Audio circuit

Abstract

In the present invention, a digital audio signal or an analog audio signal is input to N (N≧1) input pins P1-PN. When an analog audio signal is input to N input pins P1-PN, an audio interface circuit 310 imparts a bias voltage, via a bias resistance, to each of the N input pins P1-PN.

Description

[Technical Field]

[0001] The present disclosure relates to audio circuits. [Background technology]

[0002] The methods of transmitting audio signals between audio integrated circuits (ICs) are broadly classified into analog transmission and digital transmission, and audio ICs are equipped with interface circuits that correspond to the transmission method.

[0003] 1(a) and 1(b) are exemplary waveform diagrams of a digital audio signal and an analog audio signal. As shown in FIG. 1(a), the digital audio signal is composed of a pulse signal that switches between two levels: high (e.g., 3.3 V) and low (e.g., 0 V). For example, the digital audio signal may be a combination of multiple pulse signals (e.g., a combination of a clock signal and serial data), or a single pulse signal (e.g., a PWM (Pulse Width Modulation) signal, a PDM (Pulse Density Modulation) signal, or a DSD (Direct Stream Digital) signal). As shown in FIG. 1(b), the analog audio signal has an analog waveform of up to 2 Vrms in the case of a CD (Compact Disc), for example.

[0004] Figure 2 shows a conventional audio IC 900. This audio IC 900 can input both analog and digital audio signals. The audio IC 900 has a two-pin (Lch, Rch) analog audio interface and a four-pin (SDATA, LRCLK, BCLK, MCLK) serial input interface.

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

[0006] When another IC (Integrated Circuit) or device with an analog interface is connected to the audio IC 900, an analog audio signal is input to the two analog input pins (Lch, Rch), and the four digital input pins (SDATA, LRCLK, BCLK, MCLK) are unused. Selectors 908 and 910 select the analog audio signal from the Lch pin or the Rch pin and output it to an internal circuit (not shown).

[0007] When another IC or device with a digital interface is connected to the audio IC 900, the two analog input pins (Lch, Rch) are unused, and a digital audio signal is input to the four digital input pins (SDATA, LRCLK, BCLK, MCLK). A serial interface circuit 902 separates the digital audio signal into an L channel and an R channel. D / A converters 904, 906 convert the L channel and R channel digital signals into analog signals. Selectors 908, 910 select the outputs of the D / A converters 904, 906 and output them to internal circuits (not shown). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-197711 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-201729 Summary of the Invention [Problem to be solved by the invention]

[0009] The audio IC 900 in Figure 2 requires a total of six input pins for analog and digital inputs, which poses the problem of increasing the chip and package area. Although Figure 2 shows only one input system, the audio IC 900 may have up to four input systems, requiring 6 x 4 = 24 pins.

[0010] The present disclosure has been made in view of the above-mentioned problems, and one exemplary purpose of an embodiment thereof is to provide an audio circuit with a reduced number of pins. [Means for solving the problem]

[0011] An aspect of the present disclosure relates to an audio circuit including: N (N≧1) input pins to which digital audio signals or analog audio signals are input; an audio interface circuit that applies a bias voltage to each of the N input pins via a bias resistor when the analog audio signals are input to the N input pins; and an internal circuit that processes the digital audio signals or analog audio signals that have passed through the audio interface circuit.

[0012] Another aspect of the present disclosure relates to an electronic device including any of the audio circuits described above.

[0013] Another aspect of the present disclosure relates to an in-vehicle audio system including any one of the audio circuits described above.

[0014] Any combination of the above components, and conversion of the expressions of the present disclosure into methods, devices, etc. are also valid aspects of the present disclosure. Furthermore, the description in this section (Means for Solving the Problems) does not describe all essential features of the present disclosure, and therefore, subcombinations of the described features may also be included in the present disclosure. [Effects of the Invention]

[0015] According to certain aspects of the present disclosure, the number of pins in an audio circuit can be reduced. [Brief explanation of the drawings]

[0016] [Figure 1] 1(a) and 1(b) are exemplary waveform diagrams of a digital audio signal and an analog audio signal. [Figure 2]FIG. 1 is a diagram illustrating a conventional audio IC. [Figure 3] 1 is a circuit diagram showing a basic configuration of an audio circuit according to an embodiment; [Figure 4] 2 is an equivalent circuit diagram of an audio circuit when a digital audio signal is input. FIG. [Figure 5] 2 is an equivalent circuit diagram of an audio circuit when an analog audio signal is input. FIG. [Figure 6] 1 is a circuit diagram of an audio circuit according to a first embodiment. [Figure 7] FIG. 10 is a circuit diagram of an audio circuit according to a second embodiment. [Figure 8] FIG. 10 is a circuit diagram of an audio circuit according to a third embodiment. [Figure 9] FIG. 10 is a circuit diagram of an audio circuit according to a fourth embodiment. [Figure 10] FIG. 10 is a circuit diagram of an audio circuit according to a fifth embodiment. [Figure 11] 11(a) and 11(b) are circuit diagrams of an audio interface circuit according to the second modification. DETAILED DESCRIPTION OF THE INVENTION

[0017] (Outline of the embodiment) A summary of some exemplary embodiments of the present disclosure is provided. This summary is intended to provide a simplified overview of some concepts of one or more embodiments in order to provide a basic understanding of the embodiments as a prelude to the more detailed description that follows. It is not intended to limit the scope of the invention or disclosure. Furthermore, this summary is not an exhaustive overview of all possible embodiments, nor does it limit essential elements of the embodiments. For convenience, the term "one embodiment" may refer to one embodiment (example or variant) or multiple embodiments (examples or variants) disclosed herein.

[0018] An audio circuit according to one embodiment includes N (N≧1) input pins to which digital audio signals or analog audio signals are input, 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 the digital audio signal or analog audio signal that has passed through the audio interface circuit.

[0019] This configuration allows analog input pins and digital input pins to be used interchangeably, reducing the number of pins. Note that "analog audio signals (digital audio signals) are input to N input pins" does not mean that all N input pins are used, but rather that at least one of them is used.

[0020] In one embodiment, the audio interface circuit may ground each of the N input pins via a bias resistor when digital audio signals are input to the N input pins.

[0021] In one embodiment, the audio interface circuit may be configured to ground each of the N input pins via a bias resistor when the audio circuit is started up. In a case where an external digital output circuit is connected to the N input pins, it is possible to prevent a high voltage from being applied to the external circuit when the audio circuit is started up.

[0022] In one embodiment, the internal circuit may include a D / A converter that becomes active when digital audio signals are input to the N input pins and converts the digital audio signals into analog signals, an output selector that selects an output signal of the D / A converter when digital audio signals are input to the N input pins and selects an analog audio signal when analog audio signals are input to the N input pins, and an analog processing circuit that processes the output of the output selector.

[0023] In one embodiment, the internal circuit may include an A / D converter that becomes active when analog audio signals are input to the N input pins and converts the analog audio signals into digital signals, an output selector that selects the digital audio signals when digital audio signals are input to the N input pins and selects the output signal of the A / D converter when analog audio signals are input to the N input pins, and a digital processing circuit that processes the output of the output selector.

[0024] In one embodiment, the bias voltage may be half the power supply voltage of the audio circuit.

[0025] In one embodiment, the audio interface circuit may include a voltage divider circuit that divides the power supply voltage by 2; a buffer that receives the output voltage of the voltage divider circuit; N bias selectors, each having a first input terminal connected to the output of the buffer and a second input terminal grounded; and N bias resistors, each having one end connected to the output terminal of a corresponding bias selector and the other end connected to a corresponding input pin.

[0026] In one embodiment, N=4, and the digital audio signal may be transmitted in a serial format including serial data, LR clock, bit clock, and master clock.

[0027] In one embodiment, N=3, and the digital audio signal may be transmitted in a serial format including serial data, an LR clock, and a bit clock.

[0028] In one embodiment, the digital audio signal may be a PWM signal.

[0029] In one embodiment, the analog audio signal may be a differential signal.

[0030] In one embodiment, the analog audio signal may be a single-ended signal.

[0031] In one embodiment, the audio circuit may be monolithically integrated on a single substrate. "Monolithically integrated" includes cases where all of the circuit components are formed on the substrate, or where the main circuit components are monolithically integrated, and some resistors, capacitors, etc. may be provided outside the substrate to adjust the circuit constants. By integrating the circuit on a single chip, the circuit area can be reduced and the characteristics of the circuit elements can be maintained uniformly.

[0032] (Embodiment) The present disclosure will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, parts, and processes shown in each drawing are designated by the same reference numerals, and redundant descriptions will be omitted where appropriate. Furthermore, the embodiments are illustrative and do not limit the disclosure, and all features and combinations thereof described in the embodiments are not necessarily essential to the disclosure.

[0033] In this specification, "a state in which component A is connected to component B" includes cases in which component A and component B are directly physically connected, and cases in which component A and component B are indirectly connected via other components that do not affect the electrical connection state or inhibit function. Similarly, "a state in which component C is provided between component A and component B" includes not only cases in which components A and C, or components B and C, are directly connected, but also cases in which they are indirectly connected via other components that do not affect the electrical connection state or impede function.

[0034] 3 is a circuit diagram showing the basic configuration of an audio circuit 300 according to an embodiment. The audio circuit 300 has N (N≧1) input pins P1 to P N , a power supply pin VCC, an audio interface circuit 310, and an internal circuit 320, which are integrated on a single semiconductor substrate.

[0035] N input pins P1 to P N The audio interface circuit 310 has N input pins P1 to P2, to which digital audio signals or analog audio signals are input either exclusively or alternatively. N and supplies the digital or analog audio signal input to the internal circuit 320 at the subsequent stage.

[0036] The audio interface circuit 310 has N input pins P1 to P N When an analog audio signal is input to the N Each bias resistor R11 to R1 N via the bias voltage V B For example, a bias voltage V B is the power supply voltage V supplied to the power supply pin VCC CC (for example, 14.4V) is divided in half by a resistor voltage divider circuit to produce a voltage (for example, 7.2V).

[0037] The audio interface circuit 310 also has N input pins P1 to P N When a digital audio signal is input to the N Each bias resistor R11 to R1 N The power supply is configured to be grounded via

[0038] The audio interface circuit 310 includes a voltage divider circuit 312, a buffer 314, and N bias selectors SEL11 to SEL1 N , N bias resistors R11 to R1 N Equipped with.

[0039] The voltage divider circuit 312 includes resistors R21 and R22 having equal resistance values, and divides the power supply voltage V CC The buffer 314 receives the output voltage of the voltage dividing circuit 312. The buffer 314 can be turned off when a digital audio signal is input.

[0040] i-th (1≦i≦N) bias selector SEL1 i The first input terminal (1) of the input terminal (2) is connected to the output of the buffer 314, and the second input terminal (2) is grounded.

[0041] i-th (1≦i≦N) bias resistor R1 i One end of the corresponding bias selector SEL1 i The other end is connected to the corresponding input pin P i and is connected.

[0042] Bias selectors SEL11 to SEL1 N is N input pins P1 to P N When an analog audio signal is input to the first input terminal, the first input terminal is turned on, and when a digital audio signal is input to the second input terminal, the second input terminal is turned on.

[0043] For example, the audio circuit 300 includes a register for storing data specifying digital input and analog input, and multiple bias selectors SEL11 to SEL1 N Alternatively, the audio circuit 300 may be provided with setting pins for specifying digital input and analog input, and may select a plurality of bias selectors SEL11 to SEL1 N The state of may be switched based on the electrical state of a configuration pin.

[0044] When the audio circuit 300 is started up, that is, when the power is turned on, the audio interface circuit 310 outputs the N input pins P1 to P2 regardless of the state of the registers and setting pins. N Each of them is bias resistor R11 to R1 N For example, the audio circuit 300 may be configured to include a power-on reset circuit, and to select a plurality of bias selectors SEL11 to SEL1 in response to the output of the power-on reset circuit. NAfter that, when the start-up of the audio circuit 300 is completed, the bias selectors SEL11 to SEL1 N You may switch the state of

[0045] The above is the basic configuration of the audio circuit 300. Next, its operation will be described. Fig. 4 is an equivalent circuit diagram of the audio circuit 300 when a digital audio signal is input. A plurality of input pins P1 to P N A digital sound source 402 is connected to M (1≦M≦N) of the M Pulse signals D1 to D M passes through the audio interface circuit 310 and is supplied to the internal circuit 320.

[0046] 5 is an equivalent circuit diagram of the audio circuit 300 when an analog audio signal is input. N Among them, K (1≦K≦N) coupling capacitors C1 to C K The analog sound source 404 is connected to the cascade connection 401 via the analog audio signal generator 404. The analog sound source 404 outputs K analog audio signals A1 to A K The audio interface circuit 310 adjusts the center level to the bias voltage V BIAS and is supplied to the internal circuit 320.

[0047] This completes the operation of the audio circuit 300. According to this audio circuit 300, the analog input pins and digital input pins can be used interchangeably, thereby reducing the number of pins.

[0048] Furthermore, when the audio circuit 300 is started up, the audio interface circuit 310 is configured so that each of the N input pins is grounded via a resistor. As a result, when a digital sound source 402 with digital output is connected to the input pins, a high voltage (V BIAS) can be prevented from being applied.

[0049] The present disclosure encompasses various devices and circuits that can be understood as the circuit diagram in Figure 3 or derived from the above description, and is not limited to any particular configuration. Below, more specific configuration examples will be described not to narrow the scope of the present disclosure, but to facilitate and clarify understanding of the essence of the disclosure and circuit operation.

[0050] Example 1 FIG. 6 is a circuit diagram of an audio circuit 300A according to a first embodiment. In this embodiment, N=4. A serial audio signal including serial data SDATA, an LR clock LRCLK, a bit clock BCLK, and a master clock MCLK can be input to the audio circuit 300A as a digital audio signal. Such a digital audio signal can be 2 The example shows PCM audio data in S format, and the digital audio signal includes a two-channel (conveniently referred to as L channel and R channel) audio signal. For multi-channel audio signals such as four channels, a TDM (time division modulation) format may be used.

[0051] Furthermore, analog audio signals of two channels (L channel and R channel) can be input to the audio circuit 300A in a differential format (balanced).

[0052] When a digital sound source is connected, serial data SDATA, LR clock LRCLK, bit clock BCLK, and master clock MCLK are input to the first input pin P1 to the fourth input pin P4, which correspond to the pulse signals in FIG.

[0053] When an analog sound source is connected, the first input pin P1 and the second input pin P2 receive a differential analog audio signal AL for one channel (for example, the L channel). P ,AL NA differential analog audio signal AR for another channel (for example, the R channel) can be input to the third input pin P3 and the fourth input pin P4. P ,AR N can be entered.

[0054] The internal circuit 320A includes Schmitt buffers B11 to B14, a serial audio interface circuit 322A, D / A converters 324L and 324R, output selectors SEL21 to SEL24, output buffers B21 to B24, and an analog processing circuit 330.

[0055] The serial audio interface circuit 322A and the D / A converters 324L, 324R become active when digital audio signals are input to the input pins P1 to P4, and separate the received serial data into L-channel and R-channel digital signals. The D / A converter 324L converts the L-channel digital signal into an analog signal, and the D / A converter 324R converts the R-channel digital signal into an analog signal. In the first embodiment, the D / A converters 324L, 324R have differential outputs. Note that the D / A converters 324L, 324R may be configured with a common digital section.

[0056] The output selectors SEL21 to SEL24 select the output signals of the D / A converters 324L and 324R when digital audio signals are input to the input pins P1 to P4, and select the analog audio signals when analog audio signals are input to the input pins P1 to P4.

[0057] 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 SEL21 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.

[0058] The output buffers B21 to B24 receive the outputs of the output selectors SEL21 to SEL24 and supply them to the subsequent analog processing circuit 330. The output buffers B21 to B24 may be omitted.

[0059] This audio circuit 300A can receive serial digital audio signals or differential analog audio signals via four input pins P1 to P4. The number of input pins of the audio circuit 300A is two less than that of the audio circuit 900 in FIG.

[0060] As a modified example of the audio circuit 300A of FIG. 6, it is also effective to change the D / A converters 324L and 324R to single-ended outputs, or to input single-ended analog audio signals to two of the input pins P1 to P4.

[0061] Example 2 FIG. 7 is a circuit diagram of an audio circuit 300B according to a second embodiment. In this embodiment, N=3. A serial audio signal including serial data SDATA, an LR clock LRCLK, and a bit clock BCLK can be input to the audio circuit 300B as a digital audio signal. Such a digital audio signal can be 2The example shows PCM audio data in S format, and the digital audio signal includes a two-channel (conveniently referred to as L channel and R channel) audio signal. For multi-channel audio signals such as four channels, a TDM (time division modulation) format may be used.

[0062] Furthermore, two-channel (L channel and R channel) analog audio signals AL and AR can be input to the audio circuit 300B in a single-ended (unbalanced) manner.

[0063] When a digital sound source is connected, serial data SDATA, LR clock LRCLK, bit clock BCLK, and master clock MCLK are input to the first input pin P1 to the third input pin P3, which correspond to the pulse signals in FIG.

[0064] When an analog sound source is connected, a single-ended analog audio signal AL of one channel (e.g., L channel) can be input to the first input pin P1, and a single-ended analog audio signal AR of another channel (e.g., R channel) can be input to the second input pin P2.

[0065] The internal circuit 320B includes Schmitt buffers B11 to B13, a serial audio interface circuit 322B, D / A converters 324L and 324R, output selectors SEL21 to SEL22, output buffers B21 and B22, and an analog processing circuit 330.

[0066] The serial audio interface circuit 322B and the D / A converters 324L, 324R become active when digital audio signals are input to the input pins P1 to P3, and separate the received serial data into L-channel and R-channel digital signals. The D / A converter 324L converts the L-channel digital signal into an analog signal, and the D / A converter 324R converts the R-channel digital signal into an analog signal. In the second embodiment, the D / A converters 324L, 324R have single-ended outputs.

[0067] The output selectors SEL21 and SEL22 select the output signals of the D / A converters 324L and 324R when digital audio signals are input to the input pins P1 to P3, and select the analog audio signals when analog audio signals are input to the input pins P1 and P2.

[0068] 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 output of the D / A converter 324L. The first input terminal (1) of the output selector SEL21 is connected to the input pin P2, and the second input terminal (2) is connected to the output of the D / A converter 324R.

[0069] The output buffers B21 and B22 receive the outputs of the output selectors SEL21 and SEL22 and supply them to the subsequent analog processing circuit 330. The output buffers B21 and B22 may be omitted.

[0070] This audio circuit 300B can receive serial digital audio signals or single-ended analog audio signals via three input pins P1 to P3. The number of input pins of the audio circuit 300A is three less than that of the audio circuit 900 in FIG. 2.

[0071] Example 3 8 is a circuit diagram of an audio circuit 300C according to Example 3. In this example, N=2. A signal in S / PDIF (Sony Philips Digital Interface) format can be input to the audio circuit 300C as a digital audio signal.

[0072] Furthermore, two-channel (L channel and R channel) analog audio signals AL and AR can be input to the audio circuit 300C in a single-ended (unbalanced) manner.

[0073] When a digital audio source is connected, an S / PDIF signal is input to the first input pin P1.

[0074] When an analog sound source is connected, a single-ended analog audio signal AL of one channel (e.g., L channel) can be input to the first input pin P1, and a single-ended analog audio signal AR of another channel (e.g., R channel) can be input to the second input pin P2.

[0075] The internal circuit 320C includes Schmitt buffers B11 and B12, an S / PDIF circuit 322C, D / A converters 324L and 324R, output selectors SEL21 and SEL22, output buffers B21 and B22, and an analog processing circuit 330.

[0076] The S / PDIF circuit 322C and D / A converters 324L and 324R become active when an S / PDIF signal is input to input pin P1, and separate the received S / PDIF signal into L-channel and R-channel digital signals. The D / A converter 324L converts the L-channel digital signal into an analog signal, and the D / A converter 324R converts the R-channel digital signal into an analog signal. The rest of the configuration is the same as that of the internal circuit 320B in FIG. 7 (Example 2).

[0077] This audio circuit 300C can receive a serial digital audio signal or a single-ended analog audio signal via two input pins P1 and P2.

[0078] Example 4 9 is a circuit diagram of an audio circuit 300D according to Example 4. In this example, N=2. Pulse modulation signals DL and DR such as PDM signals (DSD signals) and PWM signals can be directly input to the audio circuit 300D as digital audio signals.

[0079] Furthermore, two-channel (L channel and R channel) analog audio signals AL and AR can be input to the audio circuit 300D in a single-ended (unbalanced) manner.

[0080] When a digital sound source is connected, pulse modulated signals DL and DR for the L and R channels can be input to the input pins P1 and P2, respectively.

[0081] When an analog sound source is connected, a single-ended analog audio signal AL of one channel (e.g., L channel) can be input to the first input pin P1, and a single-ended analog audio signal AR of another channel (e.g., R channel) can be input to the second input pin P2.

[0082] The internal circuit 320D includes Schmitt buffers B11 and B12, a decoder circuit 322D, D / A converters 324L and 324R, output selectors SEL21 and SEL22, output buffers B21 and B22, and an analog processing circuit 330.

[0083] The decoder circuit 322D becomes active when the pulse-modulated signals DL and DR are input to the input pins P1 and P2, and decodes the received pulse-modulated signals DL and DR. The D / A converters 324L and 324R convert the digital signals of the L channel and R channel into analog signals. The decoder circuit 322D and the D / A converters 324L and 324R may be replaced with analog low-pass filters. The other configurations are the same as those of the internal circuit 320B in FIG. 7 (Example 2).

[0084] This audio circuit 300D can receive a pulse-modulated digital audio signal or a single-ended analog audio signal via two input pins P1 and P2.

[0085] Example 5 In the first to fourth embodiments, an audio circuit including an analog processing circuit 330 has been described, but the present disclosure is also applicable to an audio circuit including a digital processing circuit 340. Fig. 10 is a circuit diagram of an audio circuit 300E according to a fifth embodiment. The audio circuit 300E can receive signals similar to those of the audio circuit 300A in Fig. 6, but includes a digital processing circuit 340 and an A / D converter 326 instead of the analog processing circuit 330 and the D / A converter 324.

[0086] The A / D converters 326L and 326R become active when analog audio signals are input to the input pins P1 to P4, and convert the analog audio signals into digital signals. Specifically, the A / D converter 326L has a differential input, and converts the L-channel differential analog signal AL P ,AL N The A / D converter 326R has a differential input, and converts the R-channel differential analog signal AR P ,AR N is converted into a digital signal.

[0087] The digital processing circuit 340 processes the outputs of the A / D converters 326L and 326R when analog signals are input to the input pins P1 to P4, and processes the output of the serial audio interface circuit 322E when digital signals are input to the input pins P1 to P4. For example, the digital processing circuit 340 may include output selectors SEL31 and SEL32 that select a digital audio signal when a digital audio signal is input to the input pins P1 to P4, and that select an output signal of the A / D converter 326 when an analog audio signal is input.

[0088] (Variation 1) In the second to fourth embodiments, the analog processing circuit 330 can be replaced with a digital processing circuit 340, as in the fifth embodiment.

[0089] (Variation 2) The configuration of the audio interface circuit 310 is not limited to that shown in Fig. 3. Figs. 11(a) and (b) are circuit diagrams of the audio interface circuit 310 according to Modification 2. Figs. 11(a) and (b) show only the portion corresponding to one pin. In the modification of Fig. 11(a), two bias resistors R1 # is the bias selector SEL1 # In FIG. 11(b), the bias selector SEL1 # Instead of switch SW1 # When an analog audio signal is input, switch SW1 # is turned on, and bias resistor R1 # and switch SW1 # via the bias voltage V BIAS is applied to input pin P#. Bias resistor R1 # and switch SW1 # may be interchanged. [Industrial Applicability]

[0090] The present disclosure relates to audio circuits. [Explanation of symbols]

[0091] 300 Audio Circuit 310 Audio Interface Circuit 312 Voltage divider circuit 314 buffer 320 Internal circuit 322A, 322B Serial Audio Interface Circuit 322C S / PDIF circuit 322D decoder circuit 324 D / A converter 326 A / D converter 330 Analog Processing Circuit 340 Digital Processing Circuit 404 Analog Sound Source 402 Digital Sound Source

Claims

1. 1. An audio circuit capable of receiving a digital audio signal including at least one signal or an analog audio signal including at least one signal, N (N≧1) input pins, each signal included in the digital audio signal being assigned to a corresponding one of the N input pins for input, and each signal included in the analog audio signal being assigned to a corresponding one of the N input pins for input; an audio interface circuit including N resistors corresponding to the N input pins, a first end of each resistor connected to a corresponding input pin, and a bias voltage applied to a second end of each of the N resistors when the audio circuit receives the analog audio signal; an internal circuit that processes the digital audio signal or the analog audio signal that has passed through the audio interface circuit; An audio circuit comprising:

2. 2. The audio circuit of claim 1, wherein the audio interface circuit is configured such that the second end of each of the N resistors is grounded when the audio circuit receives the digital audio signal.

3. 3. The audio circuit according to claim 2, wherein the audio interface circuit is configured such that, at the time of start-up of the audio circuit, the second end of each of the N resistors is grounded.

4. The internal circuit a D / A converter that is activated when the audio circuit receives the digital audio signal and converts the digital audio signal into an analog signal; an output selector that selects the output signal of the D / A converter when the audio circuit receives the digital audio signal, and selects the analog audio signal when the audio circuit receives the analog audio signal; an analog processing circuit that processes the output of the output selector; 4. An audio circuit according to claim 1, further comprising:

5. The internal circuit an A / D converter that is active when the audio circuit receives the analog audio signal and converts the analog audio signal into a digital signal; a serial audio interface circuit that processes the digital audio signal when the audio circuit receives the digital audio signal; an output selector that selects an output signal from the serial audio interface circuit when the audio circuit receives the digital audio signal, and selects an output signal from the A / D converter when the audio circuit receives the analog audio signal, and a digital processing circuit that processes an output of the output selector; 4. An audio circuit according to claim 1, further comprising:

6. 6. The audio circuit according to claim 1, wherein the bias voltage is half the power supply voltage of the audio circuit.

7. The audio interface circuit a voltage dividing circuit that divides the power supply voltage by 1 / 2; a buffer that receives the output voltage of the voltage divider circuit; N bias selectors corresponding to the N resistors; Equipped with each bias selector has a first input terminal connected to the output of the buffer, a second input terminal grounded, and an output terminal connected to the second end of a corresponding one of the N resistors, and is switchable between a first state in which conduction is established between the first input terminal and the output terminal, and a second state in which conduction is established between the second input terminal and the output terminal; 7. The audio circuit of claim 6, wherein when the audio circuit receives the analog audio signal, the N bias circuits are in the first state, and the output voltage of the buffer is applied as the bias voltage to the second end of each of the N resistors.

8. N=4, and the digital audio signal includes serial data, an LR clock, a bit clock, and a master clock; 8. The audio circuit according to claim 1, wherein the serial data, the LR clock, the bit clock, and the master clock are assigned to and input through four input pins.

9. N=3, and the digital audio signal includes serial data, an LR clock, and a bit clock; 8. The audio circuit according to claim 1, wherein the serial data, the LR clock, and the bit clock are input by being assigned to three input pins.

10. 8. The audio circuit according to claim 1, wherein the digital audio signal is a PWM signal.

11. 11. The audio circuit according to claim 1, wherein the analog audio signal is a differential signal.

12. 11. The audio circuit according to claim 1, wherein the analog audio signal is a single-ended signal.

13. 13. The audio circuit according to claim 1, wherein the audio circuit is monolithically integrated on a single substrate.

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