A car cabin class-D power amplifier output multi-path mixing sound recovery denoising circuit and a vehicle-mounted audio system
By combining an LC filter module, an RC filter op-amp follower module, and a mixing output filter module, the problems of inflexible hardware circuit adaptation and increased cost of multiple outputs are solved, achieving low-cost and flexible multi-channel voice echo noise reduction and improving the voice recognition rate.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- HENAN TIANMAI TECH CO LTD
- Filing Date
- 2025-06-12
- Publication Date
- 2026-06-16
AI Technical Summary
In existing technologies, echo cancellation based on pure software algorithms suffers from latency issues, lacks flexible hardware circuit adaptation, and requires additional circuitry for multi-output and multi-zone applications, leading to increased costs.
A combined circuit consisting of an LC filter module, an RC filter operational amplifier follower module, and a mixing output filter module, including inductors, capacitors, resistors, and operational amplifiers, is used to achieve real-time noise reduction of multiple signals through filtering and signal coupling.
It achieves low-cost, flexible multi-channel, multi-zone speech echo noise reduction, improves speech recognition rate, and solves the latency problem of pure software algorithms and the problem of inflexible hardware circuit adaptation.
Smart Images
Figure CN224367957U_ABST
Abstract
Description
Technical Field
[0001] This utility model belongs to the field of audio noise reduction technology, specifically relating to a multi-channel mixing and noise reduction circuit for Class D power amplifier output in a car cabin and an in-vehicle audio system. Background Technology
[0002] Voice recognition is now an essential feature in modern car cockpit systems. However, voice recognition rates are significantly affected by ambient noise, including but not limited to engine noise, wind noise, air conditioning noise, and passenger conversations. Additionally, there is echo interference from speaker playback (such as navigation and music). To improve voice recognition rates, echo cancellation is typically performed, removing the reference signal component from the microphone signal to avoid self-interference, such as navigation voice being mistakenly recorded as commands.
[0003] Class D amplifiers output high-frequency square waves, which carry audio information via PWM. These square waves contain a large number of high-frequency harmonics, far exceeding the audio range. Direct sampling will cause high-frequency noise to be mixed in, which will contaminate the audio frequency band and pollute the sampled signal, making it impossible to sample directly.
[0004] Currently, echo cancellation mainly combines noise suppression (ANS) algorithms to separate the target human voice from background noise and improve the quality of the speech signal. However, current implementations are generally based on pure software algorithms, which suffer from latency issues. This latency is not fixed and is difficult to completely eliminate through algorithmic optimization. To address this problem, echo cancellation can also be performed by directly sampling the sound output from the vehicle's own speakers to avoid latency and distortion. However, existing hardware circuits are not flexible enough, and additional circuitry is often required for multi-output and multi-zone systems, increasing costs. Utility Model Content
[0005] To address the shortcomings and problems of current echo cancellation based on pure software algorithms, such as time delay and inflexible adaptation of existing hardware circuits, as well as the increased cost due to the need for additional circuitry for multi-channel output and multi-zone audio, this utility model provides a multi-channel mixing echo cancellation circuit for Class D power amplifier output in automotive cockpits and an in-vehicle audio system.
[0006] This invention provides a multi-channel mixing and noise reduction circuit for Class D power amplifier output in an automotive cockpit, including an LC filter module, an RC filter operational amplifier follower module, and a mixing output filter module.
[0007] The LC filter module is used to filter out the modulated fundamental frequency component of the Class D power amplifier, and includes at least two first-order LC filter units connected in series at the output of the power amplifier.
[0008] The input terminal of the RC filter operational amplifier follower module is connected to the output terminal of the LC filter module, and includes at least two sets of RC filter operational amplifier follower units connected to two sets of first-order LC filter units respectively. The RC filter operational amplifier follower unit includes a DC blocking capacitor, a resistor voltage divider unit, a first-order RC low-pass filter and an operational amplifier follower circuit connected in series. The input terminal of the DC blocking capacitor is connected to the output terminal of the corresponding first-order LC filter unit and is used to adjust the attenuation ratio and the cutoff frequency threshold of the RC low-pass filter.
[0009] The input terminal of the mixing output filter module is connected to the output terminal of the RC filter operational amplifier follower module, and includes a voltage divider resistor network, an RC low-pass filter and a coupling output capacitor, which are used to mix the multiple outputs of the RC filter operational amplifier follower module into a single signal output.
[0010] The aforementioned automotive cockpit Class D power amplifier output multi-channel mixing and noise reduction circuit, wherein the RC filter operational amplifier follower unit further includes a DC blocking capacitor connected in series between the first-order RC low-pass filter and the operational amplifier follower circuit.
[0011] The aforementioned automotive cockpit Class D power amplifier output multi-channel mixing and noise reduction circuit includes an RC filter operational amplifier follower module that further comprises multiple output capacitors. One end of each output capacitor is connected to the output terminal of the corresponding operational amplifier follower circuit, and the other end is connected to the input terminal of the mixing output filter module.
[0012] The aforementioned automotive cockpit Class D power amplifier output multi-channel mixing and noise reduction circuit uses a single power supply mode for the operational amplifier follower circuit. The power supply terminal is connected to a 5V power supply, and the reference voltage source VREF_2V5 provides a midpoint bias for the operational amplifier, enabling the signal to be transmitted within the range of 0~5V.
[0013] In the aforementioned automotive cockpit Class D power amplifier output multi-channel mixing and noise reduction circuit, the voltage divider resistor unit and the RC low-pass filter in the mixing output filter module share a common multiplexed resistor. One end of the multiplexed resistor is connected to the junction node of the multiple output capacitors in the RC filter operational amplifier follower module, and the other end is connected to the input terminal of the coupling output capacitor. This end is also connected in series with the voltage divider resistor and then grounded. The grounding capacitor is connected in parallel across the two ends of the voltage divider resistor branch to form the RC low-pass filter.
[0014] This utility model also provides an in-vehicle audio system, including the multi-channel mixing and noise reduction circuit for Class D power amplifier output in the car cabin as described in any one of the above, for processing the output signal of the multi-zone Class D power amplifier in the cabin to achieve audio sampling and noise reduction.
[0015] Compared with the prior art, the beneficial effects of this utility model are:
[0016] 1. The LC filter module of this utility model uses an inductor and a GND capacitor to filter out the modulated fundamental frequency component of the Class D power amplifier and restore the true analog sound signal; the RC filter op-amp follower module adjusts the attenuation ratio and the cutoff frequency threshold of the RC low-pass filter, and the op-amp follower circuit ensures that the output has sufficient driving capability; the mixing output filter circuit adopts a coupling capacitor plus RC filter design, so that multiple outputs are coupled and mixed into one signal output through a capacitor; at the same time, the mixing output filter module has a multiplexed resistor, which participates in voltage division attenuation with the voltage divider resistor and forms an RC filter with the filter capacitor, simplifying components and reducing costs; this circuit can achieve low cost; this circuit can realize real-time feedback of multi-channel, multi-zone Class D power amplifier output, and the circuit is flexible and can be adapted to the output of all Class D power amplifiers, improving the accuracy of voice echo cancellation and voice recognition rate.
[0017] 2. This utility model is a mixing circuit with multiple Class D power amplifier outputs built by inductors, resistors, capacitors and operational amplifiers. It is low in cost, highly flexible, suitable for real-time back sampling, improves voice recognition rate, and can make up for the lack of back sampling analog channel resources and the time delay problem of pure soft back sampling. Attached Figure Description
[0018] Figure 1 This is a schematic diagram of the structure of the Class D power amplifier output multi-channel mixing and noise reduction circuit of this utility model.
[0019] Figure 2 This is a circuit diagram of the Class D power amplifier output multi-channel mixing and noise reduction circuit of this utility model. Detailed Implementation
[0020] To address the shortcomings and problems of current echo cancellation methods based on pure software algorithms, such as time delays and inflexible hardware circuit adaptation, as well as the increased cost due to the need for additional circuitry for multi-output and multi-zone features, this invention provides a multi-channel mixing echo cancellation circuit for Class D power amplifiers in automotive cockpits. The invention will be further described and illustrated below with reference to the accompanying drawings and specific embodiments.
[0021] Example: This example provides a multi-channel mixing and noise reduction circuit for Class D power amplifier output in automotive cockpits. This circuit can be widely used in automotive cockpit domain control, in-vehicle central control, and other products. Its structural schematic diagram is shown below. Figure 1 As shown, the circuit includes an LC filter module, an RC filter operational amplifier follower module, and a mixer output filter module. The LC filter module includes at least two sets of first-order LC filter units connected in series at the power amplifier output, such as... Figure 2As shown, L1 is connected in series with INPUT1, one end of C4 is connected to the connection point between L1 and the subsequent stage, and the other end is grounded. L2 is connected in series with INPUT2, one end of C11 is connected to the connection point between L2 and the subsequent stage, and the other end is grounded. Inductor L1 and ground-filtering capacitor C4, as well as inductor L2 and ground-filtering capacitor C11, respectively constitute a first-order LC filter. The cutoff frequency is calculated using the formula fc=1 / 2πLC. L1+C4 and L2+C11 respectively process the Class D amplifier output of the left and right channels (or front and rear sound zones) to ensure independent filtering of multiple signals. This LC filter module uses an inductor and a GND capacitor to block the high-frequency components of the Class D amplifier's PWM switch, filter out the modulation fundamental frequency components of the Class D amplifier, and restore the real analog sound signal.
[0022] The input of the RC filter op-amp follower module is connected to the output of the LC filter module, used to adjust the attenuation ratio and the cutoff frequency threshold of the RC low-pass filter. The RC filter op-amp follower module includes at least two sets of RC filter op-amp follower units connected to the two sets of LC filter units. Each filter op-amp follower unit includes a DC blocking capacitor, a voltage divider resistor unit, a first-order RC low-pass filter, an op-amp follower circuit, and an output capacitor connected in series. Figure 2 As shown, DC blocking capacitors C3 and C7 filter out the DC component at the input, and their inputs are connected to the two outputs of the two first-order LC filter units, respectively. Voltage divider resistors R1, R3, R7, and R10 form a resistor voltage divider. This resistor-based voltage divider prevents excessive input signal amplitude from causing saturation or distortion in subsequent circuits, allowing for flexible adjustment of the signal attenuation ratio to suit the output amplitude requirements of different Class D power amplifiers. Resistor R2 and grounding capacitor C5, and resistor R8 and grounding capacitor C12 form a first-order RC low-pass filter. The cutoff frequency is calculated using the formula fc = 1 / 2πRC, suppressing residual switching noise and ultrasonic interference from the Class D power amplifier. U1A, resistor R4, and U1B, resistor R11 form an operational amplifier follower circuit to increase output drive capability. R4 and R11 are feedback resistors to ensure stable circuit operation. The output of U1A (pin 1) is connected in series with the output DC blocking capacitor C2, and the output of U1B (pin 7) is connected in series with the output DC blocking capacitor C2. The R5 pin is connected in series with the output DC blocking capacitor C8. The two output DC blocking capacitors C2 and C8 converge at the same node, that is, the front end of R5 is connected to the input terminal of the mixing output filter module.
[0023] The mixing output filtering module includes a voltage divider resistor network (R5, R6, R9), an RC low-pass filter (R5, C9), and a coupling output capacitor C6. One end of the multiplexing resistor R5 is connected to the junction of output capacitors C2 and C8 to isolate DC, avoiding crosstalk between channels by receiving audio signals from different paths. The other end of R5 is connected to the coupling output capacitor C6 and then to the final output OUTPUT terminal of the subsequent signal path. This end is also grounded through resistor R6 in series with R9. The grounding capacitor C9 is connected in parallel across the R6 / R9 branch to form an RC low-pass filter. R5 plays a role in both the voltage divider resistor network and the RC low-pass filter. Specifically, on one hand, the other end of R5 is connected to the voltage divider resistors R6 and R9 to form a resistor voltage divider circuit. The lower end of R6 is connected in series with R9 and then grounded. The mixed signal is uniformly attenuated by the resistor ratio. This attenuation is a global attenuation function, flexibly adjusting the total amplitude of the mixed signal. On the other hand, the other end of R5 is connected to the grounding capacitor C9 to form an RC low-pass filter circuit. Connected in parallel to the voltage divider resistors R6 / R9, with one end connected to the R6 / R9 connection point and the other end grounded, it can further suppress residual high-frequency noise, filter closer to the acquisition end, and optimize signal purity. After the two output DC blocking capacitors C2 and C8 are output, they are finally mixed into one signal through the coupling output capacitor C6 and output through the OUTPUT terminal, ensuring that the output signal meets the ADC acquisition requirements. In this mixing output filtering module, R5 participates in voltage division attenuation with R6 and R9, and also forms an RC filter with C9, which can simplify components and reduce costs.
[0024] This invention's LC filter module uses an inductor and a GND capacitor to filter out the modulated fundamental frequency component of the Class D power amplifier, restoring the true analog sound signal. The RC filter operational amplifier follower module adjusts the attenuation ratio and the cutoff frequency threshold of the RC low-pass filter, with the operational amplifier follower circuit ensuring sufficient drive capability for the output. The mixing output filter circuit uses a coupling capacitor and RC filter design, allowing multiple outputs to be coupled and mixed into a single signal output through a single capacitor. This circuit, built with inductors, resistors, capacitors, and operational amplifiers, provides a multi-channel Class D power amplifier output mixing circuit, enabling low-cost real-time re-import of multi-channel, multi-range Class D power amplifier outputs. The circuit is flexible and adaptable to the outputs of all Class D power amplifiers, improving the accuracy of voice echo cancellation and voice recognition, and compensating for insufficient analog re-import resources and the latency issues of pure soft re-import.
[0025] The above description is only a preferred embodiment of the present utility model and does not limit the present utility model. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.
Claims
1. A multi-channel mixing and noise reduction circuit for Class D power amplifier output in automotive cockpits, characterized in that: It includes an LC filter module, an RC filter op-amp follower module, and a mixing output filter module; The LC filter module is used to filter out the modulated fundamental frequency component of the Class D power amplifier, and includes at least two first-order LC filter units connected in series at the output of the power amplifier. The input terminal of the RC filter operational amplifier follower module is connected to the output terminal of the LC filter module, and is used to adjust the attenuation ratio and the cutoff frequency threshold of the RC low-pass filter. It includes at least two sets of RC filter operational amplifier follower units connected to two sets of first-order LC filter units respectively. The RC filter operational amplifier follower unit includes a DC blocking capacitor, a resistor voltage divider unit, a first-order RC low-pass filter and an operational amplifier follower circuit connected in series. The input terminal of the DC blocking capacitor is connected to the output terminal of the corresponding first-order LC filter unit. The input terminal of the mixing output filter module is connected to the output terminal of the RC filter operational amplifier follower module, and includes a voltage divider resistor network, an RC low-pass filter and a coupling output capacitor, which are used to mix the multiple outputs of the RC filter operational amplifier follower module into a single signal output.
2. The automotive cockpit Class D power amplifier output multi-channel mixing and noise reduction circuit according to claim 1, characterized in that: The RC filter operational amplifier follower unit also includes a DC blocking capacitor connected in series between the first-order RC low-pass filter and the operational amplifier follower circuit.
3. The automotive cockpit Class D power amplifier output multi-channel mixing and noise reduction circuit according to claim 1, characterized in that: The RC filter operational amplifier follower module also includes multiple output capacitors, one end of which is connected to the output terminal of the corresponding operational amplifier follower circuit, and the other end is connected to the input terminal of the mixing output filter module.
4. The automotive cockpit Class D power amplifier output multi-channel mixing and noise reduction circuit according to claim 1, characterized in that: The operational amplifier follower circuit adopts a single power supply mode, with the power supply terminal connected to a 5V power supply. The reference voltage source VREF_2V5 provides a midpoint bias for the operational amplifier, enabling the signal to be transmitted in the range of 0~5V.
5. The automotive cockpit Class D power amplifier output multi-channel mixing and noise reduction circuit according to claim 3, characterized in that: In the mixing output filtering module, the voltage divider resistor unit and the RC low-pass filter share a common multiplexing resistor. One end of the multiplexing resistor is connected to the junction node of the multiple output capacitors in the RC filter operational amplifier follower module, and the other end is connected to the input terminal of the coupling output capacitor. This end is also connected in series with the voltage divider resistor and then grounded. The grounding capacitor is connected in parallel across the two ends of the voltage divider resistor branch to form the RC low-pass filter.
6. A vehicle-mounted audio system, characterized in that, The invention includes the multi-channel mixing and noise reduction circuit for Class D power amplifier output in automotive cockpits as described in any one of claims 1-5, used to process the output signals of Class D power amplifiers in multi-zone cockpits to achieve audio sampling and noise reduction.