CN115278473B

CN115278473B - Bluetooth stereo system

Info

Publication number: CN115278473B
Application number: CN202210890773.6A
Authority: CN
Inventors: 冀云
Original assignee: Chongqing College of Electronic Engineering
Current assignee: Chongqing College of Electronic Engineering
Priority date: 2022-07-27
Filing date: 2022-07-27
Publication date: 2024-09-24
Anticipated expiration: 2042-07-27
Also published as: CN115278473A

Abstract

The invention discloses a Bluetooth stereo system, which mainly comprises a Bluetooth unit and an audio processing unit; data transmission can be realized between bluetooth unit and the audio processing unit, and bluetooth unit mainly includes: the Bluetooth module can run Bluetooth protocol stack software to realize data communication; the external processor is used for running external software. The invention can reduce the dependence on the mature Bluetooth module, improve the flexibility of external software design and bring possibility for selecting the implementation mode of the external software design with optimal cost performance.

Description

Bluetooth stereo system

Technical Field

The invention relates to a Bluetooth stereo system, belonging to the technical field of communication circuits and systems.

Background

Bluetooth is a low-power consumption and short-distance wireless communication technology, which is used as a new technology, can conveniently establish wireless connection to replace the traditional wired cable, has strong connection portability, and is designed to replace the wired cable of the interfaces on the existing personal computers, printers, fax machines, mobile phones and other devices. The address of each Bluetooth device globally supports networking working modes such as piconets, decentralized networks and the like, the application range is wide, in addition, the Bluetooth device has low power consumption and low cost, and compared with other communication devices, the Bluetooth device has easier design and development. For example, bluetooth headsets are a typical application of bluetooth technology.

Conventional headphones require a connection wire to the mobile phone and thus are very limited in use and cannot be used conveniently during movement. In contrast, bluetooth wireless headphones can solve these problems well, and are more competitive. The user's mobile phone can easily make and receive calls, whether in a pocket or briefcase, even in another room.

In the prior art, a stereo system based on the Bluetooth technology generally adopts a microprocessor, a Bluetooth module, an audio encoding and decoding module and a power control module which are mutually independent to realize system hardware, which obviously has the defect of low system integration level and complex circuit hardware design. The bluetooth stereo earphone design in the prior art also has a design scheme adopting a mature single chip, namely a single chip comprises a 32-bit microprocessor, and the microprocessor is used for running a bluetooth protocol stack, so that a user can easily add a bluetooth wireless technology into a system of the bluetooth stereo earphone, and the design scheme has the advantage of low development difficulty, but obviously has the defect of excessively relying on a single chip provider. In addition, the design of the audio processing unit is complex, a special audio decoding chip is needed, and the audio driving circuit is also limited by a power supply source in power driving capability, and an independent larger power supply source is needed.

Disclosure of Invention

Aiming at the problems and the shortcomings, the invention aims to solve the technical problems that: the Bluetooth stereo system can reduce dependence on a mature Bluetooth module, improves flexibility of external software design, and brings possibility for selecting an external software design implementation mode with optimal cost performance.

In order to solve the problems, the invention adopts the following technical proposal

A Bluetooth stereo system comprises a Bluetooth unit and an audio processing unit; the Bluetooth unit can realize data transmission with the audio processing unit, and is characterized in that:

The Bluetooth unit includes: the Bluetooth module can run Bluetooth protocol stack software to realize data communication; the external processor is used for running external software;

The audio processing unit comprises an audio decoding unit and an audio driving unit;

the Bluetooth module is a ZV4301 chip, the external processor is an FPGA processor, and the audio decoding unit is arranged inside the FPGA processor;

Further, the audio driving unit includes: the operational amplifier A1, a first driving module and a second driving module; the audio analog signal is connected with the negative input end of the operational amplifier A1 through a resistor RA; the negative input end of the operational amplifier A1 is also connected with the output end of the operational amplifier A1 through a feedback resistor RF, and the positive input end of the operational amplifier is grounded through a resistor RB; the output end of the operational amplifier A1 is connected with the input of the first driving module, and the output of the first audio driving module is connected with one terminal of the loudspeaker; the audio analog signal is directly sent to a second driving module, and the output of the second audio driving module is connected with the other terminal of the loudspeaker; the integrated subtractor chip for realizing signal subtraction is selected to replace the operational amplifier A1, the integrated subtractor chip is AD8276, 4 resistors with good matching values are integrated in the AD8276, the 5 th pin and the 6 th pin of the AD8276 chip are connected to form a feedback loop, the 1 st pin of the AD8276 chip is suspended, the 3 rd pin of the AD8276 chip is grounded, a circuit structure formed by the resistors RA, RB, RF and the operational amplifier A1 is realized, and the resistance values of the resistor RA and the resistor RF are equal.

Further, the first driving module and the second driving module adopt the same structure, and the structure is as follows: comprises a voltage amplifying part and a current amplifying part; the voltage amplifying part comprises an operational amplifier AP; the current amplifying section includes transistors Q1 to Q6; the base electrode of the transistor Q1 is connected with the output end of the operational amplifier AP, the collector electrode of the transistor Q1 is connected with the collector electrode of the transistor Q3, the collector electrode of the transistor Q1 is also connected with the collector electrode of the transistor Q5, and the emitter electrode of the transistor Q1 is connected with the base electrode of the transistor Q3; the emitter of the transistor Q1 is also connected with the base of the transistor Q5; the emitter of the transistor Q3 and the emitter of the transistor Q5 are both connected to one terminal of the speaker; the base electrode of the transistor Q2 is connected with the output end of the operational amplifier AP, the collector electrode of the transistor Q2 is connected with the collector electrode of the transistor Q4, the collector electrode of the transistor Q2 is also connected with the collector electrode of the transistor Q6, and the emitter electrode of the transistor Q2 is connected with the base electrode of the transistor Q4; the emitter of the transistor Q2 is also connected with the base of the transistor Q6; the emitter of the transistor Q4 and the emitter connection of the transistor Q6 are both connected to one terminal of the speaker.

The invention selects the mature ZV4301 chip to realize the Bluetooth module and makes improvement, in particular, the 32-bit microprocessor built in the ZV4301 chip is used for realizing the operation of the Bluetooth protocol stack, but the invention realizes the operation of external software on an external additionally-arranged processor. External software is used to implement various specific functional requirements that the bluetooth system needs to implement when placed in a specific application environment (e.g., a car bluetooth stereo application), similar to various APP applications. This appears to reduce the overall system integration (adding a single processor), but also brings about several advantages: not only can the dependence on mature devices such as ZV4301 chips be reduced, but also the flexibility of external software design can be improved (the development of various external software can freely select a processor, which inevitably brings flexibility to the development of external software), and the possibility of selecting an external software design implementation mode with optimal cost performance is brought.

In addition, the invention realizes larger power output based on low power supply voltage, the conventional Bluetooth chip, the microprocessor chip and the FPGA chip are all powered by a lower voltage power supply, such as common 3.3V, if the same power supply voltage is required to be used for supplying the audio driving circuit, the audio driving circuit is difficult to realize larger power output, and the audio driving circuit is obviously difficult to adapt to certain application requirements, and the audio driving circuit adopts the following design to solve the problem.

Drawings

FIG. 1 is a schematic diagram of the overall structure of the present invention;

FIG. 2 is a schematic diagram of an audio driver circuit unit

FIG. 3 is a schematic diagram of the driving module in FIG. 2;

Detailed Description

The invention relates to a Bluetooth stereo system, which mainly comprises a Bluetooth unit 1 and an audio processing unit 2;

The bluetooth unit 1 mainly includes: a microprocessor 11, the microprocessor 11 being capable of running bluetooth protocol stack software to enable data communication; a 2.4GHZ radio frequency module 12 and a baseband digital processing module 13.

With the continuous development of ultra-large-scale digital integrated circuit technology, the overall architecture of the core bluetooth unit of the bluetooth stereo system, as mentioned in the background, mainly presents the following conditions:

And (I) the method is realized by adopting mutually independent microprocessors and baseband digital processing units. For example, the partial circuits are realized as follows: 1. the main processor of the main board of the system is SIRFPRIMA chips, the Bluetooth stereo system adopts ARM architecture, and the system has the characteristics of low power consumption and high performance, provides a basis for smoothly running an operating system and application programs, and is also integrated with a GPS module. 2. The bluetooth baseband transmission device is implemented using a chip such as 8311a08 of CSR corporation. 3. A separate audio codec circuit chip is used.

And (II) a mature Bluetooth module such as a Bc03_Multimedia chip, a Bluecore-MM chip, a ZV4301 chip and the like is adopted. The Bluetooth stereo system is a mature chip with higher integration level, and a microprocessor, a radio frequency circuit and a baseband digital processing unit are integrated inside the chip, so that the Bluetooth stereo system can be realized only by external FLASH storage, an audio encoding and decoding circuit, an antenna and other necessary peripheral devices.

For example, the Bc03_Multimedia provided by the CSR company integrates the radio frequency and baseband protocols of Bluetooth, is externally connected with a Flash memory of 8M B, and can completely realize the 1.2 version of Bluetooth protocol by using the firmware provided by the CSR company to realize the communication of data and voice. It integrates therein even an open Kalimba DSP coprocessor and a 16-bit audio codec to support enhanced audio applications, it can support I2S and SPDIF digital audio interfaces, mainly applied to stereo headphones, car hands-free, high performance telephone headphones, enhanced audio applications, etc.

2. Bluecore5-MM chip integrates the radio frequency and baseband control of the Bluetooth system, 16 bit MCU of RISC structure and Kalimba DSP with performance as high as 64 MI/s in a single chip. Wherein the MCU (equivalent to an internal microprocessor unit) realizes a Bluetooth protocol stack and application software, and the DSP realizes audio and voice processing and encoding and decoding of the streaming media music file.

3. The ZV4301 chip contains a 32-bit microprocessor that is used to run the bluetooth protocol stack, but in use requires an external audio codec unit, typically a dedicated audio codec chip. An external audio coding and decoding unit commonly uses a chip such as WM8731, which is built with analog-to-digital conversion and digital-to-analog conversion, the bit number of digital audio is 16-32 bits, and the sampling rate is up to 96KHZ.

In summary, most of these designs use an internal integrated microprocessor unit to implement the operation of the bluetooth protocol stack and the external application software at the same time, and compared with the system, the system has an integrated level (i.e., the system is implemented by using a microprocessor and a baseband digital processing unit that are independent of each other). The design is realized by matching with an audio coding and decoding chip.

Based on the above analysis, compared with various schemes in the prior art, the invention selects the mature ZV4301 chip to realize the Bluetooth module and makes improvement, specifically, the 32-bit microprocessor built in the ZV4301 chip is used for realizing the operation of the Bluetooth protocol stack, but the invention realizes the operation of external software on an external additionally arranged processor. External software is used to implement various specific functional requirements that the bluetooth system needs to implement when placed in a specific application environment (e.g., a car bluetooth stereo application), similar to various APP applications. This appears to reduce the overall system integration (adding a single processor), but also brings about several advantages: the dependency on mature devices such as ZV4301 chips can be reduced, the flexibility of external software design can be improved (various external software development can freely select processors, which inevitably brings flexibility to external software development), the possibility of selecting an external software design implementation mode with optimal cost performance is brought, for example, an external processor additionally arranged in the invention can be realized by an FPGA device, the FPGA device is a semi-custom ultra-large-scale integrated circuit, various processing and control applications can be realized in a pure hardware mode, and the FPGA device of various grades can be used, even if a conventional processor kernel is usually built in a medium-low end product, a practical storage unit matched with the processor kernel can be called inside, so that the system can be obtained.

And, because the FPGA contains a large amount of digital logic resources besides the processor core.

In order to further utilize FPGA hardware resources and improve the integration level, the invention places the audio coding and decoding function usually realized by a peripheral single chip in the FPGA, realizes the audio coding and decoding function through hardware description language development to provide design flexibility and a special-purpose stronger audio coding and decoding unit circuit, and is beneficial to later design modification. Of course, in the implementation scheme of audio encoding and decoding, the implementation of the special decoding chip is the fastest scheme, but because the special decoding chip or the FPGA has parallel processing structures, the special decoding chip or the FPGA can be suitable for being used as a high-performance data path processor, such as digital filtering, fast Fourier transform, discrete residual spin transform and the like, and becomes a key component in a high-performance digital signal processing system. The algorithm of the codec can be realized completely by digital logic resources inside the FPGA. Meanwhile, the processor core can be integrated in the FPGA, and the FPGA can be used for realizing the external software running function.

2. Implementation and working principle of audio processing unit

The audio processing unit mainly comprises an audio decoding unit and an audio driving unit.

In general, the audio decoding unit is composed of a codec chip, and in conventional applications, a microphone input signal enters the codec chip after being amplified by audio.

As described above, the running of the external software is implemented on the external additional processor, and the additional external processor is implemented by the FPGA device, specifically, the siren FPGA with the built-in ARM architecture kernel is selected for implementation; in order to further utilize the FPGA hardware resources and improve the integration level, the invention places the audio coding and decoding function usually realized by a peripheral single chip in the FPGA to realize the audio coding and decoding function through hardware description language development so as to provide design flexibility and special-purpose stronger audio coding and decoding unit circuits, and is beneficial to later design modification,

The audio codec unit finally drives the speaker through the audio driving circuit. In the design of the audio driving circuit, the invention realizes larger power output based on low power supply voltage, the conventional Bluetooth chip, the microprocessor chip and the FPGA chip are all powered by a lower voltage power supply, such as common 3.3V, if the same power supply voltage is required to be used for supplying the audio driving circuit, the audio driving circuit is difficult to realize larger power output, and the audio driving circuit is obviously difficult to adapt to certain application requirements, and the audio driving circuit adopts the following design to solve the problem that the audio driving circuit unit comprises: the operational amplifier A1, a first driving module and a second driving module; the audio analog signal is processed at the same time, on the one hand, the audio analog signal (the signal which is directly used for driving the loudspeaker after being processed) is connected with the negative input end of the operational amplifier A1 through a resistor, for example, denoted as RA; the negative input end of the operational amplifier A1 is also linked with the output end of the operational amplifier A1 through a feedback resistor RF, and the positive input end of the operational amplifier is grounded through a resistor RB; the output end of the operational amplifier A1 is connected with the input of a first audio driving module, and the output of the first audio driving module is connected with one terminal of the loudspeaker; on the other hand, the audio analog signal is directly sent to the second audio driving module, the output of the second audio driving module is connected with the other terminal of the loudspeaker, so that the loudspeaker is driven by two paths of driving signals simultaneously, as two paths of opposite-phase signals simultaneously drive the same loudspeaker, the amplitude of the signals applied to the two audio driving modules is approximately equal and the phases are opposite (according to the characteristic of virtual breaking of the operational amplifier, almost no current flows into the negative input end of the operational amplifier, so that the current of the audio analog signal driven by the current resistor RA is equal to the current of the operational amplifier driven by the signal of the output end of the operational amplifier through the current resistor RF, and in addition, the operational amplifier has the characteristic of virtual short, so that the voltage of the negative input end of the operational amplifier can be regarded as 0, and the conclusion can be obtained), meanwhile, the superposition of voltage signals can obviously appear on the 2 terminals of the loudspeaker, so that the voltage signals supplied to the loudspeaker enable the single path to be added by 2 times, and according to the relation between the voltage and the power, the operational amplifier can know: the power supplied to the loudspeaker is increased by 4 times as much as before, so that the large power output can be realized by using a smaller power supply voltage source to meet the requirement of high-power driving. (the microprocessor and the Bluetooth chip can be used for supplying power without adding a higher voltage power supply circuit)

However, in specific circuit implementation, the resistance values of the resistor RA and the resistor RF cannot be equal or infinitely approximated, in practical circuit design work, the absolute equality of the resistance values of the two resistors with the same nominal resistance value cannot be guaranteed, and sometimes a relatively large error occurs, which is obviously harmful to the design requirement of the circuit, if two resistors with exactly equal resistance values are selected through measurement, although it is feasible, we can only select to achieve the special requirement through manual measurement, which is feasible in scientific experiments, but is obviously not suitable for industrial production. Here we have further optimized the circuit: the integrated subtractor chip which is commonly used for realizing signal subtraction is selected to replace the operational amplifier A1, specifically, a conventional chip AD8276 can be selected, 4 resistors with the same resistance and good matching degree are integrated in the AD8276, the 5 th pin and the 6 th pin of the integrated subtractor chip are connected to form a feedback loop, the 1 st pin of the integrated subtractor chip is suspended, and the 3 rd pin of the integrated subtractor chip is grounded, so that a circuit formed by the resistors RA, RB, RF and the operational amplifier A1 can be replaced. The audio analog signal enters from the 2 feet of the AD8276 and is output from the 6 feet of the AD8276, and the same amplitude inversion is realized, but because the two AD8276 internal resistances replacing the resistances RA and RF are two 40K ohm resistances which are well matched (equal) through the process technology of the integrated circuit manufacturer, the problems are solved, and the actual parameters are required to be further debugged.

As shown in fig. 3, the first driving module and the second driving module designed by the invention have the same structure, and the main functions of the first driving module and the second driving module are to realize voltage amplification and current amplification so as to realize audio driving, namely, the first driving module and the second driving module are an audio driving circuit. The voltage amplification part is realized by the operational amplifier AP, the negative input end of the operational amplifier AP is connected with the output of the whole driving module through a resistor R1, the negative input end of the operational amplifier AP is grounded through a resistor R2, the voltage amplification multiple of the voltage amplification part to the audio signal is determined by the ratio of the resistor R1 to the resistor R2, the working current of the circuit is small, the heating value is small, meanwhile, the operational amplifier with small output current (within 5mA is suitable) is also selected, and the distortion phenomenon can be reduced by the operational amplifier with small output current. The current amplifying part mainly comprises transistors Q1 to Q6, the current amplifying circuit naturally hopes to have larger current output, and the current amplifying factor of the transistor capable of carrying out large current amplification is usually tens to 100; setting the current output by the operational amplifier as I1, taking the case that Q1 and Q3 are in a working state as an example, amplifying the current I1 by Q1 to obtain I2 (I2=I1.h1, h1 is the current amplification factor of Q1, and the current amplification factors of other transistors can be marked as h2, h3 and the like), sending part of I2 into the base of Q3, sending part of I2 into the base of Q5, amplifying the current respectively by Q3 and Q5, and finally sending the amplified current into a driven object loudspeaker, wherein the working processes of Q2 and Q4 in the working state are similar and are not repeated; obviously, the circuit structure can realize current step-by-step amplification to finally obtain larger output current, for the transistor, the current amplification factor of the transistor can change along with the change of collector current, and the current amplification factor of the transistor is generally changed (reduced) when the current is larger and is close to the maximum rated current, so that in order to maintain the circuit amplification factor in a stable range, the Q1 output current is divided into two parts, one part is sent to a Q3 base, and the other part is sent to a Q5 base, thereby reducing the working current of Q3 and Q5 and avoiding the working current from entering a distortion state, and meanwhile, the transistor is obviously beneficial to reducing the heating value of each transistor. Of course, the circuit can be implemented by adopting a transistor with large rated current to be matched with the structure, which relates to specific debugging of the circuit, and a resistor, a capacitor or other elements are additionally arranged in the circuit to further improve the circuit performance during specific implementation, and the circuit performance is not discussed herein.

It should be noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solution of the present invention may be modified or substituted without departing from the spirit and scope of the technical solution of the present invention, and the scope of the claims of the present invention should be covered.

Claims

1. A Bluetooth stereo system comprises a Bluetooth unit and an audio processing unit; the Bluetooth unit can realize data transmission with the audio processing unit, and is characterized in that:

the audio driving unit comprises a first driving module and a second driving module; the first driving module and the second driving module adopt the same structure, and the structure is as follows: comprises a voltage amplifying part and a current amplifying part; the voltage amplifying part comprises an operational amplifier AP; the current amplifying section includes transistors Q1 to Q6; the base electrode of the transistor Q1 is connected with the output end of the operational amplifier AP, the collector electrode of the transistor Q1 is connected with the collector electrode of the transistor Q3, the collector electrode of the transistor Q1 is also connected with the collector electrode of the transistor Q5, and the emitter electrode of the transistor Q1 is connected with the base electrode of the transistor Q3; the emitter of the transistor Q1 is also connected with the base of the transistor Q5; the emitter of the transistor Q3 and the emitter of the transistor Q5 are both connected to one terminal of the speaker; the base electrode of the transistor Q2 is connected with the output end of the operational amplifier AP, the collector electrode of the transistor Q2 is connected with the collector electrode of the transistor Q4, the collector electrode of the transistor Q2 is also connected with the collector electrode of the transistor Q6, and the emitter electrode of the transistor Q2 is connected with the base electrode of the transistor Q4; the emitter of the transistor Q2 is also connected with the base of the transistor Q6; the emitter of the transistor Q4 and the emitter connection of the transistor Q6 are both connected to one terminal of the speaker.

2. A bluetooth stereo system according to claim 1, wherein: the audio driving unit includes: the operational amplifier A1, a first driving module and a second driving module; the audio analog signal is connected with the negative input end of the operational amplifier A1 through a resistor RA; the negative input end of the operational amplifier A1 is also connected with the output end of the operational amplifier A1 through a feedback resistor RF, and the positive input end of the operational amplifier is grounded through a resistor RB; the output end of the operational amplifier A1 is connected with the input of the first driving module, and the output of the first audio driving module is connected with one terminal of the loudspeaker; the audio analog signal is directly sent to a second driving module, and the output of the second audio driving module is connected with the other terminal of the loudspeaker; the integrated subtractor chip for realizing signal subtraction is selected to replace the operational amplifier A1, the integrated subtractor chip is AD8276, 4 resistors with good matching values are integrated in the AD8276, the 5 th pin and the 6 th pin of the AD8276 chip are connected to form a feedback loop, the 1 st pin of the AD8276 chip is suspended, the 3 rd pin of the AD8276 chip is grounded, a circuit structure formed by the resistors RA, RB, RF and the operational amplifier A1 is realized, and the resistance values of the resistor RA and the resistor RF are equal.