Audio decoding output stage circuit and audio equipment

Abstract

The invention relates to an audio decoding output stage circuit and audio equipment, the audio decoding output stage circuit comprises an I / V conversion module and a low-pass filtering module, and the I / V conversion module comprises a conversion circuit, a crossed diamond amplification circuit, an overcurrent protection circuit and a Roche network circuit; the conversion circuit comprises a JFET (Junction Field Effect Transistor) audio operational amplifier chip and an I / V (Input / Output) conversion resistor and is used for converting an input current into an analog voltage signal; the crossed diamond amplifying circuit can reduce the input offset voltage; the over-current protection circuit can carry out over-current protection; the rowbell network circuit can prevent high-frequency self-oscillation of the power output stage; and the low-pass filtering module comprises a filtering circuit and an ultrahigh frequency filtering circuit arranged at the output end of the audio decoding output stage circuit. The scheme can bring high-performance sound performance, and has the advantages of lower distortion, higher conversion rate, low output impedance and large pushing current.

Description

Technical Field

[0001] This invention relates to the field of audio device circuit technology, and in particular to an audio decoding output stage circuit and an audio device. Background Technology

[0002] Existing Hi-Fi digital audio devices, such as CD players, audio decoders, and network players, mostly incorporate high-performance, high-specification decoding chips (DAC digital-to-analog converters) to achieve high-fidelity sound quality. Many high-performance audio DACs have current outputs, which must be converted to voltage outputs to be used with audio amplifiers. In Hi-Fi audio applications, ensuring that the DAC's signal-to-noise ratio and total harmonic distortion plus noise performance are not affected by the current-voltage output stage is crucial. The current-voltage output stage and low-pass filter (LPF) connected to the DAC chip's analog signal output will depend on the audio device's performance parameters and perceived sound quality. Due to cost or manufacturing process constraints, some audio device current-output DAC chips use operational amplifiers (op-amps) for current-to-voltage conversion. Furthermore, some modern audio DACs output relatively large currents; for example, a commonly used eight-channel audio DAC outputs 15mA Vpp per pin, resulting in a total output of 120mA Vpp for eight pins connected in parallel. Using a single op-amp for current-to-voltage conversion would place a heavy load on the op-amp, potentially causing it to overheat and burn out, and severely degrading overall electrical performance parameters (such as THD, noise floor, and linearity). While multiple op-amps can be combined in parallel, this method requires a significantly larger number of op-amps, increasing material costs and complicating manufacturing and debugging processes. Summary of the Invention

[0003] Based on this, it is necessary to address the problems of poor output linearity and complex manufacturing processes in existing audio circuits. On one hand, this invention provides an audio decoding output stage circuit, including an electrically connected I / V conversion module and a low-pass filter module. The I / V conversion module includes a conversion circuit, a cross-type diamond amplifier circuit, an overcurrent protection circuit, and a Joubert network circuit. The conversion circuit includes a JFET audio operational amplifier chip and an I / V conversion resistor to convert the input current into an analog voltage signal. The input terminal of the cross-type diamond amplifier circuit is connected to the output terminal of the conversion circuit to reduce the input offset voltage. The input terminal of the overcurrent protection circuit is connected to the output terminal of the cross-type diamond amplifier circuit for overcurrent protection. The Joubert network circuit is located at the output terminal of the I / V conversion module to prevent high-frequency self-oscillation of the power output stage. The low-pass filter module includes a filter circuit and an ultra-high frequency filter circuit located at the output terminal of the audio decoding output stage circuit.

[0004] On the other hand, the present invention also proposes an audio device, including a decoding chip and an audio decoding output stage circuit as described above.

[0005] This technical solution proposes an audio decoding output stage circuit and audio device for high-current output audio DACs, specifically for N-conversion and differential synthesis output. The amplifier circuit utilizes a buffer circuit composed of operational amplifiers, reducing the number of components. It is suitable for the receiving end of multi-channel output DACs, including current-output Hi-Fi audio DAC chips. The circuit delivers high-performance sound with advantages such as lower distortion, higher slew rate, low output impedance, and high drive current, effectively meeting the listening needs of music lovers. Attached Figure Description

[0006] Figure 1 This is a schematic diagram of a module of an embodiment of the audio decoding output stage circuit proposed in this invention;

[0007] Figure 2 This is a circuit diagram of the I / V conversion module of an embodiment of the audio decoding output stage circuit proposed in this invention;

[0008] Figure 3 This is a circuit diagram of a low-pass filter module in an embodiment of the audio decoding output stage circuit proposed in this invention.

[0009] The attached diagram lists the components represented by each number as follows:

[0010] 10. Decoding chip; 20. Conversion circuit; 30. Cross-type diamond amplifier circuit; 40. Overcurrent protection circuit; 50. Jobel network circuit; 60. Filtering circuit; 70. Ultra-high frequency filtering circuit. Detailed Implementation

[0011] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the specific details described below are only a part of the embodiments of the present invention, and the present invention can be implemented in many other embodiments different from those described herein. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0012] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly attached to the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0013] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0014] In one embodiment, please refer to Figures 1 to 3 As shown, an audio decoding output stage circuit includes an I / V conversion module and a low-pass filter module electrically connected. The I / V conversion module includes a conversion circuit 20, a cross-type diamond amplifier circuit 30, an overcurrent protection circuit 40, and a Joubert network circuit 50. The conversion circuit 20 includes a JFET audio operational amplifier chip and an I / V conversion resistor to convert the input current into an analog voltage signal. The input terminal of the cross-type diamond amplifier circuit 30 is connected to the output terminal of the conversion circuit 20 to reduce the input offset voltage. The input terminal of the overcurrent protection circuit 40 is connected to the output terminal of the cross-type diamond amplifier circuit 30 for overcurrent protection. The Joubert network circuit 50 is disposed at the output terminal of the I / V conversion module to prevent high-frequency self-oscillation of the power output stage. The low-pass filter module includes a filter circuit 60 and an ultra-high frequency filter circuit 70 disposed at the output terminal of the audio decoding output stage circuit.

[0015] In this embodiment, the conversion circuit 20 includes a JFET audio operational amplifier chip, a fifth resistor, and a ninth capacitor. The first end of the fifth resistor is connected to the signal input terminal of the JFET audio operational amplifier chip, and the ninth capacitor is connected in parallel across the fifth resistor.

[0016] Based on this embodiment, the cross-type diamond amplifier circuit 30 includes a fourth switch, a sixth switch, a seventh switch, and a tenth switch. The sixth and seventh switches are both twins. The controlled terminals of the sixth and seventh switches are connected to the output terminals of the conversion circuit 20, and their output terminals are connected to a power supply. The sixth and seventh switches are also connected to the controlled terminals of the fourth and tenth switches, respectively. It further includes a second constant current source circuit, which includes a third switch, a ninth switch, a seventh resistor, a second resistor, a third resistor, an eighteenth resistor, and a nineteenth resistor. The second and third resistors are respectively positioned between the two input terminals of the third switch and the power supply. The first output terminal of the third switch is connected to the input terminal of the sixth switch. The eighteenth and nineteenth resistors are respectively positioned between the two input terminals of the ninth switch and the power supply. The first output terminal of the ninth switch is connected to the input terminal of the seventh switch, and the other output terminal of the third switch is connected to the other output terminal of the ninth switch via the seventh resistor.

[0017] The overcurrent protection circuit 40 includes a fifth switch and an eighth switch; the controlled terminal of the fifth switch is connected to the output terminal of the fourth switch, and the input terminal of the fifth switch is connected to the controlled terminal of the fourth switch; the controlled terminal of the eighth switch is connected to the output terminal of the tenth switch, and the input terminal of the eighth switch is connected to the controlled terminal of the tenth switch.

[0018] Furthermore, the conversion circuit 20 also includes a first constant current source circuit, which provides a constant operating current to the output stage of the JFET audio operational amplifier chip. The first constant current source circuit includes a first switching transistor, a second switching transistor, a first resistor, and a sixth resistor. The input terminal of the first switching transistor is connected to a power supply, and the first switching transistor is grounded through the sixth resistor. The first resistor is connected in parallel between the input terminal and the controlled terminal of the first switching transistor. The controlled terminal of the second switching transistor is connected to the output terminal of the first switching transistor, the input of the second switching transistor is connected to the controlled terminal of the first switching transistor, and the output terminal of the second switching transistor is connected to the current terminal of the JFET audio operational amplifier chip.

[0019] In this embodiment, the ultra-high frequency filtering circuit 70 includes a sixteenth resistor and a fifth capacitor connected in parallel, and the output terminal of the audio decoding output stage circuit is grounded through the ultra-high frequency filtering circuit 70.

[0020] In this invention, the Joubert network circuit 50 includes a sixteenth resistor and a fifth capacitor, and the output terminal of the I / V conversion module is grounded through the sixteenth resistor and the fifth capacitor in sequence.

[0021] On the other hand, the present invention also proposes an audio device, including a decoding chip 10 and the audio decoding output stage circuit described above.

[0022] This technical solution proposes an audio decoding output stage circuit and audio device for the N-conversion and differential synthesis output of high-current output audio DACs. The amplifier circuit uses a buffer circuit composed of operational amplifiers, reducing the number of components. It is suitable for the receiving end of multi-channel output DACs, including current-output Hi-Fi audio DAC chips. Its circuit delivers high-performance sound, featuring lower distortion, higher slew rate, low output impedance, and high drive current. It effectively meets the listening needs of music lovers.

[0023] In another embodiment of the invention, refer to the appendix. Figure 2 and appendix Figure 3 As shown, this circuit architecture consists of a current-to-voltage conversion circuit and a low-pass filter circuit composed of discrete components.

[0024] Among them, operational amplifiers U1 / U2 are low-voltage noise JFET audio operational amplifiers. The I / V conversion circuit, composed of R5 / R9 (I / V conversion resistors) and external components such as transistors, converts the current output by the DAC chip into an analog voltage signal. C9 and C10 prevent the operational amplifier from self-oscillating at high frequencies. Changing the resistance values ​​of R5 and R9 can change the magnitude of the output voltage.

[0025] In this circuit, setting the value of resistor IV is crucial. Taking the calculation method of the I / V resistance value when connecting the DAC chip ES9038PRO as an example: the ES9038PRO has 8 outputs, so the output current is 15 × 8 = 120mApp. The differential synthesizer amplifier adds the positive and negative values ​​to produce twice the voltage, so only half of the voltage setting is needed for each output voltage. Assuming the current required output voltage is 2Vrms (the normal output of a typical preamp is 2Vrms), then the pp value is 5.6Vpp (amplitude of the effective output 2Vrms), which can be obtained by amplifier IV to get half of it, 2.8Vpp. The value is 2.8Vpp ÷ 0.120 (App) = 23.4Ω. Therefore, in this embodiment, a 24Ω resistor is sufficient.

[0026] In this embodiment, Q1 / Q2 / R1 / R6, Q17 / Q18 / R24 / R25 form a constant current source of approximately 7mA (Vbe / 82R=0.6 / 82=0.0073), which can provide stable operating current to the output stages inside U1 and U2 respectively, improving the linearity of the output stages and reducing distortion.

[0027] In this embodiment, Q6 and Q7, Q19 and Q30 form a cross-type diamond amplifier circuit. Cross-type diamond circuits are characterized by high slew rate, low output impedance, large bandwidth, large output current, and high linearity. Only Q6 and Q7 are needed, and Q19 and Q30 have consistent characteristics, which can reduce the output offset voltage. Therefore, in this embodiment, Q6 and Q7, and Q19 and Q30 all use twin transistors. Combined with the output transistors Q4 and Q10, they can achieve high output linearity and good output capability.

[0028] In this embodiment, Q3 / Q9 / R2 / R3 / R18 / R19 and Q13 / Q16 / R20 / R27 / R21 / R18 form a current mirror constant current source, which are the active load circuits of Q6 / Q7 and Q19 / Q30, respectively. Q3 and Q9 are each composed of two transistors with identical characteristics. Since the base (B) and collector (C) of Q3-B are connected together, the UBE of Q3-B is equal to the UCE, and the collector current of Q3-B is equal to βxIB. The base (BE) terminals of transistors Q3-B and Q3-A are connected, so their base currents IB are equal. Since Q3-A and Q3-B are transistors with identical characteristics, their current amplification factors are the same, and therefore the collector currents of both transistors are equal to IC = βxIB. Therefore, the currents of the two transistors are mirror images. The connection of Q9-A and Q9-B is the same as that of Q3-B and Q3-A, also showing a current mirror relationship. All of these will ensure that the current flowing through voltage amplifier transistors Q6 and Q7 is the same. Changing R2 / R3 and R18 and R19 can change the operating current of this stage, which is set to around 6mA (VBE / 100R).

[0029] Furthermore, the active load circuit using a current mirror constant current source features constant output current, good temperature characteristics, and infinite AC equivalent resistance. In this embodiment, the output transistors Q4 / Q10 and Q11 / Q12 provide quiescent current, enabling them to operate in Class A mode. This avoids crossover distortion in the output transistors, providing the entire unit with a warm, detailed, and pleasant sound quality.

[0030] Q5 and Q8 are overcurrent protection transistors for Q4 and Q10, respectively, while Q15 and Q14 are overcurrent protection transistors for Q11 and Q12, respectively. They limit the input voltage by detecting the current across the emitter resistor, preventing damage to the output transistors due to overcurrent. In this embodiment, R16 / C5 and R31 / C1 form a Jobel network to prevent high-frequency self-oscillation in the power output stage. Op-amp U3-B and R33 / R34 / R35 / R36 / C2 / C3, and U3-A and R37 / R38 / R39 / R40 / C4 / C6 form a low-pass filter with a cutoff frequency of 110kHz, filtering out residual high-frequency noise outside the DAC chip's output band. R41 / C7 and R42 / C8 in the circuit are used to prevent ultra-high frequency interference at the audio output.

[0031] This circuit uses an operational amplifier and discrete components to form an I / V converter, which avoids the above problems and has the advantages of improved output linearity, lower distortion, high slew rate, low output impedance and large drive current.

[0032] This project's circuit is designed for N-channel conversion and differential synthesis output of high-current output audio DACs. The amplifier circuit utilizes a buffer circuit composed of operational amplifiers, reducing the number of components. It is suitable for the receiving end of multi-channel output DACs of current-output Hi-Fi audio DAC chips (such as ES9018S / ES9038PRO / PCM1792 / PCM1794 / AK4499, etc.). This circuit delivers high-performance sound, lower distortion, higher slew rate, low output impedance, and high drive current, meeting the needs of music lovers.

[0033] After multiple experimental verifications, this circuit can achieve the following parameters: frequency response (Ref. 1kHz: 20Hz-20kHz + / - 0.1dB; total harmonic distortion (THD: <0.001%); channel separation @1kHz: >120dB; dynamic range A-weighted: =>110dB.

[0034] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0035] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications, substitutions, and improvements without departing from the concept of the present invention, and these should all be covered within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the claims.

Claims

1. An audio decoding output stage circuit, characterized in that: The device includes an I / V conversion module and a low-pass filter module with electrical connections. The I / V conversion module includes a conversion circuit, a cross-type diamond amplifier circuit, an overcurrent protection circuit, and a Joubert network circuit. The conversion circuit includes a JFET audio operational amplifier chip and an I / V conversion resistor to convert the input current into an analog voltage signal; the input terminal of the cross-type diamond amplifier circuit is connected to the output terminal of the conversion circuit to reduce the input offset voltage; the input terminal of the overcurrent protection circuit is connected to the output terminal of the cross-type diamond amplifier circuit for overcurrent protection; the Jobel network circuit is located at the output terminal of the I / V conversion module to prevent high-frequency self-oscillation of the power output stage. The low-pass filter module includes a filter circuit and an ultra-high frequency filter circuit disposed at the output end of the audio decoding output stage circuit.

2. The audio decoding output stage circuit according to claim 1, characterized in that, The conversion circuit includes a JFET audio operational amplifier chip, a fifth resistor, and a ninth capacitor. The first end of the fifth resistor is connected to the signal input terminal of the JFET audio operational amplifier chip, and the ninth capacitor is connected in parallel across the fifth resistor.

3. The audio decoding output stage circuit according to claim 1, characterized in that, The cross-type diamond amplifier circuit includes a fourth switch, a sixth switch, a seventh switch, and a tenth switch. The sixth and seventh switches are both twins. The controlled terminals of the sixth and seventh switches are connected to the output terminals of the conversion circuit. The output terminals of the sixth and seventh switches are connected to the power supply. The sixth and seventh switches are respectively connected to the controlled terminals of the fourth and tenth switches.

4. The audio decoding output stage circuit according to claim 3, characterized in that, The overcurrent protection circuit includes a fifth switch and an eighth switch; the controlled terminal of the fifth switch is connected to the output terminal of the fourth switch, and the input terminal of the fifth switch is connected to the controlled terminal of the fourth switch. The controlled terminal of the eighth switch is connected to the output terminal of the tenth switch, and the input terminal of the eighth switch is connected to the controlled terminal of the tenth switch.

5. The audio decoding output stage circuit according to claim 2, characterized in that, The conversion circuit also includes a first constant current source circuit, which provides a constant operating current to the output stage of the JFET audio operational amplifier chip.

6. The audio decoding output stage circuit according to claim 5, characterized in that, The first constant current circuit includes a first switching transistor, a second switching transistor, a first resistor, and a sixth resistor. The input terminal of the first switching transistor is connected to a power supply, and the first switching transistor is grounded through the sixth resistor. The first resistor is connected in parallel between the input terminal and the controlled terminal of the first switching transistor. The controlled terminal of the second switching transistor is connected to the output terminal of the first switching transistor, the input of the second switching transistor is connected to the controlled terminal of the first switching transistor, and the output terminal of the second switching transistor is connected to the current terminal of the JFET audio operational amplifier chip.

7. The audio decoding output stage circuit according to claim 3, characterized in that, It also includes a second constant current source circuit, which includes a third switch, a ninth switch, a seventh resistor, a second resistor, a third resistor, an eighteenth resistor, and a nineteenth resistor; the second resistor and the third resistor are respectively disposed between the two input terminals of the third switch and the power supply, and one output terminal of the third switch is connected to the input terminal of the sixth switch; the eighteenth resistor and the nineteenth resistor are respectively disposed between the two input terminals of the ninth switch and the power supply; one output terminal of the ninth switch is connected to the input terminal of the seventh switch, and the other output terminal of the third switch is connected to the other output terminal of the ninth switch through the seventh resistor.

8. The audio decoding output stage circuit according to claim 1, characterized in that, The ultra-high frequency filtering circuit includes a sixteenth resistor and a fifth capacitor connected in parallel. The output terminal of the audio decoding output stage circuit is grounded through the ultra-high frequency filtering circuit.

9. The audio decoding output stage circuit according to claim 1, characterized in that, The Joubert network circuit includes a sixteenth resistor and a fifth capacitor, and the output terminal of the I / V conversion module is grounded through the sixteenth resistor and the fifth capacitor in sequence.

10. An audio device, characterized in that: It includes a decoding chip and an audio decoding output stage circuit as described in any one of claims 1 to 9.

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