Audio circuit

Abstract

Digital or analog audio signals are input to N (N≥1) input pins (P1) to (P2). N In the audio interface circuit (310), analog audio signals are input to N input pins (P1) to (P2). N When ), bias resistors are used to bias the N input pins (P1) to (P2). N Apply bias voltages respectively.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an audio circuit. BACKGROUND

[0002] A transmission method of an audio signal between audio ICs (Integrated Circuits) in which an interface circuit corresponding to the transmission method is mounted is roughly classified into analog transmission and digital transmission.

[0003] Figure 1 (a) and (b) of FIG. 1 are exemplary waveform diagrams of a digital audio signal and an analog audio signal. The digital audio signal is composed of a pulse signal that switches between high (for example, 3.3 V) and low (for example, 0 V) as shown in (a) of FIG. 1. For example, the digital audio signal can be a combination of a plurality of pulse signals (for example, a combination of a clock signal and serial data), or a single pulse signal (for example, a PWM (Pulse Width Modulation) signal, a PDM (Pulse Density Modulation) signal, or a DSD (Direct Stream Digital) signal). The analog audio signal has an analog waveform with a maximum of 2 Vrms as shown in (b) of FIG. 1, for example, in the case of a CD (Compact Disc). Figure 1 Figure 1

[0004] Figure 2 is a diagram showing a conventional audio IC 900. The audio IC 900 is capable of inputting both an analog audio signal and a digital audio signal. The audio IC 900 includes an analog audio interface of 2 pins (Lch, Rch) and a serial input interface of 4 pins (SDTA, LRCLK, BCLK, MCLK).

[0005] The audio IC 900 includes a serial interface circuit (receiver) 902, D / A converters 904, 906, and selectors 908, 910.

[0006] In a case where another IC (Integrated Circuit) or a device having an analog interface is connected to the audio IC 900, the analog audio signal is input to the 2 pins (Lch, Rch) of the analog input, and the 4 pins (SDTA, LRCLK, BCLK, MCLK) of the digital input are not used. The selectors 908, 910 select the analog audio signals of the Lch pin and the Rch pin, and output to an internal circuit not shown.

[0007] ​​When the audio IC900 is connected to other ICs or devices with digital interfaces, the two analog input pins (Lch, Rch) are not used; the digital audio signal is input to the four digital input pins (SDATA, LRCLK, BCLK, MCLK). The serial interface circuit 902 separates the digital audio signal into L and R channels. D / A converters 904 and 906 convert the digital signals of the L and R channels into analog signals. Selectors 908 and 910 select the outputs of D / A converters 904 and 906 and output them to internal circuitry (not shown).

[0008] [Existing Technical Documents]

[0009] [Non-patent literature]

[0010] Patent Document 1: Japanese Patent Application Publication No. 2013-197711

[0011] Patent Document 2: Japanese Patent Application Publication No. 2015-201729 Summary of the Invention

[0012] [The problem the invention aims to solve]

[0013] about Figure 2 The audio IC900 requires a total of 6 input pins for both analog and digital inputs, which increases the chip and package area. Figure 2 The diagram only shows one system input, while the audio IC900 sometimes has four system-level inputs, requiring 6 × 4 = 24 pins.

[0014] This disclosure was made in view of the above-mentioned problems, and one of the exemplary purposes of one of its solutions is to provide an audio circuit with a reduced pin count.

[0015] [Technical solutions used to address technical problems]

[0016] One aspect of this disclosure relates to an audio circuit. The audio circuit includes: N (N≥1) input pins for inputting digital or analog audio signals; an audio interface circuit that applies bias voltages to the N input pins respectively via bias resistors when an analog audio signal is input to the N input pins; and internal circuitry that processes the digital or analog audio signals passing through the audio interface circuit.

[0017] Another aspect of this disclosure relates to an electronic device. The electronic device includes any one of the audio circuits described above.

[0018] Another aspect of this disclosure relates to an in-vehicle audio system. The in-vehicle audio system includes any one of the audio circuits described above.

[0019] In addition, any combination of the above-described elements and a result of converting the expression of the present disclosure between a method, an apparatus, and the like is also effective as the present disclosure. Furthermore, the description of the item (a means for solving the problem) does not describe all the features indispensable to the present disclosure, and thus a sub-combination of the described features can also be the present disclosure.

[0020] Effects of Invention

[0021] According to one aspect of the present disclosure, it is possible to reduce the number of pins of an audio circuit. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 (a) of FIG. 1, Figure 1 (b) of FIG. 1 is an exemplary waveform diagram of a digital audio signal and an analog audio signal.

[0023] Figure 2 is a diagram showing a conventional audio IC.

[0024] Figure 3 is a circuit diagram showing the basic configuration of the audio circuit of the embodiment.

[0025] Figure 4 is an equivalent circuit diagram of the audio circuit when a digital audio signal is input.

[0026] Figure 5 is an equivalent circuit diagram of the audio circuit when an analog audio signal is input.

[0027] Figure 6 is a circuit diagram of the audio circuit of Embodiment 1.

[0028] Figure 7 is a circuit diagram of the audio circuit of Embodiment 2.

[0029] Figure 8 is a circuit diagram of the audio circuit of Embodiment 3.

[0030] Figure 9 is a circuit diagram of the audio circuit of Embodiment 4.

[0031] Figure 10 is a circuit diagram of the audio circuit of Embodiment 5.

[0032] Figure 11 (a) of FIG. 1, Figure 11 (b) of FIG. 1 is a circuit diagram of the audio interface circuit of Modification 2. DETAILED DESCRIPTION

[0033] (Summary of Embodiment)

[0034] The following outlines a summary of several illustrative embodiments of the present disclosure. The summary is provided as a precursor to the detailed description that follows, for the purpose of enabling a basic understanding of the embodiments, simplifying and summarizing several concepts in one or more embodiments, and is not intended to define the breadth of the invention or the scope of the disclosure. Furthermore, the summary is not a general summary of all embodiments that can be considered, and does not limit essential components of the embodiments. For convenience, "one embodiment" is sometimes used to refer to one embodiment (example or modification) or multiple embodiments (examples or modifications) disclosed in the specification.

[0035] The audio circuit of one embodiment includes N (N ≥ 1) input pins that input a digital audio signal or an analog audio signal, an audio interface circuit that applies a bias voltage to each of the N input pins via a bias resistor when an analog audio signal is input to the N input pins, and an internal circuit that processes a digital audio signal or an analog audio signal that passes through the audio interface circuit.

[0036] According to this configuration, both analog input pins and digital input pins can be used, and thus the number of pins can be reduced. Note that the phrase "an analog audio signal (a digital audio signal) is input to the N input pins" does not mean that all the N input pins are used, but means that at least one of them is used.

[0037] In one embodiment, the audio interface circuit can be configured to ground each of the N input pins via a bias resistor when a digital audio signal is input to the N input pins.

[0038] In one embodiment, the audio interface circuit can be configured to ground each of the N input pins via a bias resistor at the start of the audio circuit. In the case where the N input pins are connected to an external circuit that outputs a digital signal, the application of a high voltage to the external circuit at the start of the audio circuit can be prevented.

[0039] In one embodiment, the internal circuit can include a D / A converter that is activated when a digital audio signal is input to the N input pins and converts the digital audio signal into an analog signal, an output selector that selects an output signal of the D / A converter when a digital audio signal is input to the N input pins and selects an analog audio signal when an analog audio signal is input to the N input pins, and an analog processing circuit that processes an output of the output selector.

[0040] Also, in one embodiment, the internal circuit includes an A / D converter which becomes active when an analog audio signal is input to the N input pins and converts the analog audio signal into a digital signal, an output selector which selects the digital audio signal when a digital audio signal is input to the N input pins and selects an output signal of the A / D converter when an analog audio signal is input to the N input pins, and a digital processing circuit which processes an output of the output selector.

[0041] Also, in one embodiment, the bias voltage is 1 / 2 of a power supply voltage of the audio circuit.

[0042] Also, in one embodiment, the audio interface circuit includes a voltage dividing circuit which divides a power supply voltage by 1 / 2, a buffer which accepts an output voltage of the voltage dividing circuit, N bias selectors each of which has a first input terminal connected to an output of the buffer and a second input terminal grounded, and N bias resistors each of which has one end connected to an output terminal of a corresponding bias selector and the other end connected to a corresponding input pin.

[0043] Also, in one embodiment, N = 4, and the digital audio signal is transmitted in a serial form including serial data, an LR clock, a bit clock, and a master clock.

[0044] Also, in one embodiment, N = 3, and the digital audio signal is transmitted in a serial form including serial data, an LR clock, and a bit clock.

[0045] Also, in one embodiment, the digital audio signal is a PWM signal.

[0046] Also, in one embodiment, the analog audio signal is a differential signal.

[0047] Also, in one embodiment, the analog audio signal is a single-ended signal.

[0048] Also, in one embodiment, the audio circuit is integrated in one substrate. The so-called "integrated" includes a case where all the components of the circuit are formed on the substrate and a case where main components of the circuit are integrated, and a part of resistors or capacitors or the like can be provided outside the substrate to adjust the circuit constant. By integrating the circuit on one chip, it is possible to reduce the circuit area and to uniformly maintain the characteristics of the circuit elements.

[0049] (Embodiment)

[0050] Hereinafter, the present disclosure will be described with reference to the accompanying drawings and based on preferred embodiments. The same or equivalent constituent elements, components, and processes shown in the various drawings are labeled with the same reference numerals, and repeated descriptions are omitted where appropriate. Furthermore, the embodiments are not intended to limit the disclosure, but are merely illustrative; all features or combinations thereof described in the embodiments are not necessarily the substantive content of the disclosure.

[0051] In this specification, the term "the state of connection between component A and component B" also includes the case where component A and component B are physically directly connected, or the case where component A and component B are indirectly connected via other components that do not affect the electrical connection state or hinder the function.

[0052] Similarly, the so-called "state in which component C is positioned between component A and component B" includes not only the case where component A and component C, or component B and component C are directly connected, but also the case where they are indirectly connected via other components that do not affect the electrical connection state or hinder the function.

[0053] Figure 3 This is a circuit diagram illustrating the basic configuration of the audio circuit 300 in the embodiment. The audio circuit 300 includes N (N≥1) input pins P1 to P2. N The power supply pin VCC, audio interface circuit 310, and internal circuit 320 are integrated on a semiconductor substrate.

[0054] Digital or analog audio signals are exclusively and selectively input to N input pins P1 to P2. N The audio interface circuit 310 receives inputs to N input pins P1 to P2. N The digital or analog audio signal is supplied to the internal circuit 320 of the subsequent stage.

[0055] The audio interface circuit 310 handles analog audio signals input to N input pins P1 to P2. N At that time, through the bias resistors R11~R1 N To connect N input pins P1 to P N Apply bias voltage V respectively B For example, the bias voltage V B The power supply voltage V to be supplied to the power supply pin VCC CC (e.g., 14.4V) is divided by a resistor voltage divider circuit to obtain a voltage of 1 / 2 (e.g., 7.2V).

[0056] Furthermore, the audio interface circuit 310 is configured such that when a digital audio signal is input to N input pins P1 to PN, it is connected via bias resistors R11 to R1 N To enable N input pins P1 to P N Grounded separately.

[0057] The audio interface circuit 310 includes a voltage dividing circuit 312, a buffer 314, N bias selectors SEL11 to SEL1 N , and N bias resistors R11 to R1 N .

[0058] The voltage dividing circuit 312 includes resistors R21, R22 having equal resistance values, and divides a power supply voltage V CC by 2. The buffer 314 accepts an output voltage of the voltage dividing circuit 312. The buffer 314 is able to be turned off in a case where a digital audio signal is input.

[0059] The first input terminal (1) of the i-th (1≤i≤N) bias selector SEL1 i is connected to an output of the buffer 314, and the second input terminal (2) is grounded.

[0060] One end of the i-th (1≤i≤N) bias resistor R1 i is connected to an output terminal (O) of the corresponding bias selector SEL1 i , and the other end is connected to the corresponding input pin P i .

[0061] The bias selectors SEL11 to SEL1 N are turned on at the first input terminal side when an analog audio signal is input to the N input pins P1 to P N , and are turned on at the second input terminal side when a digital audio signal is input.

[0062] For example, the audio circuit 300 can include a register that stores data specifying a digital input and an analog input, and switch the states of the plurality of bias selectors SEL11 to SEL1 N based on the data. Alternatively, the audio circuit 300 can include a setting pin for specifying a digital input and an analog input, and switch the states of the plurality of bias selectors SEL11 to SEL1 N based on an electrical state of the setting pin.

[0063] The audio interface circuit 310 can be configured such that, at the time of startup of the audio circuit 300, that is, at the time of power-on, the N input pins P1 to P N are grounded via the bias resistors R11 to R1 N , regardless of the state of the register or the setting pin. For example, the audio circuit 300 includes a power-on reset circuit, and in response to an output ground of the power-on reset circuit, the plurality of bias selectors SEL11 to SEL1 NThe initialization is performed so that it becomes on at the side of the second input terminal. Then, when the start of the audio circuit 300 is completed, the states of the plurality of bias selectors SEL11 to SEL1 N are switched based on the states of the registers or the setting pins.

[0064] The above is the basic configuration of the audio circuit 300. Next, the operation thereof is described. Figure 4 is a circuit diagram of the audio circuit 300 when the digital audio signal is input. In M (1≤M≤N) of the plurality of input pins P1 to P N , the digital sound source 402 is connected, and M pulse signals D1 to D M are input from the digital sound source 402. The pulse signals D1 to D M pass through the audio interface circuit 310 and are supplied to the internal circuit 320.

[0065] Figure 5 is a circuit diagram of the audio circuit 300 when the analog audio signal is input. In K (1≤K≤N) of the plurality of input pins P1 to P N , the analog sound source 404 is connected via the coupling capacitors C1 to C K . K analog audio signals A1 to A K output from the analog sound source 404 are shifted by the audio interface circuit 310 so that the center level is the bias voltage V BIAS , and are supplied to the internal circuit 320.

[0066] The above is the operation of the audio circuit 300. According to the audio circuit 300, the analog input pin and the digital input pin can be used in common, and thus the number of pins can be reduced.

[0067] Further, at the start of the audio circuit 300, the audio interface circuit 310 is configured to ground the N input pins via resistors. Thereby, in the case where the digital sound source 402 of the digital output is connected to the input pin, it is possible to prevent the case where a high voltage (V BIAS ) is applied to the output pin of the digital sound source 402 at the start of the audio circuit.

[0068] The present disclosure can be considered as Figure 3 a circuit diagram, or a device, a circuit according to the above description, and is not limited to a specific configuration. Hereinafter, not in order to narrow the scope of the present disclosure, but in order to make the understanding of the substance of the disclosure and the operation of the circuit easy and clear, a more specific configuration example is described.

[0069] (Embodiment 1)

[0070] Figure 6is a circuit diagram of the audio circuit 300A of Embodiment 1. In this embodiment, N = 4. As a digital audio signal, a serial audio signal containing serial data SDATA, LR clock LRCLK, bit clock BCLK, and master clock MCLK can be input into the audio circuit 300A. As such a digital audio signal, I 2 PCM audio data of S format, the digital audio signal contains audio signals of 2 channels (for the sake of convenience, called L channel and R channel). Further, in the case of a multi-channel audio signal of 4 channels or more, a TDM (Time Division Multiplex) format can also be used.

[0071] Further, analog audio signals of 2 channels (L channel and R channel) can be input into the audio circuit 300A in a differential form (balanced).

[0072] In the case where a digital sound source is connected, the serial data SDATA, the LR clock LRCLK, the bit clock BCLK, and the master clock MCLK are input into the 1st input pin P1 to the 4th input pin P4. They correspond to Figure 1 the pulse signals of the serial data SDATA, the LR clock LRCLK, the bit clock BCLK, and the master clock MCLK.

[0073] In the case where an analog sound source is connected, a differential analog audio signal AL P , AL N of 1 channel amount (for example, L channel) can be input into the 1st input pin P1 and the 2nd input pin P2. A differential analog audio signal AR P , AR N of another 1 channel amount (for example, R channel) can be input into the 3rd input pin P3 and the 4th input pin P4.

[0074] The internal circuit 320A contains Schmitt buffers B11 to B14, a serial audio interface circuit 322A, D / A converters 324L, 324R, output selectors SEL21 to SEL24, output buffers B21 to B24, and an analog processing circuit 330.

[0075] The serial audio interface circuit 322A, the D / A converters 324L, 324R become active when a digital audio signal is input into the input pins P1 to P4, and separate the received serial data into digital signals of L channel and R channel. The D / A converter 324L converts the digital signal of L channel into an analog signal, and the D / A converter 324R converts the digital signal of R channel into an analog signal. In Embodiment 1, the D / A converters 324L, 324R have differential outputs. Alternatively, the D / A converters 324L, 324R can collectively constitute a digital section.

[0076] The output selectors SEL21 to SEL24 select the output signals of the D / A converters 324L, 324R when digital audio signals are input to the input pins P1 to P4, and select analog audio signals when analog audio signals are input to the input pins P1 to P4.

[0077] Specifically, the first input terminal (1) of the output selector SEL21 is connected to the input pin P1, and the second input terminal (2) is connected to the positive output of the D / A converter 324L. The first input terminal (1) of the output selector SEL22 is connected to the input pin P2, and the second input terminal (2) is connected to the negative output of the D / A converter 324L. The first input terminal (1) of the output selector SEL23 is connected to the input pin P3, and the second input terminal (2) is connected to the positive output of the D / A converter 324R. The first input terminal (1) of the output selector SEL24 is connected to the input pin P4, and the second input terminal (2) is connected to the negative output of the D / A converter 324R.

[0078] The output buffers B21 to B24 receive the outputs of the output selectors SEL21 to SEL24 and supply them to the analog processing circuit 330 in the subsequent stage. Alternatively, the output buffers B21 to B24 can be omitted.

[0079] According to the audio circuit 300A, it is possible to receive digital audio signals in serial form or differential analog audio signals via the four input pins P1 to P4. The number of input pins of the audio circuit 300A is reduced by two as compared with the audio circuit 900 of Figure 2

[0080] In addition, as a modification of the audio circuit 300A, Figure 6 It is also effective to change the D / A converters 324L, 324R to single-ended outputs or to input single-ended analog audio signals to two of the input pins P1 to P4.

[0081] (Embodiment 2)

[0082] Figure 7 is a circuit diagram of the audio circuit 300B of Embodiment 2. In this embodiment, N = 3. As digital audio signals, it is possible to input serial audio signals including serial data SDATA, LR clock LRCLK, and bit clock BCLK to the audio circuit 300B. As such digital audio signals, I2S format PCM audio data is exemplified, and the digital audio signals include audio signals of two channels (for the sake of convenience, referred to as L channel and R channel). Furthermore, in the case of multi-channel audio signals of four channels or the like, a TDM (Time Division Multiplexing) format can be used. 2 S format PCM audio data, the digital audio signals include audio signals of two channels (for the sake of convenience, referred to as L channel and R channel). Furthermore, in the case of multi-channel audio signals of four channels or the like, a TDM (Time Division Multiplexing) format can be used. ​

[0083] Further, the analog audio signals AL, AR of 2 channels (L channel and R channel) can be input to the audio circuit 300B in single-ended (non-balanced-balanced).

[0084] In the case where a digital sound source is connected, the serial data SDATA, the LR clock LRCLK, the bit clock BCLK, and the master clock MCLK are input to the 1st to 3rd input pins P1 to P3. They correspond to Figure 1 the pulse signals of the

[0085] In the case where an analog sound source is connected, the analog audio signal AL of 1 channel amount (for example, L channel) can be input to the 1st input pin P1. The analog audio signal AR of another 1 channel amount (for example, R channel) can be input to the 2nd input pin P2.

[0086] The internal circuit 320B includes the Schmitt buffers B11 to B13, the serial audio interface circuit 322B, the D / A converters 324L, 324R, the output selectors SEL21 to SEL22, the output buffers B21 to B22, and the analog processing circuit 330.

[0087] The serial audio interface circuit 322B, the D / A converters 324L, 324R are activated when the digital audio signals are input to the input pins P1 to P3, and separate the received serial data into the digital signals of L channel and R channel. The D / A converter 324L converts the digital signal of L channel into an analog signal, and the D / A converter 324R converts the digital signal of R channel into an analog signal. In Embodiment 2, the D / A converters 324L, 324R have single-ended outputs.

[0088] The output selectors SEL21 to SEL22 select the output signals of the D / A converters 324L, 324R when the digital audio signals are input to the input pins P1 to P3, and select the analog audio signals when the analog audio signals are input to the input pins P1, P2.

[0089] Specifically, the 1st input terminal (1) of the output selector SEL21 is connected to the input pin P1, and the 2nd input terminal (2) is connected to the output of the D / A converter 324L. The 1st input terminal (1) of the output selector SEL21 is connected to the input pin P2, and the 2nd input terminal (2) is connected to the output of the D / A converter 324R.

[0090] The output buffers B21 to B22 accept the outputs of the output selectors SEL21 to SEL22, and supply them to the analog processing circuit 330 of the subsequent stage. Alternatively, the output buffers B21 to B22 can be omitted.

[0091] According to the audio circuit 300B, a digital audio signal in serial form or an analog audio signal in single-ended form can be received via 3 input pins P1-P3. The number of input pins of the audio circuit 300A is reduced by 3 compared with the audio circuit 900 of Figure 2

[0092] (Embodiment 3)

[0093] Figure 8 is a circuit diagram of the audio circuit 300C of Embodiment 3. In this embodiment, N=2. As a digital audio signal, a signal in S / PDIF (Sony Philips Digital InterFace) form can be input to the audio circuit 300C.

[0094] Further, analog audio signals AL, AR of 2 channels (L channel and R channel) can be input to the audio circuit 300C in single-ended (unbalanced-balanced) form.

[0095] In the case where a digital sound source is connected, an S / PDIF signal is input to the 1st input pin P1.

[0096] In the case where an analog sound source is connected, an analog audio signal AL of 1 channel amount (e.g., L channel) can be input to the 1st input pin P1 in single-ended form. An analog audio signal AR of another 1 channel amount (e.g., R channel) can be input to the 2nd input pin P2 in single-ended form.

[0097] The internal circuit 320C includes Schmitt buffers B11-B12, an S / PDIF circuit 322C, D / A converters 324L, 324R, output selectors SEL21-SEL22, output buffers B21-B22, and an analog processing circuit 330.

[0098] The S / PDIF circuit 322C, D / A converters 324L, 324R are activated when an S / PDIF signal is input to the input pin P1, and separate the received S / PDIF signal into digital signals of L channel and R channel. The D / A converter 324L converts the digital signal of L channel into an analog signal, and the D / A converter 324R converts the digital signal of R channel into an analog signal. The other configurations are the same as those of the internal circuit 320B of Figure 7 (Embodiment 2).

[0099] According to the audio circuit 300C, a digital audio signal in serial form or an analog audio signal in single-ended form can be received via 2 input pins P1, P2.

[0100] (Embodiment 4) ​

[0101] Figure 9 is a circuit diagram of the audio circuit 300D of Embodiment 4. In this embodiment, N = 2. As a digital audio signal, a pulse-modulated signal DL, DR such as a PDM signal (DSD signal) or a PWM signal can be directly input to the audio circuit 300D.

[0102] Further, analog audio signals AL, AR of 2 channels (L channel and R channel) can be input to the audio circuit 300D in single-ended (non-balanced-balanced).

[0103] In a case where a digital sound source is connected, pulse-modulated signals DL, DR of L channel and R channel can be respectively input to input pins P1, P2.

[0104] In a case where an analog sound source is connected, a single-ended analog audio signal AL of 1 channel amount (e.g., L channel) can be input to the 1st input pin P1. A single-ended analog audio signal AR of another 1 channel amount (e.g., R channel) can be input to the 2nd input pin P2.

[0105] The internal circuit 320D includes Schmitt buffers B11 to B12, a decoder circuit 322D, D / A converters 324L, 324R, output selectors SEL21 to SEL22, output buffers B21 to B22, and an analog processing circuit 330.

[0106] The decoder circuit 322D is activated when the pulse-modulated signals DL, DR are input to the input pins P1, P2, and decodes the received pulse-modulated signals DL, DR. The D / A converters 324L, 324R convert digital signals of L channel and R channel into analog signals. It is also possible to replace the decoder circuit 322D and the D / A converters 324L, 324R with analog low-pass filters. The other configurations are the same as those of the internal circuit 320B of Embodiment 2. Figure 7

[0107] According to the audio circuit 300D, a pulse-modulated digital audio signal or a single-ended analog audio signal can be received via 2 input pins P1, P2.

[0108] (Embodiment 5)

[0109] In Embodiments 1 to 4, the audio circuit including the analog processing circuit 330 is described, but the present disclosure can also be applied to an audio circuit including a digital processing circuit 340. Figure 10 is a circuit diagram of the audio circuit 300E of Embodiment 5. The audio circuit 300E can receive a pulse-modulated digital audio signal or a single-ended analog audio signal via 2 input pins P1, P2. Figure 6 ​the same signal as the audio circuit 300A, but does not include the analog processing circuit 330, the D / A converter 324, and instead includes the digital processing circuit 340 and the A / D converter 326.

[0110] The A / D converter 326L and the A / D converter 326R become active when an analog audio signal is input to the input pins P1 to P4, and convert the analog audio signal into a digital signal. Specifically, the A / D converter 326L has a differential input, and converts the differential analog signal AL P , AL N of the L channel input to the input pins P1, P2 into a digital signal. Further, the A / D converter 326R has a differential input, and converts the differential analog signal AR P , AR N of the R channel input to the input pins P3, P4 into a digital signal.

[0111] The digital processing circuit 340 processes the output of the A / D converter 326L, 326R when an analog signal is input to the input pins P1 to P4, and processes the output of the serial audio interface circuit 322E when a digital audio signal is input to the input pins P1 to P4.

[0112] For example, the digital processing circuit 340 can include output selectors SEL31, SEL32 that select a digital audio signal when a digital audio signal is input to the input pins P1 to P4, and select the output signal of the A / D converter 326 when an analog audio signal is input.

[0113] (Modified Example 1)

[0114] For Embodiments 2 to 4, as well as for Embodiment 5, the analog processing circuit 330 can be replaced with the digital processing circuit 340.

[0115] (Modified Example 2)

[0116] The configuration of the audio interface circuit 310 is not limited to Figure 3 the configuration. Figure 11 (a) of Figure 11 (b) is a circuit diagram of the audio interface circuit 310 of Modified Example 2. In Figure 11 (a) of Figure 11 (b), only the portion corresponding to one pin is shown. In Figure 11 the modified example of (a), 2 bias resistors R1 # are provided on the input side of the bias selector SEL1 # In Figure 11 (b), instead of the bias selector SEL1 #The switch SW1 is provided on the input side of the bias resistor R1 # When an analog audio signal is input, the switch SW1 is turned on # The bias voltage V BIAS is applied to the input pin P# via the bias resistor R1 # and the switch SW1 # . Alternatively, the bias resistor R1 # and the switch SW1 # may be exchanged.

[0117] [Industrial applicability]

[0118] The present disclosure relates to an audio circuit.

[0119] [Explanation of reference numerals]

[0120] 300 audio circuit

[0121] 310 audio interface circuit

[0122] 312 voltage dividing circuit

[0123] 314 buffer

[0124] 320 internal circuit

[0125] 322A, 322B serial audio interface circuit

[0126] 322CS / PDIF circuit

[0127] 322D decoder circuit

[0128] 324 D / A converter

[0129] 326 A / D converter

[0130] 330 analog processing circuit

[0131] 340 digital processing circuit

[0132] 404 analog sound source

[0133] 402 digital sound source

Claims

1. An audio circuit, characterized by comprising: N input pins for inputting a digital audio signal or an analog audio signal, where N ≥ 1, an audio interface circuit which applies a bias voltage to each of the N input pins via a bias resistor when the analog audio signal is input to the N input pins, and an internal circuit which processes the digital audio signal or the analog audio signal passed through the audio interface circuit, the bias voltage is 1 / 2 of a power supply voltage of the audio circuit, the audio interface circuit includes: a voltage dividing circuit which divides the power supply voltage by 1 / 2, a buffer which accepts an output voltage of the voltage dividing circuit, N bias selectors each having a first input terminal connected to an output of the buffer and a second input terminal grounded, and N bias resistors each having one end connected to an output terminal of a corresponding bias selector and the other end connected to a corresponding input pin.

2. The audio circuit according to claim 1, wherein the audio interface circuit is configured to ground each of the N input pins via the bias resistor when the digital audio signal is input to the N input pins.

3. The audio circuit according to claim 2, wherein at the start of the audio circuit, the audio interface circuit is configured to ground each of the N input pins via the bias resistor.

4. The audio circuit according to any one of claims 1 to 3, wherein the internal circuit includes: a D / A converter which is activated when the digital audio signal is input to the N input pins and converts the digital audio signal into an analog signal, an output selector which selects an output signal of the D / A converter when the digital audio signal is input to the N input pins and selects the analog audio signal when the analog audio signal is input to the N input pins, and an analog processing circuit which processes an output of the output selector.

5. The audio circuit according to any one of claims 1 to 3, wherein the internal circuit includes: an A / D converter which is activated when the analog audio signal is input to the N input pins and converts the analog audio signal into a digital signal, an output selector which selects the digital audio signal when the digital audio signal is input to the N input pins and selects an output signal of the A / D converter when the analog audio signal is input to the N input pins, and a digital processing circuit which processes an output of the output selector.

6. The audio circuit according to any one of claims 1 to 3, wherein N = 4, and the digital audio signal is transmitted in a serial form including serial data, an LR clock, a bit clock, and a master clock.

7. The audio circuit according to any one of claims 1 to 3, wherein N = 3, and the digital audio signal is transmitted in a serial form including serial data, an LR clock, and a bit clock.

8. The audio circuit according to any one of claims 1 to 3, wherein the digital audio signal is a PWM signal.

9. The audio circuit according to any one of claims 1 to 3, wherein the analog audio signal is a differential signal.

10. The audio circuit according to any one of claims 1 to 3, wherein the analog audio signal is a single-ended signal.

11. The audio circuit according to any one of claims 1 to 3, wherein the audio circuit is integrated in a single substrate.

Images