JPH0837502A - Audio signal transmitter - Google Patents

Abstract

PURPOSE:To simplify and miniaturize configuration and to reduce power consumption by converting a received optical signal to an electric signal to be changed corresponding to that optical signal and reproducing respective correspondent channel audio input signals based on this electric signal. CONSTITUTION:At a high-order digital sigma modulation circuit 3, the inputted audio signal is modulated to a one-bit quantized signal expressing a prescribed fine level change amount by an n-order [(n) is an integer >=2] digital sigma modulator and transmitted to a transmission circuit 4. Based on a one-bit L/R digital signal, the transmission circuit 4 drives and emits two high-luminance first and second LED corresponding to respective channels. At a light receiving circuit inside a reception circuit 5L, the optical signal from the first LED is received by a first photodiode, converted into a one-bit electric signal to be changed corresponding to the optical signal, and transmitted to an amplifier circuit. The digital signal from the reception circuit 5L is transmitted to a waveform shaping circuit 6L and a low-pass filter 7L, demodulated to an analog audio signal and reproduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio signal transmission device for transmitting an audio signal to a speaker or the like by optical transmission.

[0002]

2. Description of the Related Art In recent years, the development and research of devices for processing digital audio signals have been actively conducted. Along with this, digital audio signal transmission technology for connection between devices has been extensively studied.

Conventionally, as an audio signal transmission device, an analog type device which FM-modulates an audio signal and optically transmits it, and a digital type device which A / D converts the audio signal and optically transmits it are known. However, in the case of the analog type, since the dynamic range is about 60 to 70 dB, it is not satisfactory in reproducing music. Further, even in the case of the digital type, there is a problem that the structure of the receiving side becomes complicated and the size becomes large as a whole.

Therefore, an audio signal transmission device having a large dynamic range and a simple structure on the receiving side has been proposed (for example, see Japanese Patent Laid-Open No. 5-130041). According to this, the audio input signal is modulated into a 1-bit digital audio signal representing a predetermined minute level change amount by the Nth-order delta-sigma modulator every time a minute unit time elapses. The modulated digital audio signal is converted into a digital optical signal by an optical signal transmitter and then transmitted to a receiver. When the receiver receives the transmitted digital optical signal, it is converted into an analog audio signal by the audio signal converter and reproduced. For this reason, the dynamic range becomes large, and since a 1-bit digital signal is transmitted and received between the transmitting and receiving sides, the audio input signal is faithfully reproduced without complicating the configuration on the receiving side.

[0005]

However, according to the above-mentioned conventional audio signal transmitting apparatus, when the stereo 2 channel audio signal is L / R channel multiplex-transmitted, the L signal is received and then the L signal is transmitted.
A separate means for determining the / R channel is required. In addition to this means, DAI (Digital Audio Interfa
ce) must be separately provided on the sending side and the receiving side.

Furthermore, the use of DAI requires a transmission rate of 6 Mbps, which imposes severe performance limitations on the light emitting device and the light receiving device. However, there is a problem in that the cost required to satisfy this restriction is much larger than the cost required to simplify the D / A conversion.

[0007]

In order to solve the above-mentioned problems, the present invention provides a high-order delta-sigma modulation of an N (N is an integer of 2 or more) channel audio input signal for each 1-bit quantum. Delta sigma modulation means for outputting a signal to be digitized, N light emitting means (for example, a light emitting diode, etc.) that are driven based on the 1-bit quantized signal, and emit optical signals having different wavelengths, and the corresponding light emission. Based on the electric signals from the N light receiving means (for example, PIN photodiodes) for receiving an optical signal from the means and converting each to a 1-bit electric signal that changes according to the received optical signal, and the electric signal from each light receiving means. And N number of reproducing means for reproducing the corresponding channel audio input signal.

According to a second aspect of the present invention, in the configuration of the first aspect, the reproducing means is a waveform shaping means for shaping the waveform of the electric signal from each light receiving means, and a low pass for passing the output of the waveform shaping means to a low frequency band. It has a band-passing means, and the waveform shaping means, the low-band passing means, and the light receiving means are integrally formed.

[0009]

According to the structure of the first aspect, the N-channel audio input signal is high-order delta-sigma modulated by the delta-sigma modulating means and output as a 1-bit quantized signal.

Based on the above 1-bit quantized signal, N
Each of the light emitting means is driven. As a result, each light emitting means emits an optical signal having a predetermined wavelength toward the corresponding light receiving means based on the corresponding channel signal. The transmission operation is performed as described above.

Upon receiving the optical signal from the corresponding light emitting means, each light receiving means generates a 1-bit electric signal that changes according to the received optical signal and sends it to the corresponding reproducing means. Since this electric signal corresponds to each channel audio signal, each reproducing means reproduces only the corresponding channel audio signal. The reception and reproduction operations are performed as described above.

According to the structure of claim 2, the waveform shaping means,
The low-pass passage means and the light receiving means are integrally formed. Therefore, in addition to the effects of the first aspect, the integration density is increased, the overall configuration of these means is simplified and downsized, and the total power consumption is also reduced.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS.

This embodiment exemplifies an audio signal transmission device for transmitting a stereo audio signal of 2 channels. However, the present invention is not limited to the number of channels being two, and can be applied to the case of transmitting audio signals of two or more channels.

The two-channel stereo audio signal is
It is serially output from the audio reproduction device 1. The audio reproducing device 1 has a function of reproducing an audio recording medium such as a CD (Compact Disk) and a magnetic tape, and / or a tuner function. This stereo audio signal is sent to the preamplifier 2, where it is subjected to processing such as amplification and preemphasis if necessary, and then sent to the high-order delta-sigma modulation circuit 3 (delta-sigma modulation means).

In the high-order delta-sigma modulation circuit 3, a predetermined n-th order (n is an integer of 2 or more) delta-sigma modulator (not shown) is applied to the input audio signal at predetermined time intervals. Is modulated into a 1-bit L / R digital signal (1-bit quantized signal) representing the minute level change amount of and is sent to the transmission circuit 4.

That is, in the high-order delta-sigma modulation circuit 3, the analog voice input signal is converted into a 1-bit digital voice signal and the voice band (20 Hz to 2 Hz).
After the quantization noise in (0000 Hz) is sufficiently reduced, 1
It is output as a bit L / R digital signal. In this case, in this embodiment, the sampling frequency, that is, the transmission rate is set to about 768 kHz. This is the current 16-bit digital audio (sampling frequency is 48
This is to obtain a level equivalent to (kHz). That is, the amount of information =
(Number of bits) x (Sampling frequency) = 16 (bits) x 4
The above 768 kHz is calculated from 8 (kHz) = 1 (bit) × 768 (kHz).

In the high-order delta-sigma modulation circuit 3, the higher the order of feedback, the higher the capability of quantization noise shaping, but the more unstable the circuit operation becomes. Currently, the return order is 7
The following items are available, but according to the present embodiment, even items of 7th order or higher can be used.

The transmitting circuit 4 is composed of an LED driving circuit and a light emitting circuit (neither is shown).

The LED (Light Emitting D) in the transmitter circuit 4
The drive circuit is composed of a switching element such as a transistor, and based on the 1-bit L / R digital signal, two high-brightness first and second LEDs (neither shown) corresponding to each channel. Drive to make it emit light. That is, the first and second LEDs are turned ON / OF according to the number of pulses of the audio 1-bit signals L and R, respectively.
F In this embodiment, the first LED is for the L channel (left channel) and has the wavelength of infrared light, while the other second LED is for the R channel (right channel) and the wavelength of red light. The optical signals having these wavelengths are respectively emitted to the photodiodes (light receiving means) described later. As a result, optical transmission is performed.

The optical signal from the first LED is received by the receiving circuit 5L.
While being sent to (light receiving means), the optical signal from the second LED is sent to the receiving circuit 5R (light receiving means). Receiver circuit 5L
Each of 5R is composed of a light receiving circuit having first and second photodiodes, an amplifier circuit, and a limiter circuit (none of which is shown).

In the light receiving circuit in the receiving circuit 5L, the first LE
The optical signal from D is received by the first photodiode, converted into a 1-bit electric signal that changes according to the optical signal, and sent to the amplifier circuit. Then, after being amplified by an amplifier circuit, it is sent to a limiter circuit, the level of which is limited and output as a 1-bit digital signal. Similarly, in the light receiving circuit in the receiving circuit 5R, the optical signal from the second LED is received by the second photodiode, converted into a 1-bit electric signal that changes according to the optical signal, and sent to the amplifier circuit. Then, after being amplified by an amplifier circuit, it is sent to a limiter circuit, the level of which is limited and output as a 1-bit digital signal.

The first and second photodiodes are
The PIN type is preferable in terms of response speed, but it is generally manufactured so that the spectral sensitivity characteristic can correspond to infrared light, and infrared light can be sharply shielded against the wavelength of red light. Since it is difficult to obtain the one having the characteristic, in this case, the reception (interference) of the optical signal from the other LED which does not correspond can be avoided by using the optical filter. When transmitting on multiple channels, it is effective to use the optical filter.

The 1-bit digital signal from the receiving circuit 5L is sent to a waveform shaping circuit 6L (waveform shaping means) where noise such as jitter is removed, and then a low pass filter (LPF) which is a low pass means. ) It is sent to 7L. The low-pass filter 7L is a low-order LPF having a simple structure, in which the 1-bit digital signal is demodulated into an analog audio signal which is a base signal of the L channel and sent to the audio amplifier 8L. In the audio amplifier 8L, the demodulated analog audio signal is amplified and then sent to the speaker 9L (reproducing means) where it is reproduced.

Similarly, the 1-bit digital signal from the receiving circuit 5R is sent to the waveform shaping circuit 6R (waveform shaping means), where noise such as jitter is removed, and then low-pass means which is low-pass means. It is sent to the filter (LPF) 7R. The low-pass filter 7R is a low-order LP with a simple structure.
F, where the 1-bit digital signal is demodulated into an analog audio signal which is a base signal of the R channel and sent to the audio amplifier 8R. The audio amplifier 8R amplifies the demodulated analog audio signal, and then the speaker 9R
It is sent to (reproduction means) and reproduced here.

As described above, according to this embodiment, the stereo audio signal is delta-sigma modulated into the 1-bit L / R digital signal by the high-order delta-sigma modulation circuit 3, and 1
First and second L without being multiplexed to the channel
Two channels of light are optically transmitted from the ED to the first and second photodiodes. Therefore, the encoder circuit, the decode circuit, the interface circuit for wireless transmission on the transmission side / reception side, etc. necessary for multiplexing and transmitting on one channel are not required, which simplifies the circuit configuration and reduces the manufacturing cost. Can be realized. As described above, since the interface circuit is unnecessary, the power consumption is reduced from several tens of milliamperes to several milliamperes, so that it is possible to save power, and it is also possible to use a small button battery or the like as an operating power supply.

Further, according to the configuration of this embodiment, the transmission can be performed without increasing the transmission rate of the transmission line as in the prior art. In addition, the transmission of the audio signal is performed in two channels, which requires two light-emitting devices / light-receiving devices and the like. The cost required for this is that the interface circuit and the like are transmitted to the transmitting side and the receiving side. It is much cheaper than the cost of installation.

Furthermore, since it is not necessary to increase the transmission rate, the optical transmission distance and the tolerances for optical axis alignment and the like increase, which is imposed on each component connected after the first and second photodiodes. The requirement for performance is relaxed and the circuit configuration can be certainly simplified, so that the cost can be reduced as a whole.

By the way, recent CD / MD (Mini Disk
) Etc. for reproducing a digital audio reproducing apparatus 10
In many cases, a 1-bit converter is built in, and as shown in FIG. 2, for example, it has an audio reproduction device 10a and a high-order delta-sigma modulation circuit 10b. In this case, since the analog signal is output after D / A conversion in the high-order delta sigma modulation circuit 10b, the high-order delta sigma modulation circuit 10b uses the 1-bit L of the sampling frequency near 768 kHz. It is easy to output the / R digital signal (1-bit quantized signal) before the low-pass filter (not shown).

Therefore, in the case of the digital audio reproducing apparatus 10, the 1-bit L / R output as described above is used.
The digital signal can be transmitted to the above-mentioned receiving circuits 5L and 5R through the wireless transmission adapter 11 having the same function as that of the above-mentioned transmitting circuit 4.

As described above, in the case of the digital audio reproducing apparatus having the built-in 1-bit converter, the 1-bit L / R digital signal (1
Bit quantized signal) to a high-order delta-sigma modulation circuit 10b
Since it can be easily output in front of the low-pass filter inside, the transmission circuit can be directly connected to the wireless transmission adapter 11 in which the transmission circuit is adapted. Therefore, it is highly portable, the configuration can be simplified, the integration rate of the component parts can be improved, and the size can be reduced, the cost can be saved, and the power consumption can be saved.

The receiving circuits 5L and 5R, the waveform shaping circuits 6L and 6R, and the LPF 7 provided on the receiving side are provided.
L and 7R are integrally formed to form a wireless reception adapter 1
Since it can be set to 2, the configuration can be simplified, the integration rate can be improved, the cost can be reduced, and the power consumption can be reduced (it can be suppressed to several milliamperes or less).

In this case, a small button battery (CR2016 class battery) or the like can be used to supply the operating power source in the case of being integrated, and in this case, for more than ten hours,
It becomes possible to operate continuously, and as a compact wireless optical receiving adapter, it can be connected to the auxiliary (AUX) input terminal 13a of the audio amplifying / reproducing device 13 of an existing audio device or the like to enable wireless transmission with a portable device. Become.

This is particularly effective when connected to a car audio device, such as a portable CD player or MD player, and can meet the needs that are currently occurring. In this case, the transmitting side also needs an adapter for connecting to a portable CD player, an MD player, or the like, but the wireless transmitting adapter 11 described above may be used.

Here, for comparison with the present embodiment, FIG.
An audio signal transmission device having the above configuration will be described below. The members having the same functions as those in the above embodiment are designated by the same reference numerals, and the description thereof will be omitted.

In the configuration of FIG. 4, an L / R multiplexing circuit A and a DAI transmitter B are provided between the high-order delta sigma modulation circuit 3 and the transmission circuit 4 in order to multiplex into one channel. The point that the DAI receiver C and the L / R separation circuit D are provided between the waveform shaping circuit 6 and the LPFs 7L and 7R, and that the transmission circuit 4 and the reception circuits 5L and 5R transmit one channel. 1 is different from the configuration in FIG. Since these circuits are separately provided, according to the configuration of FIG. 4, it is necessary to transmit the 1-bit L / R digital signal at the transmission rate of 6 Mbps. This is about one digit larger than the transmission rate of 0.768 Mbps in the present embodiment, so that the performance limitation required for the transmission device, the reception device, and the peripheral circuit parts becomes very severe, and this limitation is also imposed. In order to satisfy the above requirement, the cost is increased, and as a whole, the cost is significantly increased. According to the configuration of the above-described embodiment, it is clear that all these problems have been solved.

[0037]

As described above, according to the invention of claim 1, N
(N is an integer of 2 or more) Channel audio input signals are subjected to high-order delta sigma modulation to output 1-bit quantized signals, and delta-sigma modulation means, which are driven based on the 1-bit quantized signals, respectively. N light emitting means for emitting different optical signals, and light signals received from the corresponding light emitting means, and change according to the received optical signal 1
It has a configuration including N light receiving means for converting each to a bit electric signal, and N reproducing means for reproducing an audio input signal for each corresponding channel based on the electric signal from each light receiving means. There is.

Therefore, since it is not multiplexed to one channel as in the conventional case, an encoding circuit, a decoding circuit, and an interface circuit for wireless transmission on the transmitting side / receiving side, which are necessary when multiplexing on one channel, are unnecessary. It is possible to surely realize cost reduction.

Further, in the prior art, the high transmission rate of 6 Mbps required when using the above interface circuit imposes severe performance limitation on the light emitting device / light receiving device. , Transmission can be performed without increasing the transmission rate of the transmission path.

In addition, the transmission of the audio signal is performed in N channels, which requires N light emitting devices / light receiving devices. The cost required for this is that the conventional interface circuit, etc. In addition, the cost can be much lower than the cost of separately installing on the receiving side.

Furthermore, since it is not necessary to increase the transmission rate, the optical transmission distance and the tolerances such as optical axis alignment become large, and the performance requirements imposed on each component after the light receiving means are alleviated, and the circuit configuration is reduced. Since it can be simplified, there is an effect that the cost can be reduced as a whole.

As described above, in the invention of claim 2, in the structure of claim 1, the reproducing means outputs the waveform shaping means for shaping the waveform of the electric signal from each light receiving means and the output of the waveform shaping means. It has a low-pass passage means for passing the low-pass, and the waveform shaping means, the low-pass means, and the light receiving means are integrally formed.

Therefore, in addition to the effect of the first aspect, there is an effect that the integration density is increased, the overall structure of these means can be simplified and downsized, and therefore the total power consumption can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of an audio signal transmission device of the present invention.

FIG. 2 is an explanatory diagram showing a case where a digital audio playback device with a built-in 1-bit converter and a wireless transmission adapter are connected.

FIG. 3 is an explanatory diagram showing a wireless reception adapter in the case of integrating the components on the reception side.

FIG. 4 is a block diagram showing a difference between the present invention and an audio signal transmission device in the case of multiplexing with one channel.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Audio reproduction device 2 Preamplifier 3 Higher-order delta sigma modulation circuit (delta sigma modulation means) 4 Transmission circuit (light emission means) 5L Reception circuit (light reception means) 6L Waveform shaping circuit (waveform shaping means, reproduction means) 7L Low pass filter (low Band-passing means, reproducing means) 9L speaker (reproducing means) 10 digital audio reproducing device 11 wireless transmission adapter (light emitting means) 12 wireless receiving adapter (light receiving means, reproducing means)

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location H04B 10/06 H03M 3/02 9382-5K H04B 14/06 A H04H 5/00 302

Claims (2)

[Claims] 1. A delta-sigma modulating means for high-order delta-sigma modulating an N-channel (N is an integer of 2 or more) channel audio input signal to output a 1-bit quantized signal, and based on the 1-bit quantized signal. Each driven,
N light emitting means for emitting optical signals having different wavelengths, and N light receiving means for receiving the optical signals from the corresponding light emitting means and converting the light signals into 1-bit electric signals that change according to the received optical signals. And an N number of reproducing means for reproducing the corresponding channel audio input signal based on an electric signal from each light receiving means. 2. The reproducing means includes a waveform shaping means for shaping the waveform of an electric signal from each light receiving means, and a low-pass means for passing the output of the waveform shaping means in a low frequency range. The audio signal transmission device according to claim 1, wherein the means, the low-pass means, and the light receiving means are integrally formed.