Airborne broadcast audio power amplifier circuit

Abstract

The invention provides an airborne broadcast audio power amplifier circuit, relates to the technical field of avionic equipment, and solves the problems of low volume, audio distortion and high ground noise of the existing airborne broadcast. The power amplifier circuit comprises a digital-to-analog converter circuit, a low-pass filter circuit and a power amplifier circuit which are connected in sequence, and the digital-to-analog converter circuit receives digital audio signals from a main chip, converts the digital audio signals into analog audio signals and sends the analog audio signals to the low-pass filter circuit; the low-pass filter circuit is used for isolation and impedance input adjustment processing of analog audio signals, then the analog audio signals are sent to the power amplifier circuit, and the analog audio signals are amplified and then drive a loudspeaker to produce sound. The double-end superposition peak-to-peak value of the broadcast audio power amplifier circuit, the maximum peak voltage of the output end of the digital-to-analog converter circuit and the maximum peak voltage of the input end of the low-pass filter circuit are all determined based on rated parameters of the loudspeaker. According to the invention, the performance of the airborne loudspeaker can be further opened, so that the whole airborne broadcast audio system is improved.

Description

Technical Field

[0001] The invention relates to the technical field of avionics equipment, and is applied to the driving process of an airborne broadcast loudspeaker, in particular to an airborne broadcast audio power amplifier circuit. Background Art

[0002] In the field of avionics, the onboard broadcast audio circuit plays a key role. It receives various audio signals on the aircraft through the network, and after digital-to-analog conversion (such as using DA decoding chips) and processing by power amplifiers and other devices, it finally drives the speakers to produce sound. This system is not only responsible for transmitting the crew's speech, but also covers background music, pre-recorded broadcast information, and the playback of the in-flight entertainment system. It is an important tool to ensure effective communication between passengers and crew members.

[0003] As one of the core components of the airborne broadcast audio circuit, the airborne broadcast audio power amplifier circuit is responsible for properly amplifying the weak analog audio signal and efficiently driving the speaker to produce clear sound. This process is crucial to ensuring the broadcast quality of aviation audio electronic equipment. High-quality audio power amplifier circuit design is directly related to whether the broadcast content can be accurately conveyed to the audience, thus affecting the safety and comfort of the entire flight experience.

[0004] With the development of aviation and the advancement of technology, the design standards for aviation audio electronic equipment are also constantly improving. In order to meet the growing demand, not only is high fidelity required for audio transmission, but also good stability and reliability of the system must be ensured. However, in practical applications, existing airborne broadcast audio circuits still face some challenges and shortcomings.

[0005] The current onboard broadcast audio amplifier circuit has the problem of low broadcast volume, which limits its adaptability in different environments. Especially in large passenger aircraft or in noisy environments, low broadcast volume may result in important information not being clearly heard by all passengers. In addition, due to the peak clipping phenomenon in the audio data processing process, audio distortion occurs, which in turn affects the true reproduction of the broadcast content. On the other hand, the problem of high broadcast background noise cannot be ignored. Excessive background noise will interfere with normal broadcast content and reduce the audience's understanding and satisfaction.

[0006] In view of the above problems, it is necessary to develop an improved airborne broadcast audio power amplifier circuit to solve the deficiencies in the existing technology. The ideal solution should be able to increase the broadcast volume while reducing the background noise, and effectively avoid audio distortion to ensure the clarity and accuracy of the broadcast content. Summary of the invention

[0007] The purpose of the present invention is to solve the problems of low volume, audio distortion and high background noise in existing airborne broadcasting, and therefore an airborne broadcasting audio power amplifier circuit is proposed; the circuit design makes the broadcasting audio link match the maximum output power of the airborne speaker, avoiding the audio distortion caused by peak clipping of the audio data. Therefore, the present invention can further open up the performance of the airborne speaker, and at the same time has good circuit reliability, so that the overall performance of the airborne broadcasting audio system is improved.

[0008] The present invention adopts the following technical solutions to achieve the purpose:

[0009] An airborne broadcast audio power amplifier circuit comprises a digital-to-analog converter circuit, a low-pass filter circuit and a power amplifier circuit which are connected in sequence; the digital-to-analog converter circuit is also connected to a main chip of the airborne broadcast audio system, receives a digital audio signal from the main chip, converts the digital audio signal into an analog audio signal and then sends it to the low-pass filter circuit; the low-pass filter circuit is used for isolating the analog audio signal and adjusting the impedance input, and sends the processed analog audio signal to the power amplifier circuit; the power amplifier circuit is also connected to a loudspeaker of the airborne broadcast audio system, and amplifies the analog audio signal to drive the loudspeaker to produce sound; wherein the double-ended superimposed peak-to-peak value of the broadcast audio power amplifier circuit, the maximum peak voltage at the output end of the digital-to-analog converter circuit, and the maximum peak voltage at the input end of the low-pass filter circuit are all determined based on the rated parameters of the loudspeaker.

[0010] Specifically, the digital-to-analog converter circuit is used to isolate and individually control audio signals, and at the same time control the format, bit number, sampling rate and gain of the audio signal through its own serial interface; the analog output end of the digital-to-analog converter circuit adopts a single-ended mode and is connected to the input end of the low-pass filter circuit.

[0011] Specifically, the low-pass filter circuit is composed of an operational amplifier, which is used to provide input impedance network matching and output low-pass filtering for analog audio signals; the output end of the low-pass filter circuit is connected to the INP input end of the power amplifier in the power amplifier circuit.

[0012] Preferably, the power amplifier circuit comprises a plurality of independently configured power amplifiers, the input of each power amplifier being configured as a single-ended input and the output being configured as a BTL output.

[0013] Preferably, the power amplifier is a Class D audio amplifier, and the power amplifier is also used to provide power limiting and DC detection protection functions; the output end of each power amplifier is connected to a corresponding speaker, the INP input end of each power amplifier is connected to the output end of the low-pass filter circuit, and the INN input end of each power amplifier is coupled to the ground through a capacitor.

[0014] Specifically, the main chip of the airborne broadcast audio system is connected to each power amplifier for communication, and monitors and controls each power amplifier through Enable and Status signals.

[0015] Furthermore, the double-ended peak-to-peak value U1 of the broadcast audio power amplifier circuit is determined based on the impedance R and power P of the speaker, and is determined by the formula Determine the voltage value U of the speaker, and then determine the double-ended superimposed peak-to-peak value U1 based on the voltage value U; the low-pass filter circuit is composed of an operational amplifier with an amplification factor of A, and the power amplifier circuit has an amplification factor of B, so the amplification factor of the broadcast audio power amplifier circuit is A×B times, and the maximum peak voltage U2 at the output end of the digital-to-analog converter circuit is U1 / (A×B); in the low-pass filter circuit, the operational amplifier adopts LDO power supply mode, and the output peak voltage is U1 / B.

[0016] In summary, due to the adoption of this technical solution, the beneficial effects of the present invention are as follows:

[0017] The circuit design of the present invention takes into account the matching between the broadcast audio link and the maximum output power of the onboard speaker. By precisely adjusting the peak voltage of the power amplifier and its pre-stages, it is ensured that the audio signal can be amplified to the level that is most suitable for driving the speaker without causing audio peak clipping. This not only avoids the distortion of audio data caused by peak clipping, but also fully releases the performance potential of the speaker, so that the broadcast volume is improved, providing passengers with a clearer and more realistic listening experience.

[0018] In addition, the present invention also improves the background noise problem of the broadcast audio system. By optimizing the circuit design, the background noise is effectively reduced, achieving a low background noise effect. This improvement is crucial to improving the comprehensibility of broadcast content and the comfort of the audience. At the same time, due to the use of a simple and efficient circuit design, the reliability of the entire system is also enhanced, ensuring long-term stable operation and meeting the strict requirements for equipment reliability in the aviation environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the structure of the airborne broadcast audio power amplifier circuit of the present invention;

[0020] Figure 2 It is a connection diagram of the low-pass filter circuit in the present invention;

[0021] Figure 3 is an electrical schematic diagram of a low-pass filter circuit in the present invention;

[0022] Figure 4 is a circuit block diagram of the power amplifier in the present invention;

[0023] Figure 5It is a schematic diagram of a BTL output and a single-ended input power amplifier with power limitation in the present invention. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0025] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Example

[0027] An airborne broadcast audio power amplifier circuit, which is used to realize a low-noise, high-volume audio circuit design based on the research of audio circuits used in airborne broadcast scenarios and combined with operational amplifier circuit adjustment and other methods. In terms of hardware reliability analysis, its interface can have a fully isolated design feature, and multiple independent audio output links and speaker designs realize the transmission and partitioning functions of audio signals, ensuring the reliability of audio signals. For the transmission, reception and processing of audio signals, in addition to receiving audio signals from the airborne broadcast audio system, it also receives signal controls on its operating mode and status management. The following is a detailed introduction to the airborne broadcast audio power amplifier circuit of this embodiment.

[0028] like Figure 1 As shown, the airborne broadcast audio power amplifier circuit includes a digital-to-analog converter circuit, a low-pass filter circuit and a power amplifier circuit connected in sequence. The digital-to-analog converter circuit is also connected to the main chip of the airborne broadcast audio system, and receives the digital audio signal from the main chip, converts the digital audio signal into an analog audio signal, and then sends it to the low-pass filter circuit, thereby realizing the analogization of digital audio. The low-pass filter circuit is used for the isolation and impedance input adjustment processing of the analog audio signal (relative to the function of the power amplifier circuit), and sends the processed analog audio signal to the power amplifier circuit. The power amplifier circuit is also connected to the speaker of the airborne broadcast audio system, and amplifies the analog audio signal to drive the speaker to sound.

[0029] The key to this embodiment is that the double-ended peak-to-peak value of the broadcast audio power amplifier circuit, the maximum peak voltage at the output of the digital-to-analog converter circuit, and the maximum peak voltage at the input of the low-pass filter circuit are all determined based on the rated parameters of the speaker.

[0030] In this embodiment, the analog process of digital audio is realized based on a digital-to-analog converter circuit, which can be a DAC or DA chip, etc., which can ensure that the audio is isolated from each other and can be controlled separately, thereby providing support for subsequent partition broadcasting and other functions. The digital-to-analog converter circuit also controls the format, bit number, sampling rate and gain of the audio signal through its own serial interface, and its analog output terminal adopts a single-ended mode and is connected to the input terminal of the low-pass filter circuit.

[0031] The low-pass filter circuit connected to the output end of the digital-to-analog converter circuit is an isolated impedance input circuit established using an operational amplifier. The connection relationship diagram can be found in Figure 2 The low-pass filter circuit is used to provide input impedance network matching and output low-pass filtering of analog audio signals, and its output end is connected to the INP input end of the power amplifier in the power amplifier circuit. This design method can achieve good input impedance network matching and low-pass filtering of the output audio of the airborne broadcast audio power amplifier circuit, and reduce high-frequency interference of the output audio. The specific electrical principle diagram of the low-pass filter circuit can be found in Figure 3 .

[0032] As a preferred embodiment of the present invention, the power amplifier circuit includes a plurality of independently configured power amplifiers, the input of each power amplifier is configured as a single-ended input, and the output is configured as a BTL output. In the single-ended input case of the present embodiment, the power amplifier has only one positive phase input INP, and the negative phase input INN is grounded or connected to a fixed reference voltage; therefore, in the present embodiment, the output of each power amplifier is connected to a corresponding speaker, the INP input of each power amplifier is connected to the output of the low-pass filter circuit, and the INN input of each power amplifier is coupled to the ground through a capacitor.

[0033] Since each power amplifier is relatively independent, each audio input can drive the speaker to achieve audio amplification and output effects, which allows the zoned playback requirements of airborne broadcasting.

[0034] As for the bridge-tied load (BTL) output of the power amplifier, it is a special output configuration that uses two amplifier channels to drive the same speaker load. The speaker actually feels the difference between the two channel outputs. In theory, it can achieve advantages such as twice the output voltage swing and four times the power compared to single-ended output. The power amplifier configuration of this embodiment can significantly improve the output capacity without changing the input signal source, and because the BTL output does not require load grounding, it can reduce the impact of interference and noise, and can also more effectively utilize the voltage range provided by the power supply. The circuit diagram of the TL output and single-ended input power amplifier with power limitation can be found in Figure 5 .

[0035] The power amplifier used in this embodiment is a Class D audio amplifier with SpeakerGuard TM Functions include Power Limiter and DC Detection; this feature enables it to have excellent EMI suppression performance and meet the requirements of electromagnetic compatibility (EMC). It also has short circuit protection, thermal protection and automatic recovery functions.

[0036] Class D audio amplifiers are becoming more and more popular in modern audio systems due to their high efficiency and small size, especially in applications with strict requirements on efficiency and heat dissipation, such as airborne broadcast systems. Unlike traditional analog Class A, Class B or Class AB amplifiers, Class D audio amplifiers convert input analog audio signals into high-frequency switching signals through pulse width modulation or pulse frequency modulation technology. These switching signals are amplified and converted back into analog signals through internal low-pass filtering to drive speakers. This working mode enables it to achieve an efficiency of less than 90% in theory, which is much higher than traditional linear amplifiers and is suitable for use in the airborne broadcast audio amplifier circuit of this embodiment.

[0037] Combination Figure 1 and Figure 4 As shown in the figure, the main chip of the airborne broadcast audio system is connected to each power amplifier for communication, and monitors and controls each power amplifier through Enable and Status signals, which correspond to the operation mode and status management of the power amplifier.

[0038] In this embodiment, the main chip of the airborne broadcast audio system is also connected to the power amplifier circuit through the power amplifier power supply circuit. The power amplifier power supply circuit is configured with an I2C-TTL conversion circuit for reading the status of each power amplifier and controlling the on and off of each power amplifier; the IO port of the main chip is directly connected to the SDA and SCL interfaces of the I2C-TTL conversion circuit, and the main chip performs serial-to-parallel conversion of data by controlling the I2C timing, thereby monitoring multiple power amplifiers.

[0039] As a preferred embodiment of this embodiment, Figure 1 As shown, the power amplifier circuit is connected to the speaker of the airborne broadcast audio system through an EMI filter circuit. The EMI filter circuit is used to protect the amplified analog audio signal from electromagnetic interference. The EMI filter circuit is implemented in the form of a ferrite bead filter circuit and is equipped with a common-mode choke.

[0040] The EMI filter circuit itself can effectively reduce electromagnetic interference from the external environment or the system, thereby ensuring the quality of the audio signal. In terms of electromagnetic compatibility, it ensures that the corresponding circuit will neither become a source of interference for other circuits or components nor be interfered with by other circuit components; the EMI filter circuit can also prevent high-frequency noise or other types of interference from leaving the power amplifier and affecting the performance of subsequent speakers. The ferrite bead filter circuit used in the EMI filter circuit of this embodiment, in which the ferrite bead is a component that absorbs the energy of high-frequency noise by utilizing the high magnetic permeability of the material and converts it into heat dissipation, which can effectively attenuate unwanted high-frequency components while having little effect on low-frequency audio signals. The common mode choke CMC is a dual-winding inductor specially designed to block common-mode noise while allowing differential-mode signals (i.e., the required audio signals) to pass smoothly. When the EMI filter circuit is applied to the airborne broadcast audio power amplifier circuit, the stability and sound quality of the airborne broadcast audio system can be significantly improved, ensuring clear and interference-free sound output in various environments.

[0041] In this embodiment, Figure 1 As shown, a lightning protection circuit is also provided between the EMI filter circuit and the loudspeaker of the airborne broadcast audio system. The lightning protection circuit performs lightning protection on the analog audio signal after EMI filtering through a TVS diode. The clamping voltage of the TVS diode is higher than the peak voltage of the loudspeaker by a preset threshold value. The TVS diode is connected in parallel to the output end of the EMI filter circuit to achieve lightning protection and ESD protection.

[0042] The following is a detailed introduction to the circuit design process for matching the voltage peak values ​​of each level of the audio link based on the rated parameters of the loudspeaker in the power amplifier circuit of this embodiment.

[0043] According to the formula Where U1 is the peak-to-peak value of the double-ended superimposed signal of the broadcast audio power amplifier circuit. The rated parameters of the speaker (including impedance R and power P) can be calculated: when the broadcast audio power amplifier circuit drives the speaker to achieve the maximum power of the speaker, the peak-to-peak value of the double-ended superimposed signal of the broadcast audio power amplifier circuit U1 and the peak-to-peak value of the single-ended voltage V pp =U1 / 2.

[0044] In the airborne broadcast audio power amplifier circuit, the low-pass filter circuit is composed of an operational amplifier with an amplification factor of A, and the amplification factor of the power amplifier circuit is B. Therefore, the amplification factor of the airborne broadcast audio power amplifier circuit is A×B times. When the maximum peak voltage U2 output by the digital-to-analog converter circuit is about U1 / (A×B), the maximum power output of the speaker can be achieved.

[0045] In the low-pass filter circuit, when the operational amplifier outputs an analog audio signal to the power amplifier circuit for amplification, the amplifier's amplification factor is B. However, when the operational amplifier outputs a small signal, the signal-to-noise ratio is not high due to the overly large reference voltage, which will eventually increase the background noise of the audio output. Therefore, the operational amplifier uses LDO power supply to make the ripple smaller, and the peak voltage at the output of the operational amplifier is U1 / B, so that the input audio peak voltage of the airborne broadcast audio power amplifier circuit is also U1 / B.

[0046] In summary, this embodiment is aimed at the airborne broadcast audio power amplifier circuit, based on the performance openness of the speaker and the broadcast requirements of high volume and low noise floor, and proposes a circuit design for matching the voltage peaks of each level of the audio link based on the rated parameters of the speaker. When using the power amplifier circuit of this embodiment, by adjusting the peak voltage of the power amplifier and its pre-stages, the maximum output power of the speaker can be matched without causing peak clipping, thereby avoiding the audio distortion caused by peak clipping, increasing the speaker volume, and alleviating the problem of high noise floor.

Claims

1. An airborne broadcast audio power amplifier circuit, characterized in that: It includes a digital-to-analog converter circuit, a low-pass filter circuit and a power amplifier circuit connected in sequence; the digital-to-analog converter circuit is also connected to the main chip of the airborne broadcast audio system, and receives the digital audio signal from the main chip, converts the digital audio signal into an analog audio signal and sends it to the low-pass filter circuit; the low-pass filter circuit is used for isolating the analog audio signal and adjusting the impedance input, and sends the processed analog audio signal to the power amplifier circuit; the power amplifier circuit is also connected to the speaker of the airborne broadcast audio system, and amplifies the analog audio signal to drive the speaker to make sound; wherein, the double-ended superimposed peak-to-peak value of the broadcast audio power amplifier circuit, the maximum peak voltage at the output end of the digital-to-analog converter circuit, and the maximum peak voltage at the input end of the low-pass filter circuit are all determined based on the rated parameters of the speaker.

2. The airborne broadcast audio power amplifier circuit according to claim 1, characterized in that: The digital-to-analog converter circuit is used for mutual isolation and individual control of audio signals, and at the same time controls the format, bit number, sampling rate and gain of the audio signal through its own serial interface; the analog output end of the digital-to-analog converter circuit adopts a single-ended mode and is connected to the input end of the low-pass filter circuit.

3. The airborne broadcast audio power amplifier circuit according to claim 1, characterized in that: The low-pass filter circuit is composed of an operational amplifier and is used to provide input impedance network matching and output low-pass filtering of analog audio signals; the output end of the low-pass filter circuit is connected to the INP input end of the power amplifier in the power amplifier circuit.

4. The airborne broadcast audio power amplifier circuit according to claim 1, characterized in that: The power amplifier circuit includes a plurality of independently configured power amplifiers, wherein the input of each power amplifier is configured as a single-ended input and the output is configured as a BTL output.

5. The airborne broadcast audio power amplifier circuit according to claim 4, characterized in that: The power amplifier is a Class D audio power amplifier, and is also used to provide power limitation and DC detection protection functions; the output end of each power amplifier is connected to a corresponding speaker, the INP input end of each power amplifier is connected to the output end of the low-pass filter circuit, and the INN input end of each power amplifier is coupled to the ground through a capacitor.

6. The airborne broadcast audio power amplifier circuit according to claim 4, characterized in that: The main chip of the airborne broadcast audio system is connected to each power amplifier and monitors and controls each power amplifier through Enable and Status signals.

7. The airborne broadcast audio power amplifier circuit according to claim 6, characterized in that: The main chip of the airborne broadcast audio system is also connected to the power amplifier circuit through the power amplifier power supply circuit. The power amplifier power supply circuit is equipped with an I2C-TTL conversion circuit for reading the status of each power amplifier and controlling the opening and closing of each power amplifier; the IO port of the main chip is directly connected to the SDA and SCL interfaces of the I2C-TTL conversion circuit. The main chip performs serial-to-parallel conversion of data by controlling the I2C timing, thereby monitoring multiple power amplifiers.

8. The airborne broadcast audio power amplifier circuit according to claim 1, characterized in that: The power amplifier circuit is connected to the speaker of the airborne broadcast audio system through an EMI filter circuit. The EMI filter circuit is used to protect the amplified analog audio signal from electromagnetic interference. The EMI filter circuit is implemented in the form of a ferrite bead filter circuit and is equipped with a common-mode choke.

9. The airborne broadcast audio power amplifier circuit according to claim 8, characterized in that: A lightning protection circuit is also provided between the EMI filter circuit and the loudspeaker of the airborne broadcast audio system. The lightning protection circuit performs lightning protection on the analog audio signal after EMI filtering through a TVS diode. The clamping voltage of the TVS diode is higher than the peak voltage of the loudspeaker by a preset threshold value. The TVS diode is connected in parallel to the output end of the EMI filter circuit to achieve lightning protection and ESD protection.

10. The airborne broadcast audio power amplifier circuit according to claim 1, characterized in that: The double-ended peak-to-peak value U1 of the broadcast audio power amplifier circuit is determined based on the impedance R and power P of the speaker, and is determined by the formula Determine the voltage value U of the speaker, and then determine the double-ended superimposed peak-to-peak value U1 based on the voltage value U; the low-pass filter circuit is composed of an operational amplifier with an amplification factor of A, and the power amplifier circuit has an amplification factor of B, so the amplification factor of the broadcast audio power amplifier circuit is A×B times, and the maximum peak voltage U2 at the output end of the digital-to-analog converter circuit is U1 / (A×B); in the low-pass filter circuit, the operational amplifier adopts LDO power supply mode, and the output peak voltage is U1 / B.

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