KR100599903B1 - Frequency modulated audio transmitter circuit using full-cmos and fabrication method thereof - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency modulated audio transmission integrated circuit using a complementary metal oxide semiconductor device and a method of controlling the same, comprising an audio block for inputting an audio signal, and generating and determining a frequency required for stereo modulation and FM carrier generation. An oscillation block and a frequency synthesis block, an FM modulation block for frequency-modulating a mixed signal, and a stereo modulation block for multi-step stereo modulation of an audio signal in at least three or more steps. This includes manufacturing process technology applied to circuits. The multi-stage weighted stereo multiplexing scheme is adopted in the stereo modulation section of the audio transmission integrated circuit to minimize the harmonic noise components that may be involved in the multiplexing and greatly improve the quality of the transmitted audio signal. By applying pure CMOS (complementary metal oxide semiconductor) technology to fabricate an audio transmission integrated circuit, it is possible to realize a small chip with low power driving, and the audio transmission chip according to the present invention can be effectively used in various portable terminals having battery power. That has the optimal advantage.

Audio, Transmission, Integrated Circuits, Multilevel, Weighted, Stereo, Multiplexing, CMOS, Frequency, Modulation, Multiplexing

Description

Frequency modulated audio transmitter integrated circuit using complementary metal oxide semiconductor device and its control method {Frequency modulated audio transmitter circuit using full-CMOS and fabrication method}

1 is a block diagram showing a frequency modulated audio transmission chip according to the prior art.

2 is a spectral simulation diagram of a typical sine wave

3 is a conventional square wave chopper signal

4 is a spectral simulation diagram of a conventional square wave

FIG. 5 is a block diagram illustrating a frequency modulated audio transmission integrated circuit using a complementary metal oxide semiconductor device using eight-stage weighted stereo multiplexing according to the present invention.

6 is a clock signal diagram for driving an eight-stage weighted stereo multiplex switch of the present invention;

7 is an eight-step weighted stereo multiplexing block diagram of the present invention.

8 is a conceptual diagram of a switch block for eight-stage weighted stereo multiplexing according to the present invention

9 is a sine wave and digital sine wave comparison diagram

10 is a comparison diagram between two-stage and eight-stage weighted stereo multiplexing

11 is a comparison diagram of two- and eight-stage weighted stereo multiplexed spectrum simulations.

The present invention relates to a method of designing and controlling a frequency-modulated audio transmission chip. More particularly, the entire circuit is implemented as a complementary metal-oxide semiconductor (CMOS) device, and a stereo multiplexer (MPX) is provided. The present invention relates to a frequency modulated audio transmission integrated circuit using a complementary metal oxide semiconductor device having improved block performance, and to a greatly improved integrated circuit performance.

In general, by using frequency (70MHz ~ 120MHz) frequency commonly used in frequency modulation (FM) broadcasting, music played from various multimedia terminals such as MP3 player, MP3 phone, portable CD player, personal computer or notebook PC It can be wirelessly transmitted to the FM tuner of a radio or home acoustics, and can be listened to through a speaker in a vehicle or a speaker of a home acoustics.

The block diagram of the FM transmitter chip according to the related art is shown in FIG.

The FM transmitter chip passes through the pre-emphasis circuits 110 and 210 and the pre-emphasis circuit that continuously increase the high frequency signal contained in the audio signals L and R input to the left and right channels. An audio block consisting of a limiter (120, 220) having a function of maintaining a level of one left and right audio signal, and a low pass filter (LPF, 130, 230) that removes frequencies higher than the left and right audio signal bands. block, 100, 200, a stereo multiplexing block (stereo MPX block, 300) that modulates the left and right audio signals passing through the audio block with a pilot signal of 38 kHz, and a reference frequency. Oscillator (410) to generate and crystal elements connected to the oscillator, including the clock frequency and phase frequency detector required for stereo multiplexing, Oscillator block 400 consisting of a plurality of frequency dividers (420, 430, 440) function to reduce the run frequency by an integer multiple, and the RF oscillator 610 passed through the frequency divider 510 A PLL frequency synthesizer block 500 comprising a phase frequency detector 520 and a loop filter 530 for adjusting the frequency and phase of the signal generated by the same as the reference signal; It comprises an FM frequency modulation block 600 including an RF oscillator 610 and an RF amplifier 620 for amplifying a frequency modulated signal to a predetermined level.

Stereo signal transmission uses the same method as the conventional FM airwave broadcasting method as follows. To create and transmit a stereo mixed signal, first generate a signal corresponding to the sum (L + R) and difference (LR) of two different audio signals inputted left and right, and then create a 19 kHz signal which is a stereo pilot tone. A 38 kHz carrier signal is then generated and amplitude modulated (LR).

Amplitude modulation of the (L-R) signal generates two (L-R) signals facing up and down 15 kHz around 38 kHz, that is, between 23 kHz and 53 kHz. The amplitude modulated (L-R) signal is mixed with both the (L + R) signal, the pilot tone, and 19 kHz to be transmitted after frequency modulation. The receiver detects that the input signal is stereo based on a 19 kHz pilot tone and uses the (L + R) and (L-R) signals to stereo demodulate the original L and R signals.

An important part of determining the quality of the stereo audio signal generated in the audio transmission chip is the stereo multiplexer (MPX) 300 block in FIG. 1 that affects the waveform of the chopper clock of 38 kHz used for multiplexing. Accordingly, the magnitude of the noise component in the mixed signal generated from the MPX is determined.

That is, in the frequency domain, the harmonic noise component does not exist in the most ideal sinusoidal file (see FIG. 2), and the harmonic component increases as the waveform deviates from the sinusoidal waveform, and the harmonic component passes through a system having nonlinear characteristics. It generates a noise signal by intermodulation action.

In the stereo multiplexing method adopted in the conventional audio transmission chip, sampling of the right input (R) signal and the left input signal (L) is performed once per chopper waveform, i.e., two stages using the chopper signal as shown in FIG. In this case, a chopper waveform is a square wave, and as shown in FIG. 4, it can be seen that there are countless harmonic signals in the frequency domain.

That is, a noise component increases due to intermodulation caused by harmonic components in the stereo-modulated mixed signal, and as a result, the quality of the audio signal is degraded. Degradation in the quality of the MPX audio signal directly affects the actual audio output quality through the loudspeakers of car and home audio equipment where the audio transmission chip is mainly used, and becomes unsatisfactory for its purpose as an audio transmission chip. In order to partially solve this problem, the bandpass filter is used outside the chip to remove harmonic components caused by square waves, thereby avoiding audio quality degradation.

However, in the conventional audio transmission chip, bipolar element technology is used in all circuit implementations except the frequency synthesizer. Bipolar semiconductor devices have high gain inherent characteristics, making it easy to implement an oscillator circuit required for a crystal oscillator and an FM oscillator. On the other hand, due to the large area occupied by the device, the final chip size of the audio transmission integrated circuit using the same also increases, which leads to an increase in manufacturing cost and makes it difficult to adopt a thin and thin package. In other words, the space occupied by the internal circuit board of the small portable terminal, which is the main use of the chip, is increased, which is a limiting factor for the miniaturization of the entire module.

In addition, the conventional stereo multiplexing method is the most basic implementation method of sampling each input signal of left (L) and right (R) once per period using a square wave of 38 kHz. In this case, the waveform of the square wave is an ideal sine wave. Due to the large deviation from the shape, the mixed signal generated in the MPX includes a large amount of harmonic noise components and intermodulated noise components due to harmonics. To improve this problem, a method of increasing the number of sampling of left and right signals can be taken. However, since the chopper frequency is increased to more than 38 kHz, there is a problem that cannot be practically adopted.

The present invention solves the problem of deterioration of the audio signal in the frequency modulated wireless audio transmission chip as described above, and performs 8-state weighted stereo multiplexing of the stereo modulation block of the wireless audio transmission chip for advanced sound transmission. It aims to improve the stereo audio signal quality by improving the low noise characteristic and to reduce the number of external devices such as band filter. Complementary metals, including stereo multiplexed blocks, implement all component blocks of an audio transmission integrated circuit with pure complementary metal oxide semiconductor (CMOS) device technology to reduce chip operating power consumption and reduce final chip size. An object of the present invention is to provide a frequency modulated audio transmission integrated circuit using an oxide semiconductor device and a control method thereof.

A frequency modulated audio transmission integrated circuit using a complementary metal oxide semiconductor device according to the present invention for achieving the above object includes an audio block for inputting an audio signal, the frequency required for stereo modulation and FM carrier generation Multi-stage stereo modulation in at least three stages of an oscillator block and a frequency synthesizer block for generating and determining a signal, an FM modulation block for frequency modulating a mixed signal, and an audio signal A multi-state stereo multiplexing (stereo MPX block) is characterized in that it is composed of.

The stereo multiplexing modulation block modulates the frequency by an eight-step weighted stereo modulation scheme in the multi-stage stereo modulation. The stereo multiplexing modulation block is configured in eight steps, and the oscillation frequency of the crystal oscillator is set to 21.25 MHz or 21.28 MHz.

It is preferable to form the entire frequency modulated audio transmission integrated circuit as a pure CMOS (complementary metal oxide semiconductor) device.

In addition, a method of controlling a frequency modulated audio transmission integrated circuit using a complementary metal oxide semiconductor device according to the present invention includes an audio block for inputting an audio signal, and generates frequencies required for stereo modulation and FM carrier generation. A frequency oscillator block and a frequency synthesizer block to be determined, an FM modulation block to frequency modulate a mixed signal, and a multi-state stereo multiplexing of an audio signal A method for controlling a frequency-modulated audio transmission integrated circuit comprising a stereo multiplexing modulation block (stereo MPX block), wherein the stereo multiplexing modulation block is configured to perform multi-step stereo modulation in at least three or more steps.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 5 is a block diagram illustrating a frequency modulated audio transmission integrated circuit using a complementary metal oxide semiconductor device using eight-step weighted stereo multiplexing according to the present invention. FIG. 6 is a clock signal diagram for driving an eight-step weighted stereo multiplexing switch according to the present invention. 7 is an eight-step weighted stereo multiplexing block diagram of the present invention, FIG. 8 is a conceptual diagram of a switch block for eight-step weighted stereo multiplexing of the present invention, FIG. 9 is a sine wave and a digital sine wave comparison diagram, and FIG. Weighted Stereo Multiplexing Comparison Diagram, FIG. 11 is a two- and eight-step weighted stereo multiplexed spectrum simulation comparison.

As shown, the present invention includes an audio block 100, 200 for inputting an audio signal, and an oscillator block for generating and determining a frequency required for stereo modulation and generation of an FM carrier. 400 and a frequency synthesizer block 500, an FM modulation block 600 for frequency modulating the mixed signal, and an audio signal in at least three stages. stereo stereoxing (stereo MPX block) 700.

The stereo multiplexing modulation block 700 modulates the frequency by an eight-step weighted stereo modulation scheme in the multi-stage stereo modulation, and in particular, the oscillation frequency of the crystal oscillator is 21.25 MHz or 21.28 MHz.

Further, it is more preferable to form the entire frequency modulated audio transmission integrated circuit as a pure CMOS (complementary metal oxide semiconductor) device.

The operation of the present invention configured as described above will be described in more detail, but the same components as in the prior art will be described by applying the same reference numerals.

As described above, in order to create and transmit a stereo mixed signal, first, a signal corresponding to a sum L + R and a difference LR of two input audio signals, left and right, is first generated. A 19 kHz signal, which is a stereo pilot tone, is generated and then a 38 kHz carrier signal in phase is amplitude modulated (LR).

Amplitude modulation of the (L-R) signal generates two (L-R) signals facing up and down 15 kHz around 38 kHz, that is, between 23 kHz and 53 kHz. The amplitude modulated (L-R) signal is mixed with both the (L + R) signal, the pilot tone, and 19 kHz to be transmitted after frequency modulation. The receiver detects that the input signal is stereo based on a 19 kHz pilot tone and uses the (L + R) and (L-R) signals to stereo demodulate the original L and R signals.

At this time, as an important part of determining the quality of the stereo audio signal generated in the audio transmission chip, in the present invention, the chopper clock (chopper clock) used for multiplexing as the stereo multiplexing modulation block 700 in FIG. The waveform determines the magnitude of the noise component in the mixed signal generated from the MPX.

The present invention uses a 8-state weighted sampling method for stereo multiplexing of an audio transmission chip to approximate a sine wave having a high frequency of 608 KHz as a fundamental wave (see FIG. 6). Digital sine waves can be obtained to minimize noise components due to multiplexing harmonics and to greatly improve the quality of the transmitted audio signal, thereby optimizing the quality of the final sound played through in-car or home acoustics. Can be.

8-state weighted stereo multiplexing is a method of creating a digital sine wave corresponding to the frequency half period of the sine wave divided into eight stages. FIG. 7 shows a corresponding block and FIG. 8 shows a series of switches and resistor circuits. It shows the corresponding circuit configured.

The eight-stage weighted stereo multiplexing is performed by seven switch operations corresponding to the upper and lower input signals. When the required resistance values from R0 to R6 are determined for 8-step stereo multiplexing, the values from the lowest to the maximum output through each resistor are calculated according to the appropriate switch operation. Based on this, the 8-state weighted sum is calculated. You can get it.

When the output value weights according to the switch circuit resistance values and the sine value weights when the half period of the actual sine wave is divided into eight equal parts are calculated and compared, respectively, the value of the output value and the output value weight by the individual switch operation are calculated at the corresponding angle of the actual sine wave. It is calculated quite similarly to these. It can be seen from FIG. 9 that the digital sine wave generated based on the eight-stage weight is closer to the actual sine wave.

FIG. 10 shows the results of computer simulation of eight-stage weighted stereo multiplexing. In comparison with the basic two-stage stereo multiplexing method used in the conventional audio transmission chip, the waveform of the digital sine wave produced in the eight stages of the present invention is shown. It shows the difference in the approximate sine wave. That is, it can be an optimal stereo multiplexing method that can enhance the quality of the reproduced signal after transmission while preserving the original input signal as much as possible. Computer simulation results for the comparative harmonic and noise components can be seen in FIG. 11.

An eight-stage stereo multiplexing requires an MPX clock of 608 kHz and uses crystals with oscillation frequencies of 21.28 MHz and 21.25 MHz, taking into account the comparison frequency settings of the frequency synthesizer.

This multistage weighted stereo multiplexing circuit, including other building blocks of the audio transmission chip in the present invention, is implemented using pure CMOS device processing techniques.

Although the preferred embodiments of the present invention have been illustrated and described above, the present invention is not limited to the above-described embodiments, and the present invention is not limited to the above-described embodiments without departing from the spirit of the present invention as claimed in the claims. Anyone skilled in the art can, of course, make various changes and make such changes as fall within the stated claims.

As described above, according to the present invention, by adopting a multi-stage stereo multiplexing circuit in the MPX of the frequency modulated audio transmission chip, it is possible to minimize the noise components that can be included in the transmission signal, thereby improving the quality of the reproduced audio signal compared to the conventional products. have. In addition, by adopting pure CMOS device technology for designing and manufacturing FM audio transmission chip including MPX block, chip operating power consumption can be lowered to 50% or less compared to the semiconductor device technology used in conventional products. In addition, the chip can be implemented in a small size of less than 1/2, thereby increasing the price competitiveness of the product.

In addition, it is possible to reduce the manufacturing cost of the audio transmission module by using the crystal of the oscillation frequency 21.25MHz, which is widely used in the home wireless telephone of 900MHz band. Therefore, the frequency-modulated audio transmission chip according to the present invention has the advantage of greatly saving battery power due to low power consumption and miniaturization of the chip, and can be effectively embedded and used in a portable multimedia terminal having a compact internal mounting structure. Has

Claims (8)

An audio block for inputting an audio signal, an oscillator block and a frequency synthesizer block for generating and determining frequencies required for stereo modulation and FM carrier generation, and a mixed signal FM modulation block for frequency modulation and a stereo multiplexing modulation block (stereo MPX block) for multi-state stereo multiplexing the audio signal in an eight-step weighted stereo modulation scheme. A frequency modulated audio transmission integrated circuit using complementary metal oxide semiconductor devices. delete The method of claim 1, And a stereo multiplexing modulation block in eight steps, wherein the oscillation frequency of the crystal oscillator is set to 21.25 MHz or 21.28 MHz. The method of claim 3, wherein And a frequency complementary metal oxide semiconductor (CMOS) device, wherein the entire frequency modulated audio transmission integrated circuit is formed of a pure CMOS (complementary metal oxide semiconductor) device. An audio block for inputting an audio signal, and an oscillator block, a frequency synthesizer block, and a mixed signal for generating and determining the frequencies required for stereo modulation and FM carrier generation. A control method of a frequency modulated audio transmission integrated circuit comprising an FM modulation block for frequency modulation and a stereo MPX block for multi-state stereo multiplexing an audio signal, The stereo multiplexing modulation block is a control method of a frequency modulation audio transmission integrated circuit using a complementary metal oxide semiconductor device, characterized in that the audio signal is configured to multi-stage stereo modulation in an eight-step weighted stereo modulation scheme. delete The method of claim 5, The stereo multiplexing modulation block is composed of eight levels of stereo modulation, but the oscillation frequency of the crystal oscillator is 21.25MHz or 21.28MHz, characterized in that the control method of the frequency modulation audio transmission integrated circuit using the complementary metal oxide semiconductor device. . The method of claim 7, wherein A method for manufacturing a frequency modulated audio transmission integrated circuit using a complementary metal oxide semiconductor device, characterized in that the entire frequency modulated audio transmission integrated circuit is formed of a pure CMOS (complementary metal oxide semiconductor) device.

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