. If each system is designed with its own set of NCO tables, the amount of table data to be stored will be very large, resulting in the cost of the decoding chip. too high

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