JPH08279786A - Signal transmitter - Google Patents

Abstract

PURPOSE: To exactly demodulate a transmission signal by demodulating a received signal to the digital signal of one bit corresponding to a regenerative clock signal by modulating the digital signal of one bit at a first exclusive OR gate corresponding to a clock signal at the 1/2 integer multiple of its sampling frequency. CONSTITUTION: On the transmission side, respective left and right channel sound signals converted to digital signals by an A/D converter 24 are applied to one input of exclusive OR gates GIL and GIR. Then, the clock signal at an 8-fold basic frequency fs at the 1/2 sampling frequency of the converter 24 is inputted from a clock generating circuit 25 to the other input. The digital sound signals of respective left and right channels are modulated by the clock signal, sent to an optical transmission part 26 later and transmitted from the optical transmission part 26 through optical paths KL and KR to an optical reception part 27. The optical signals received by the optical reception part 27 are turned to electric signals by clock reproduction 28 and demodulated to the analog acoustic signals of respective left and right channels through an integration circuit composed of a resistor 30 and a capacitor 31.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal transmission device which is preferably used for transmission of an acoustic signal between devices arranged remotely in an audio reproduction device.

[0002]

2. Description of the Related Art In a domestic or in-vehicle sound reproducing device, a remotely arranged device, for example, a main body which reproduces and amplifies an acoustic signal and a speaker transmit the acoustic signal as an optical signal. However, a configuration for reducing troublesome wiring arrangements is beginning to be used.

On the other hand, conventionally, in the transmission of digital audio signals, it has been general that 14-bit or 16-bit multi-bit signal data corresponding to the number of quantization bits is transmitted in parallel. In this case, the signal data to be transmitted is formatted by adding a synchronizing signal or the like by an interface such as a dedicated transmitting / receiving integrated circuit. Therefore, the acoustic signal transmission device having such a structure has a high manufacturing cost, a complicated structure, a large power consumption, and a problem in economical efficiency.

For this reason, in recent years, an economically excellent acoustic signal transmission device for converting an acoustic signal into a 1-bit digital signal and transmitting it has been disclosed, for example, in Japanese Unexamined Patent Publication No. 5-218981.
JP-A-5-130041 and JP-A-5-300
No. 102 publication. In this case, the receiving device can convert into an analog audio signal by a simple low-pass filter without using a special digital / analog converter. FIG. 3 shows a schematic configuration of the acoustic signal transmission device 1 of each of the related arts.

The analog audio signal input from the input terminal 3 of the transmitter 2 is sampled in the delta-sigma analog / digital converter 4 at a sampling frequency 16 times the sampling frequency fs (48 kHz) of the digital audio tape recorder. It is sampled, subjected to noise shaping, and converted into a digital audio signal having a quantization bit number of 1 bit. The digital acoustic signal is converted into an optical signal in the optical transmission unit 5 realized by including a light emitting diode or the like, and transmitted to the receiving device 6.

In the receiver 6, the optical signal is received by an optical receiver 7 including a photodiode and converted into an electric signal, and then a low-pass filter realized by an RC integrating circuit composed of a resistor 8 and a capacitor 9. After being integrated in 10, converted into an analog acoustic signal, it is led to an output terminal 11.

[0007]

In the above-mentioned prior art,
Since the optical signal deteriorated by the transmission is directly converted into the analog acoustic signal, if the optical signal is deteriorated due to the interruption of the optical path, for example, one bit input to the low-pass filter 10 is input. The digital audio signal suddenly becomes constant at a high level or a low level, and in the analog audio signal output from the output terminal 11, the deteriorated portion appears as noise, and the S / N becomes worse. is there.

An object of the present invention is to convert a signal to be transmitted into a 1-bit digital signal and transmit it by S /
It is to provide a signal transmission device capable of improving N.

[0009]

According to a first aspect of the present invention, there is provided a signal transmitting apparatus, wherein a transmitting apparatus is responsive to an converter for converting an input signal into a 1-bit digital signal and an output from the converter. And a light transmitting unit that emits light,
In a signal transmission device comprising an optical receiving unit that outputs a signal in response to the light, and a low-pass filter that integrates the output from the optical receiving unit and outputs as an analog signal, the transmitting device includes sampling of the converter. 1 / frequency
The receiver further includes a clock generation circuit that generates a clock signal at a frequency that is an integer multiple of 2, and a first exclusive OR gate that modulates the 1-bit digital signal with the clock signal. A clock regenerating circuit for regenerating the clock signal from the output of the receiving section, and a second exclusive OR gate for demodulating a 1-bit digital signal from the output of the optical receiving section by the regenerated clock signal and giving it to the low pass filter. And is further provided.

In the signal transmitting apparatus according to the second aspect of the present invention, the receiving apparatus may also sample the output of the optical receiving section at a frequency double that synchronized with the clock signal.
It is characterized by including a waveform shaping circuit for giving to the exclusive OR gate of.

[0011]

According to the invention of claim 1, the present invention is preferably implemented in transmission of an acoustic signal between devices arranged separately in the sound reproducing device, and in the transmitting device, the input signal is converted by the converter.
The digital signal of the bit is converted, and the optical transmission unit emits light in response to the output from the converter, and in the receiving device, the optical reception unit outputs the signal in response to the light and outputs the output. In a signal transmission device that integrates by a low-pass filter and outputs as an analog signal, thus making it possible to compensate for the deterioration of the signal that occurs due to the light being shielded in the signal transmission device that can greatly simplify the structure on the receiving side.

[0012] Specifically, on the transmitter side, the converter, when the input signal is an analog signal,
The input signal is converted into the 1-bit digital signal by sigma conversion or the like, and when the input signal is a digital signal, it is converted into the 1-bit digital signal by oversampling. The sampling frequency in this converter is an integral multiple of 1/2, for example, when the oversampling is performed at a sampling frequency of 16 times, a clock signal is generated at a clock generating circuit at a frequency of 8 times, and the clock signal is generated. By the above-mentioned 1 in the first exclusive OR gate.
The bit digital signal is modulated and transmitted from the optical transmitter.

Correspondingly, on the receiving device side, in the clock regenerating circuit, the clock signal is regenerated from the output of the optical receiving section, and the regenerated clock signal is used to generate the second signal.
1 from the output of the optical receiver by the exclusive OR gate of
Demodulate a bit digital signal.

Therefore, the optical signal from the transmitting device to the receiving device is blocked, and the optical signal is deteriorated.
Even if the output of the optical receiving section suddenly becomes a high level or a constant level of a low level, the 1-bit digital signal input from the second exclusive OR gate to the low-pass filter is the cycle of the clock signal. The high level and the low level are switched with each other, so that the analog signal output from the low pass filter becomes a signal whose input signal is equal to no signal.

In this way, the noise generated by the deterioration of the optical signal can be attenuated and the S / N can be improved.

According to a second aspect of the present invention, the receiving device is further provided with a waveform shaping circuit for sampling the output of the optical receiving section at a frequency double that synchronized with the clock signal. With this waveform shaping circuit, it is possible to correct the phase shift occurring in the output of the optical receiving section and give the output corresponding to the 1-bit digital signal to the second exclusive OR gate.

[0017]

FIG. 1 and FIG. 2 show an embodiment of the present invention.
The explanation is based on the following.

FIG. 1 is a block diagram showing an electrical configuration of an acoustic signal transmission device 21 according to an embodiment of the present invention. This acoustic signal transmission device 21 is implemented, for example, for a vehicle-mounted sound reproduction device. In that case, the transmission device 22 is embedded in a console or the like and reproduces a magnetic tape or receives a radio broadcast. The receiving device 23 is mounted on the main body of the device, while the receiving device 23 is mounted on a speaker mounted on a rear tray or the like.

In this acoustic signal transmitting device 21, roughly, the analog acoustic signals of the left and right channels input from the magnetic tape reproducing device to the input terminals P1L and P1R of the transmitting device 22 are converted into 1-bit digital acoustic signals. Converted,
The optical signal corresponding to the digital acoustic signal is the optical path KL,
It is transmitted to the receiving device 23 via each KR, demodulated into analog acoustic signals of left and right channels, and output terminal P
After being input to the power amplifier from 2L and P2R and amplified, it is given to the speaker to be sonicated.

In the transmitter 22, the input terminals P1L,
The analog audio signals of the left and right channels input from the P1R are delta-sigma type analog / digital converters 2.
In 4, the digital signal having a quantization bit number of 1 bit is converted and noise shaping is performed. The sampling frequency of the analog / digital converter 24 is, for example, 48 kHz, which is the sampling frequency of the digital audio tape recorder, as the basic frequency fs.
The frequency is selected to be six times, and the clock signal corresponding to the sampling frequency is input from the clock generation circuit 25.

The acoustic signals of the left and right channels converted into digital signals in the analog / digital converter 24 are applied to one input of exclusive OR gates G1L and G1R, respectively, and the exclusive OR of these is applied. A clock signal having a frequency eight times as high as the fundamental frequency fs, which is ½ the sampling frequency of the analog / digital converter 24, is input from the clock generation circuit 25 to the other input of the gates G1L and G1R. . In this way, the digital audio signals of the left and right channels are modulated by the clock signal and then input to the optical transmitter 26 including a light emitting element such as a light emitting diode. The acoustic signals of the left and right channels converted into optical signals by the optical transmitter 26 are transmitted to the optical receiver 27 of the receiving device 23 via the optical paths KL and KR, respectively.

The light receiving section 27 comprises a light receiving element such as a photodiode, and the light transmitting section 2
6 and the optical receiver 27, the optical paths KL,
The wavelengths at which the photoelectric conversion characteristics have a peak correspond to the light receiving / emitting elements forming a pair for forming KR, and thus interference between the optical paths KL and KR is prevented.

The optical signal received by the optical receiver 27 is input to the clock recovery circuit 28 and the waveform shaping circuit 29. In the clock recovery circuit 28, the left and right channels converted into electrical signals in the optical receiver 27. From the digital audio signal of, a clock signal having a frequency 16 times the fundamental frequency fs and a clock signal having a frequency 8 times the fundamental frequency fs are reproduced, and the waveform shaping circuit 29 and the exclusive OR gate G2L,
Output to one input of G2R.

The waveform shaping circuit 29 responds to the digital audio signals of the left and right channels from the optical receiving section 27 in response to the clock signal from the clock reproducing circuit 28, and outputs the signals from the optical receiving section 27 as will be described later. The phase shift occurring in the digital audio signal is corrected and output to the other inputs of the exclusive OR gates G2L and G2R, respectively. Outputs from the exclusive-OR gates G2L and G2R are demodulated into analog acoustic signals of left and right channels respectively in low-order low-pass filters FL and FR realized by an RC integrator circuit including a resistor 30 and a capacitor 31. , Output from the output terminals P2L and P2R.

FIG. 2 is a waveform diagram for explaining the operation of the acoustic signal transmission device 21 configured as described above. In this acoustic signal transmission device 21, the same operation is performed on the acoustic signals of both the left and right channels. Therefore, for simplification of the description, the following will be described only with respect to the left channel acoustic signal.

The analog / digital converter 24 samples the input analog acoustic signal at a sampling frequency of 16 fs, further performs noise shaping,
It is converted into a 1-bit digital audio signal as shown in FIG. This digital audio signal is output from the clock generation circuit 25 by the clock signal having the clock frequency of 8 fs as shown in FIG.
The signal is modulated as indicated by and is transmitted from the optical transmitter 26. As a result, the optical receiving unit 27 derives an output as shown in FIG. 2D, which is obtained by converting the input optical signal into an electric signal.

On the other hand, the clock recovery circuit 28 is shown in FIG.
A 64 fs basic clock signal as shown in (e) is sequentially divided by 1/2 to generate a 32 fs clock signal as shown in FIG. 2 (f), a 16 fs clock signal as shown in FIG. An 8 fs clock signal as shown in FIG. 2 (h) is created. The clock recovery circuit 28 has a rising edge of the output from the optical receiver 27 and 32 fs.
When the phase difference with the clock signal of No. 2 becomes a half cycle (180 °) or more of the clock signal of 32fs, reference symbols α1 and α
2, the 32 fs clock signal, 16 fs
And the 8 fs clock signal.

Therefore, by using the clock signal having the frequency of 16 fs, the waveform shaping circuit 29 shifts the phase as shown by reference numerals β1, β2, ... With respect to the input digital signal shown in FIG. 2 (d). Even if it occurs, it outputs a digital audio signal whose displacement is compensated as shown in FIG. 2 (i), which is almost the same as FIG. 2 (c).

This digital audio signal is demodulated in the exclusive OR gate G2L by the 8 fs clock signal from the clock recovery circuit 28 shown in FIG. 2 (h), and therefore the low-pass filter FL has the signal shown in FIG. 2 (j). The output is given by.

Here, as indicated by reference numeral γ1, even if the output from the optical receiving unit 27 is suddenly fixed to the Lo level due to the interruption of the optical path KL, the exclusive OR gate is used. From G2L, as shown in FIG. 3 (j), an output that repeats Hi level and Lo level in a cycle of 1/8 fs is derived corresponding to the 8 fs clock signal.

Therefore, when such an output is integrated by the low-pass filter FL, an output analog acoustic signal equal to that when the input analog acoustic signal is no signal is derived. In this way, the noise caused by the deterioration of the optical signal due to the interruption of the optical path KL is attenuated, and S
/ N can be improved. Further, in the case where the power level remains high, the power consumption in the related art increases, whereas the present invention can solve such a problem.

Although analog audio signals are input to the transmitting device 22 in the above-described embodiment, digital audio signals from, for example, a compact disc reproducing device or a digital audio tape recorder are directly input to the digital audio signals. By oversampling the audio signal, a digital audio signal having a quantization bit number of 1 bit may be created.

Further, exclusive OR gates G1L and G1R
The frequency of the clock signal to the analog / digital converter 24 and the frequency of the clock signal to the exclusive OR gates G2L and G2R corresponding thereto are
It may be an integral multiple of 1/2 of s.

[0034]

The signal transmission device according to the first aspect of the invention is
As described above, it is used for transmission between devices of a sound reproduction device, converts a signal to be transmitted into a 1-bit digital signal and transmits it as an optical signal, and the received signal is integrated by a low-pass filter to obtain an analog signal. In a signal transmission device capable of simplifying the structure of the receiving side,
The 1-bit digital signal is modulated by the first exclusive-OR gate with a clock signal that is an integral multiple of 1/2 of the sampling frequency, and the received signal is reproduced by the clock signal reproduced from the signal. The exclusive OR gate demodulates the 1-bit digital signal.

Therefore, even if the optical signal is deteriorated due to an interruption of the optical path from the transmitter to the receiver, one bit input from the second exclusive OR gate to the low-pass filter. Of the digital signal is switched between the Hi level and the Lo level in the cycle of the clock signal. Therefore, the output analog signal can be made a signal in which the input signal is equal to no signal, and the S / N can be improved. .

As described above, in the signal transmitting apparatus according to the second aspect of the present invention, the receiving apparatus is further provided with a waveform shaping circuit for sampling the output of the optical receiving section at a frequency twice that synchronized with the clock signal. .

Therefore, even if there is a phase shift in the output of the optical receiver, the shift can be corrected and the 1-bit digital signal on the transmitting side can be accurately restored.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electrical configuration of an acoustic signal transmission device according to an embodiment of the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the acoustic signal transmission device.

FIG. 3 is a block diagram showing a schematic configuration of a typical prior art acoustic signal transmission device.

[Explanation of symbols]

 21 acoustic signal transmission device 22 transmission device 23 reception device 24 analog / digital converter 25 clock generation circuit 26 optical transmission unit 27 optical reception unit 28 clock regeneration circuit 29 waveform shaping circuit FL low-pass filter FR low-pass filter G1L exclusive OR gate G1R Exclusive OR gate G2L Exclusive OR gate G2R Exclusive OR gate KL Optical path KR Optical path

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H04L 25/49

Claims (2)

[Claims] 1. A transmitter comprises a converter for converting an input signal into a 1-bit digital signal, and an optical transmitter radiating light in response to an output from the converter, and the receiver comprises: In a signal transmission device including an optical receiving unit that outputs a signal in response to light, and a low-pass filter that integrates the output from the optical receiving unit and outputs an analog signal, the transmitting device is a sampling frequency of the converter. Of 1
Further comprising a clock generation circuit that generates a clock signal at a frequency that is an integral multiple of / 2, and a first exclusive OR gate that modulates the 1-bit digital signal with the clock signal, A clock regenerating circuit for regenerating the clock signal from the output of the optical receiving section, and a second exclusive OR for demodulating a 1-bit digital signal from the output of the optical receiving section by the regenerated clock signal and giving the low pass filter. A signal transmission device further comprising a gate. 2. The receiving device further comprises a waveform shaping circuit for sampling the output of the optical receiving section at a frequency twice that of the clock signal and applying the sampled output to the second exclusive OR gate. The signal transmission device according to claim 1.