With the rapid development of the automotive industry, in-vehicle wireless headset chargers will be widely used in high- and mid-end cars, and they will exhibit the characteristics of versatility, portability, and fashion. More and more car owners can enjoy the convenience of answering the phone while driving, and can listen to various high-fidelity music in their spare time.
Car wireless headsets refer to conventional car chargers powered by car batteries (12V for cars, 24V for trucks) combined with the latest wireless headset technology, which can be widely used in various portable, handheld devices, and car wireless answering fields.
Such as: application scenarios with car mobile phones, car PDAs, car GPS, etc.; the power supply part of car wireless headsets should consider not only the function of car charging, but also the actual needs of lithium battery charging (constant voltage CV, constant current CC , Overvoltage protection (OVP), and the harsh environment of the car battery (transient spike voltage, system switching noise interference, EMI, etc.).
Therefore, the power management IC selected for the car wireless headset solution must also meet: high voltage resistance, high efficiency, High reliability, low frequency (conducive to EMI design) switching power supply chip. For the wireless part, it is necessary to consider the harsh environment of the vehicle, such as interference and vibration, as well as the actual needs of playing music and call sound quality.
Therefore, it is a very good design plan to select Bluetooth wireless headsets for design, which can meet various application requirements and quickly occupy the market. The Bluetooth IC we selected must have stable performance, reliable transmission, and excellent sound quality. Therefore, the Realtek RTL8763B series Bluetooth headset solution is The best choice.
This product has multiple features such as versatility, portability, fashion, and safety. It is one of the essential equipment that car owners love. It is expected that more and more brands will join this blowout market. This product has the following characteristics:
Versatility: This car wireless headset charger is equipped with four AC adapters for American, British, Austrian and European regulations; it combines car charger, direct charge, USB, and Bluetooth headset charging into one to meet different conditions Charging; USB output interface can charge electronic products.
Portability: Portability is a major trend in the development of today's electronic products. The unique folding car charger design is used to reduce the product volume to 6.9×5.6×3.1cm, which is extremely convenient to carry.
Fashion: For the high-end consumer group of car owners, the fashion of car chargers is also valued by manufacturers. Generally use ABS material and piano paint process, which is not only fashionable and exquisite, but also feels very good.
Safety: The product has passed CCC, UL, FCC, CE and other international safety performance tests, and is guaranteed by insurance companies, which strongly guarantees the safety of use performance and consumer rights.
The charging function of the car wireless headset player is to facilitate car owners to use the car power to charge digital products anytime and anywhere. The function of the wireless headset is to help people easily get rid of the danger of making and answering calls while driving.
Such products generally have overload protection, short-circuit protection, high-voltage input protection, high-temperature protection, and four-fold safety protection functions to ensure safe use.
The car charger function of the car wireless headset player can be used in the car as well as in the home, realizing the three-in-one multi-function use of car charger, direct charging and USB charging. The function of the wireless headset is to facilitate the application of driving and answering calls and music entertainment, and it can also play the role of music in car entertainment.
The so-called FM transmission is to act as an FM radio station, the frequency is between 76-108M, we choose QN8027. What is the significance of this FM transmission?
For example, some consoles or rear-seat entertainment systems play music, but there is no speaker or the speaker is a bit worse. When you use FM to transmit, you can find the FM radio frequency point in the original FM, and listen to the radio to receive the music.
Then use the original audio system to put it out, and everyone in the car can enjoy the high-quality enjoyment brought by this music. So how is this system implemented? The circuit components, the circuit is mainly composed of three parts, the car charging circuit, BT audio, and Digital FM, which are described separately below.
QN8027 is a high-performance, low-power, full-featured single-chip stereo FM transmitter, suitable for portable audio/video players, car accessories, mobile phones and GPS personal navigation devices. QN8027 covers frequencies from 76 MHz to 108 MHz in 50/100/200 kHz steps for global FM band support.
QN8027 also supports RDS/RBDS data transmission. QN8027 integrates a complete transmitter function, from stereo audio input to the RF antenna port for personal area broadcasting in the global FM band. It includes variable input gain programming, selectable pre-emphasis, precise low-spurious MPX stereo encoding and pilot tone generation, low-noise PLL-based modulation, and on-chip power amplifier with variable output level and RF bandpass filtering, To ensure the best emission spectrum PU etiquette.
The integrated crystal oscillator and the on-chip digital calibration circuit eliminate external tuning components, making tuning free to manufacture. Supporting 12/24MHz reference clock allows the chip to use the ready-made system clock. The integrated saturation detection and programmable audio interface eliminate distortion, optimize audio fidelity, and support a wide range of input audio levels. Low-power idle mode extends battery life.
The integrated LDO can be directly connected to the battery and provides high PSRR for noise suppression, especially the TDMA noise of GSM/GPRS phones. QN8027's small footprint, high integration with a minimum number of external components, and support for 12/24MHz clock frequencies make it easy to integrate into a variety of low-power portable applications with small form factors.
The integrated low phase noise digital synthesizer and extensive on-chip automatic calibration ensure robust and consistent performance over temperature and process variations. The integrated voltage regulator can be directly connected to the battery and provides high PSRR for excellent noise suppression. Low-power idle mode extends battery life. ESD protection is on all pins. QN8027 is made with high reliability CMOS process. See below:
The audio and voice signals processed by Bluetooth decoding reach the signal input network composed of C19, C18, R2 and R3 through the PIN3 and 4 pins of RTL8763B. C18 and C19 are the signal coupling capacitor input left and right channels.
Crystal X2 is a 12mhz crystal oscillator. Capacitors C13 and C14 are used to provide proper crystal oscillator load matching capacitance. Resistor R4 and R20 are the I2C communication interface resistance of QN8027 and MCU R7F0C807. C2, C1, L3, and Q1 form the tuning application of the IC RF oscillator.
The modulated radio frequency output is composed of filter networks L3 and C1 at the antenna. The working network of this filter is to eliminate harmonics, and the whole circuit is very simple.
The RT8763B series is a general term for products such as Realtek Wireless Bluetooth (RTL8763BM) and stereo audio solutions (RTL8763BF / BFR RTL8763BS, RTL8763BA). RT8763B consists of an ARM core and an ultra-low-energy DSP core with high-efficiency computing power, high-performance audio codec, power management unit, ADC, ultra-low radio frequency transceiver and intelligent I/O distribution controller.
In addition, Realtek has developed a complete set of parameter configuration tools, EVB toolkits, production line production test suites, including controller hardware and software, to provide customers with a simple and flexible program rapid design program, enabling customers to quickly and effectively Mass production and rapid occupation of the market.
The system power supply is mainly outputted by MC34063 to output 5v. MC34063 is a very classic DC-DC circuit, which is still widely used in car charging circuits for many years. The main reason is that the circuit is simple and cheap.
There are a large number of application design circuits on the Internet, so I don't need to introduce too much here. Since QN8027 requires I2C communication, this system introduces a Renesas MCU R7F0C807 with few pins and very simple application to complete the initialization of QN8027 and system control actions. The specific application is uploaded in the attachment.
The software development of this system is part of the RTL8763B software development work. The basic functions of the wireless headset can be completed through the GUI visualization tool configuration tool. I will not introduce it here. The other is the program development of Renesas MCU and QN8027. QN8027 is controlled by IIC. QN8027 has certain requirements for initialization, and the reference clock is also particular about it, which is very related to hardware circuit design.
The following focuses on the correct development of the QN8027 program, the initialization program is as follows:
1. Write data to QN8027 register 0x00=0x81; //Reset all registers of QN8027 to default values
2. 20ms delay
3. Write data to QN8027 register 0x03=0x50; //Set QN8027 as external sine wave clock input (related to hardware design)
4. Write data to QN8027 register 0x04=0x33; //Set 12MHz clock frequency (related to hardware design)
5. Write data to QN8027 register 0x00=0x41; //QN8027 finite state machine verification
6. Write data to QN8027 register 0x00=0x01; // QN
7. 20ms delay //Add 20ms delay to wait for the completion of QN8027 finite state machine verification
8. Write data to QN8027 register 0x18=0xE4; //Improve SNR
9. Write data to QN8027 register 0x1B=0xF0; //Maximize QN8027 transmit power
10. Write data to QN8027 register 0x01=0x7E; //Set transmit frequency
11. Write data to QN8027 register 0x02=0xB9; // Give up QN8027 PA shutdown function when there is no audio signal input
12. Write data to QN8027 register 0x00=0x22; //Transmit
The specific initialization reference code is as follows:
It must be particularly emphasized that when switching the FM transmitting radio frequency point, it will be found that at the high frequency point, that is, when the 8th-9th bit of the FM frequency stored in the 0x0 register has a value, the transmitting antenna voltage amplitude will decrease.
Later, when I found this high frequency point, I need to change the values of the two registers. When I adjust the frequency, I first let fm enter the standby mode, and when the new frequency point is set, let fm be in the transmit mode, so Effectively solve the problem of abnormal output amplitude. The reference code is as follows:
► Scenario application diagram
► Product entity diagram
► Showcase photos
► Scheme block diagram
► Core technical advantages
BT5 dual mode
– Cortex-M4 80MHz + DSP 160MHz + codec
– 24Bit x 96KHz analog output/input
– 24Bit x 192KHz I2S interface/ SPDIF
– USB audio/charger/ 2 x microphone/ AEC/ NR
--Bluetooth classic/BLE concurrency
– Ultra-low power consumption 7mA (A2DP)
-Open SDK platform using internal DSP
– QFN40 / 48/68 / TFBGA 4.5x6
– Support SBC, AAC, mSBC, MP3, FLAC.
-Built-in sound effects to enrich the audio listening experience
−10 band EQ, DRC, widening, virtual bass, etc...
– DSP effects also apply to the line input path
► Solution specifications
Dimensions 100mm (length) x45mm (width) x53mm (height)
Power supply DC 12V-24V
Music format MP3 / WMA, etc.
Working current <30mA
Bit rate 32K bps- 256K bps
FM frequency range 88.1 to 107.9MHz, step 0.2MHz
Channel switch press CH key
BT stereo 24-bit DAC 102dBA SNR, stereo 24-bit ADC 97dBA SNR
Harmonic distortion ≤0.05%
Working temperature -5°C~40°C
FM transmission distance <5m
Attached user manual, attached cable, USB cable,
Additional 0.5A fuse
IC MCU 16BIT 152KB FLASH 28SSOP
IC MCU 8BIT 64KB FLASH 100TQFP
IC MCU 8BIT 768B OTP 28SOIC
IC MCU 8BIT 3.5KB OTP 28SSOP