This article refers to the address: http:// In recent years, with the multi-functionality of mobile phone applications and the popularity of MP3/MP4 media players, FM reception has become an essential function. Some insiders have been optimistic that by 2008, FM mobile phones can account for more than 40% of the total, such a large terminal market is bound to lead to an increasing demand for FM receivers (FM Tuner). At the same time, with the rapid development of integrated circuit design and manufacturing technology, FM Tuner began to evolve from the modular era to the SoC era. The single-chip FM Tuner technology is improving day by day, and its performance has been greatly improved compared to the previous one. It has high receiving sensitivity, can support mono and stereo switching, and starts to support wireless data services (RDS). ) / Radio Broadcast Data Service (RBDS). The RDA5800 chip is a fully integrated CMOS FM Tuner chip independently developed by RDA Micro. It has the advantages of high integration, high performance, low cost and low power consumption. It is currently highly competitive in the market. A product of superiority has received widespread attention from industry experts and application engineers. Let's discuss the features and design techniques of this chip. Basic features of the RDA5800 chip It uses SMIC's 0.18 micron RF CMOS advanced technology, the RF part uses a low IF structure, FM stereo decoding is implemented by a digital DSP, and the driver part integrates the voice amplifier into the chip, which effectively improves the chip. Performance, reduced cost of solution, and very good integration. The chip is packaged in a 4×4mm 24-pin QFN package. It integrates an LDO and crystal oscillator circuit. The total operating current is 16mA. It has automatic search, soft and silent, heavy bass, noise suppression, direct drive earplugs and other excellent performance. The main performance indicators of the RDA5800 chip are shown in Table 1. How the RDA5800 chip works The RDA5800 is mainly divided into two parts, analog and digital. The analog part includes a low noise amplifier (LNA), a limiter (Limiter), a quadrature image rejection mixer (MIXER), an adjustable gain amplifier (PGA), and a high precision mode that support all FM bands (76 to 108 M Hz). Digital converter (ADC), high precision digital-to-analog converter (DAC), synthesizer, and LDO for Power Supply. The digital part includes a speech processing DSP and a digital interface. The basic working principle is as follows: When the antenna receives the FM signal in the air, the signal is first amplified by the LNA and converted into a differential output voltage, which can effectively suppress noise inside the chip and on the PCB, and improve receiving sensitivity. In the RDA5800 chip, the LNA supports single-ended input operation, and only needs to ground another input terminal, which greatly simplifies the complex and sensitive input matching network of common RF circuits. Since there is no SAW bandpass filter at the FM input, there will be a lot of noise outside the FM band entering the chip. The limiter detects the magnitude of the LNA output signal voltage. When the threshold is reached, it will automatically be constant to prevent the LNA from being saturated due to out-of-band noise. The nonlinear distortion is generated; the mixer downconverts the LNA output signal to a low intermediate frequency while suppressing the image frequency. The low IF can avoid the problem that the zero-IF structure DC noise is difficult to eliminate, and reduce the input signal bandwidth of the ADC. The PGA amplifies the I and Q two-way IF signals of the MIXER output to the ADC, and its gain is dynamically generated by the DSP. Control, effectively reducing the dynamic range of the ADC input; the ADC uses a delta-sigma band through the sampling structure, which has high precision and low power consumption, and suppresses out-of-band noise, which is very suitable for processing, Low frequency signal. The ADC output includes both the low-frequency effective signal and the high-frequency noise. The signal and noise are simultaneously sent to the DSP for processing. After the DSP completes the demodulation, the voice signal is sent to the left and right channel high-precision DAC. The DAC is also a low-pass filter that attenuates noise outside the speech band and then amplifies the speech signal through the volume control register and finally sends it through the integrated amplifier inside the chip. The core FM demodulation and speech processing work is done by the speech processing DSP. The DSP first downsamples and filters the data sent by the ADC through the digital filter, filters out the modulated high frequency noise, recovers the low frequency signal, and then recovers the low frequency signal. Demodulate the signal (MPX Decoder) to switch between mono and stereo, then load the adjustable subwoofer function and mute function. The frequency synthesizer generates a corresponding quadrature local oscillator signal to the MIXER according to the frequency setting, and its reference clock is 32.768 KHz because the higher harmonic energy of the 32K crystal in the FM band is small. The main module voltage-controlled oscillator (VCO) in the frequency synthesizer uses an on-chip inductor LC VCO structure and integrates the loop filter into the chip. The RDA5800 integrates a crystal oscillator circuit to directly support the off-chip crystal. The number of components on the chip and the layout area of ​​the chip are greatly reduced, the reliability is improved, and the local oscillator signal has good phase noise and adjustment flexibility. The chip integrates the LDO to power the entire chip. It has a high power supply voltage rejection ratio, which ensures that the chip can work normally in the voltage range of 2.7 to 5.5V. The chip supports normal battery direct power supply, which simplifies the use of the chip. The RDA5800's interface supports two and three wires with a GPIO digital interface. Programming is simple, only need to write frequency points or directly search, the chip will automatically complete other conversion work. Application of RDA5800 Based on the schematic diagram of the RDA5800 application system, Figure 2 shows the application scheme of the RDA5800: J1 is a common earplug, the antenna is the grounding wire of the earplug, and L3 and C3 constitute the LC cavity, and the FM signal is not attenuated when DC grounding is provided. R1 is the pull-up resistor of the digital interface; C6 is the power supply filter capacitor, the actual PCB layout should be as close as possible to the chip, C4 and C5 are the DC coupling capacitors, and the characteristic resistance of the earplug constitutes an RC high-pass filter. Filter out the effects of low frequency noise. Since the subwoofer is adjustable, it can be pre-emphasized, C4 and C5 capacitors can be replaced by smaller value capacitors, and the attenuated signal can be used to save PCB area. Figure 3 is the evaluation board of the RDA5800. Compared with the traditional FM chip, it requires more than 20 components and 11×11mm PCB area. The advantage of the RDA5800 is obvious: the PCB area is only 6×6mm, and the number of peripheral components Less than 10. The RDA5800 is easy to use and cost-effective. It is the iconic product of the FM SoC era. It is suitable for all kinds of portable products with radio functions, including: mobile phones, notebook computers, MP3/MP4 media players, PDAs, independent FM radio, wireless headphones, etc. Single Phase Voltage Regulator Single Phase Ac Voltage Stabilizer,Single Phase Servo Motor Voltage Stabilizer,Single Phase Automatic Stabilizer Heyuan Electronic Technology Co., Ltd. , http://www.yqvoltagestabilizer.com
Table 1: Main performance indicators of the RDA5800 chip
Figure 1: Schematic of the RDA5800 system
Figure 2: RDA5800 application
Figure 3: Evaluation Board for the RDA5800