High-fidelity I / V conversion circuit for audio DAC

Abstract

The utility model provides a high-fidelity I / V conversion circuit for an audio DAC, which relates to the technical field of conversion circuits, and uses zero devices including operational amplifiers U1 and U2, a resistor R2 and a capacitor C2. The operational amplifier U1, the resistor R2 and the capacitor C2 form a subtractor with low-pass filtering, the positive end and the negative end of the subtractor are connected to the output end L-and the output end L + of the DAC respectively, and the output is L-out; the operational amplifier U2, the resistor R2 and the capacitor C2 form another subtractor with low-pass filtering, the positive end and the negative end of the subtractor are connected to the output end L + and the output end L-of the DAC respectively, and the output is L + out. As the potentials of L + and L-are the same, the direct-current potential of the output end is 0 potential, the alternating-current voltage is doubled, and meanwhile suppression on in-phase alternating-current signals is enhanced. According to the utility model, the suppression of the subtraction circuit to the in-phase alternating current signal is doubled, so that the circuit is lower in bottom noise and lower in distortion degree.

Description

TECHNICAL FIELD

[0001] The utility model relates to the technical field of conversion circuit, especially relates to a high fidelity I / V conversion circuit for audio DAC. BACKGROUND

[0002] Current output type DAC is widely used in high fidelity audio field, and has obvious advantages compared with voltage output type DAC, such as low noise, small distortion and the like, can provide higher quality audio signal output for audio equipment, meet the application scene such as music audiophile and professional audio production that quality of sound is demanding.

[0003] Taking the I / V conversion circuit (shown in the attached drawing 1 of the specification) of ES9038Q2M official as an example, it has many deficiencies. First, the circuit needs to adjust the output DC level to zero potential through RW potentiometer, which is extremely inconvenient in mass production process, increases production process and cost, and the adjustment precision of potentiometer is limited, it is difficult to ensure that the output DC level of each product is accurate to zero, which affects the quality of audio signal. Secondly, when using OPA1612 low noise operational amplifier, the actual measurement by AP515 tester shows that the noise is 3.8uV, and the comprehensive harmonic distortion THD+N (1KHz, 0dB) is -108dB, which is far from the ideal parameters (noise 1.5uV, comprehensive harmonic distortion THD+N (1K, 0dB) -120dB) given by ES9038Q2M official, and the performance advantage of the chip cannot be fully utilized.

[0004] Although the circuit with DC servo (shown in figure 3) is proposed in the official document of ES9039Mpro, which solves the trouble of adjusting potentiometer, but the effect of alternating current part is the same as that of the circuit of the attached drawing 1 of the specification, and the key parameters of audio signal cannot be improved, and a operational amplifier is added to realize the output 0 potential, which leads to the increase of cost, and is not conducive to the improvement of market competitiveness of the product, therefore, we propose a high fidelity I / V conversion circuit for audio DAC. UTILITY MODEL CONTENTS

[0005] The utility model aims at providing a high fidelity I / V conversion circuit for audio DAC to solve the problems proposed in the above background technology.

[0006] In order to achieve the above object, the utility model adopts the following technical scheme: A kind of high fidelity I / V conversion circuit for audio DAC, it is related to conversion circuit technical field, including operational amplifier U1, U2, resistance R2 and capacitor C2;Operational amplifier U1, resistance R2, capacitor C2 constitute a low-pass filter subtraction device, its positive and negative terminals are connected to the output end L- and L+ of DAC respectively, and output is L-out;Operational amplifier U2, resistance R2, capacitor C2 constitute another low-pass filter subtraction device, its positive and negative terminals are connected to the output end L+ and L- of DAC respectively, and output is L+out.Due to the same potential of L+ and L-, make output end direct current potential 0 potential and AC voltage doubling, while enhancing the inhibition to in-phase AC signal.

[0007] As a preferred embodiment, resistance R2 is metal film resistance with accuracy not less than 0.1%, and its power meets the working requirement of circuit, and its resistance value is selected according to output voltage requirement.

[0008] As a preferred embodiment, capacitor C2 is ceramic capacitor with low equivalent series resistance, and its capacitance value is selected according to low-pass filter cutoff frequency requirement.

[0009] As a preferred embodiment, it is suitable for full series ESS and Ti chip, and is used to convert current signal output by current output type DAC into voltage signal, so as to be applied to audio equipment to improve audio quality.

[0010] As a preferred embodiment, operational amplifier adopts OPA1612 low-noise operational amplifier, R2=780Ω, and C2=1nF.

[0011] As a preferred embodiment, its measured bottom noise is 1.8μV by AP515, and comprehensive harmonic distortion THD+N (1KHz, 0dB) is -114dB.

[0012] Compared with prior art, the utility model has the advantages and positive effects that, since direct current voltage of signal input by positive terminal and negative terminal of operational amplifier is same, so direct current potential of operational amplifier output terminal is naturally 0 potential, without additional potentiometer adjustment, circuit structure is simplified, production efficiency and product consistency are improved.Meanwhile, AC voltage with same phase and opposite phase makes output terminal AC voltage doubling, to obtain same output voltage as prior art circuit, R2 is twice as much as R1 in prior art circuit.Moreover, subtraction circuit inhibition to in-phase AC signal is doubled, so that bottom noise is effectively reduced, and distortion degree is improved.AP515 is measured, and the utility model circuit bottom noise is 1.8μV, THD+N (1KHz, 0dB) is -114dB, obviously superior to prior art circuit, can provide purer, higher fidelity audio signal for audio equipment. BRIEF DESCRIPTION OF DRAWINGS

[0013] Fig. 1 for the existing I / V conversion circuit diagram;

[0014] Fig. 2 for the I / V conversion circuit principle diagram of the utility model;

[0015] Fig. 3 for the I / V conversion circuit principle diagram of the utility model. DETAILED DESCRIPTION

[0016] The technical solutions in the embodiments of the utility model will be apparently and completely described below with reference to the drawings in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, rather than all the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the utility model.

[0017] Please refer to Figs. 1-3 The utility model provides a kind of technical scheme: a kind of high fidelity I / V conversion circuit for audio DAC, it is related to conversion circuit technical field, including operational amplifier U1, U2, resistance R2 and capacitor C2;Operational amplifier U1, resistance R2, capacitor C2 constitute a low-pass filter with subtracter, its positive and negative terminal is connected to the output end L- and L+ of DAC respectively, and output is L-out;Operational amplifier U2, resistance R2, capacitor C2 constitute another low-pass filter with subtracter, its positive and negative terminal is connected to the output end L+ and L- of DAC respectively, and output is L+out.Due to the same potential of L+ and L-, make output end direct current potential 0 potential and AC voltage doubling, while enhancing the inhibition to in-phase AC signal.Resistance R2 is metal film resistance with accuracy not less than 0.1%, and its power meets the working requirement of circuit, and its resistance value is selected according to output voltage requirement, capacitor C2 is ceramic capacitor with low equivalent series resistance, and its capacitance is selected according to low-pass filter cut-off frequency requirement, adapts to full system ESS and Ti chip, for converting the current signal of current output type DAC output into voltage signal, to be applied in audio equipment to improve audio quality, and it is 1.8 μV by AP515 actual measurement noise, and comprehensive harmonic distortion THD+N (1KHz, 0dB) is -114dB.

[0018] According to the high requirements of audio processing, an operational amplifier with high gain, low noise, high bandwidth and other characteristics is selected. For example, an audio dedicated operational amplifier chip can be selected, which has a flat frequency response, low distortion and high signal-to-noise ratio in the audio frequency band, can accurately process audio signals, and ensure that the quality of the audio signal is not damaged in the conversion process. The value of R2 is determined according to the relationship with R1 in the existing circuit (R2 is twice R1). When selecting a resistor, its power, accuracy and other factors should be considered. The power should meet the current passing requirement when the circuit is working normally to avoid overheating damage to the resistor; the accuracy should ensure the accurate proportional relationship between R2 and R1 to achieve the expected circuit performance. For example, a metal film resistor with an accuracy of 0.1% can be selected, which has stability and accuracy to meet the circuit requirements. The parameter selection of capacitor C2 should match the requirements such as the cutoff frequency of the low-pass filter. According to the frequency range of the audio signal, calculate the appropriate cutoff frequency and select the appropriate value of the capacitor. At the same time, the withstand voltage value, equivalent series resistance (ESR) and other parameters of the capacitor should be considered. The selection of a capacitor with low ESR can reduce signal loss and distortion. For example, a ceramic capacitor is selected, which has the advantages of low ESR, good high-frequency characteristics and other advantages, which can effectively filter high-frequency noise and improve the quality of the audio signal.

[0019] The above is only a preferred embodiment of the present application, and is not intended to limit the present application in other forms. Any skilled person in the art can modify or change the above disclosed technical content to equivalent embodiments applied to other fields, but any simple modification, equivalent change and modification of the above embodiments without departing from the technical scheme of the present application, according to the technical essence of the present application, still belongs to the protection scope of the present application.

Claims

1. A high fidelity I / V conversion circuit for an audio DAC, characterized by, Including operational amplifier U1, U2, resistor R2 and capacitor C2; operational amplifier U1, resistor R2, capacitor C2 constitute a low-pass filter subtractor, its positive and negative terminals are connected to the output terminal L- and L+ of DAC respectively, and the output is L-out; operational amplifier U2, resistor R2, capacitor C2 constitute another low-pass filter subtractor, its positive and negative terminals are connected to the output terminal L+ and L- of DAC respectively, and the output is L+out, because the potential of L+ and L- is the same, the DC potential of the output terminal is 0 potential and the AC voltage is doubled, at the same time, the suppression of the in-phase AC signal is enhanced.

2. A high fidelity I / V conversion circuit for an audio DAC as claimed in claim 1, characterized in that: Resistor R2 is a metal film resistor with an accuracy of not less than 0.1%, and its power meets the working requirements of the circuit, and its resistance value is selected according to the output voltage requirement.

3. The high-fidelity I / V conversion circuit for an audio DAC of claim 1, wherein: Capacitor C2 is a ceramic capacitor with low equivalent series resistance, and its capacitance value is selected according to the low-pass filter cutoff frequency requirement.

4. The high-fidelity I / V conversion circuit for an audio DAC of claim 1, wherein: Adapted to all ESS and Ti chips, used to convert the current signal output by the current output type DAC into a voltage signal, to be applied in audio equipment to improve audio quality.

5. The high-fidelity I / V conversion circuit for an audio DAC of claim 1, wherein: The operational amplifier uses OPA1612 low-noise operational amplifier, R2=780Ω, C2=1nF, Its AP515 measured bottom noise is 1.8μV, balanced maximum output 4V effective value output, and the total harmonic distortion THD+N is -114dB.

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