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Compact design of on-board AM/FM radio

Click： Time：2017-05-31 17:02:43

With the automobile from the means of transport change into leisure, entertainment as one of the personalized consumer goods，Consumer demand for automotive entertainment continues to improve，The auto industry is also facing strong market pressure，Costs are urgently needed to reduce costs without sacrificing effectiveness，This is particularly true in the entry-level car market，Consumer demand for low-cost vehicles has allowed the annual growth rate of the low-end media entertainment market to exceed 10%。AM/FM radios are characterized by their low cost, high sound quality and so on，It is especially popular。How to design a cost control requirement，The ability to achieve high quality audio enjoyment of broadcast audio products to meet the needs of this field for cost reduction and simple design becomes the focus of the industry。We can imagine the constant improvement and constant innovation of the radio，The development of the radio is becoming more and more important。

Usually traditionalradioThe solution is to use FM / am radios made up of split integrated units，Its main composition is：antenna、The input circuit、High frequency amplifier circuit、Mixing circuit、Local oscillator circuit、Intermediate frequency amplification circuit、Discriminator circuit、Low frequency power amplifier circuit、Speaker, etc。The design of the scheme is very complicated，And the sound quality is loudC，The audio signal is badly distorted，Evaluation in all respects is not the best solution。This article will design a new one、Low-cost、To useRFCMOSSingle chipAM/FMRadio solutions，Compact microcontroller，Combined with ultra low cost audio sound processing, DSP and hi fi audio power amplifier，Few components are realized、Few go line、Minimum volume、Very low cost high quality AM/FM car radio solution.

1 Device selection

In order to realize low - cost car or ultra - application low cost targets，The primary task is to select the appropriate microcontroller (MCU) and the AM/FM low if tuner。FreescaleSemiconductor company's latestMC9S08QGLow-end micro controller series，Its processing kernel、The peripheral equipment、Power saving and development tools，cost、energy、Ideal solution for efficiency sensitive control applications。The core device for this wireless controller design is the Freescale, the only 16 pin MC9S08QG8 in the series。MC9S08QG8High performance is adopted、The low power HCS08 kernel has a high integration device in the 8 bit microcontroller series，Built-in8K FLASHstorage、512 bytes RAM、SCI/SPI/IICinterfaces、8 bit modulus timer module、A/DModule etc。MC9S08QG8 MCUIntegrated with those usually only larger、The performance of the more expensive components can have, including the background debug system and can be simulated with online real-time bus capture (ICE) function, debugging and simulation interface with a single line (BDM), also includes a programmable 16 bit timer / pulse width modulation (PWM) module (TPM), is one of the modules similar products in the most flexible and most economical.

Another major chip is a low if tuner，Select NXP semiconductor company TEF6621。TEF6621，An extremely successful RFCMOS single-chip on-board radio solution series for NXP (NXP)。An updated version of TEF6601 and TEF6606, which are widely used in the industry，TEF6621The tuner allows us to make sure that more exciting features are installed in smaller spaces in the car radio system。The innovative features of tuners are all key rf components一一Include：Voltage-controlled oscillator，Ceramic filter，Intermediate frequency transformer coil，Low noise amplifier and automatic gain control，Only 32 low-cost, passive peripherals are required(Capacitance、resistance、Inductance and transistor)。In addition，By means of special large signal processing，This low-frequency tuner can support high performance requirements for car radio applications。Vehicle design based on TEF6621radioThe system will be handled with more perfect weak signal processing、FMNoise blanking、The multi-path inhibition capability of noise is more powerful、It is ideal to press noise suppression and other functionsradioSolution。

The rest is the digital audio signal processing subsystem and the audio sound processing amplifying output circuit，This scheme adopts PT2313 to deal with system audio，PT2313LAudio processor has high、Bass control function and high loudness (heavy bass) control function，It also has a three-way stereo input port，And the gain can be controlled by microcontroller，It also has four independent power amplifier ports，And the output can be controlled by the microcontroller、The functions of balance, mute and shutdown can also be controlled by microcontroller，The minimum step quantity is1.25 dB。

Adopt ST semiconductor 4 * 41W four bridge audio amplifierTDA7388，TDA7388Is a new technology AB audio power amplifier，Useflexiwatt 25Package design，Because of its high output power capability，Low distortion and low output noise，Mute function，Low external element number，Internal fixed gain(for26 dB)，No external compensation，No starting capacitor and other characteristics，Become high-end carsradioFirst choice。

MC9S08QG8The internal IIC module realizes data communication control through IIC bus and tuner TEF6621 and sound processing and volume adjuster PT2313，To achieve the choice of radio frequency and audio volume adjustment。And throughMC9S08QG8The microprocessor controls the entire audio high power part，Achieve standby(standby)、To turn it off(shut up)Such as control。

As for other peripheral devices, general purpose can be used，For example, AM/FM antennas、Liquid crystal display USES 16x2 character LCD，As well as a coded potentiometer for tuning，This part of the circuit application is mature technology。

2 Audio sound processing and equalization technology

With the development of science and technology，Radio programs from editing、Make to propagate、Send out，More advanced technical equipment is used，The quality of the program has also been greatly improved。though，The matching problem between the receiving antenna and the network and the noise and attenuation of the audio signal in the transmission process are still puzzling the realization of the high fidelity audio enjoyment Technology，The main reason is that engineers are very little concerned with the working state and settings of audio processors。

The broadcast audio signal has a large nonlinearity in the processing，For audio processing devices，Not only does it include compression of the signal、confine、clipping、Extended equal processing，And the location of the audio processing equipment installation、The wire length，In addition, there are strict requirements on anti-interference ability in high electromagnetic fields

Audio communication media features，That is, the physical properties of sound waves，Audio recording and production in various ways，Mainly including mold/number、number/Mode conversion、Data compression and sound synthesis。The editing methods of audio data are also diverse，Generally speaking, the processing methods of audio signals can be broadly divided into two categories：One is digital audio mode，The other is the analysis of a synthetic approach.

Regular audio is a continuous analog signal，A continuous curve is used to represent it，Sonic wave。The curve of the analog signal no matter how complex，At any given moment, can be decomposed into a series of linear superposition of sinusoids