JP2003152461A - Photodetecting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photodetecting circuit which can be suitably used as a wireless headphone or the like and which can prevent a composite output signal from suffering a loss even when a plurality of photodetectors are disposed isolatedly from each other. SOLUTION: A plurality of photoelectric converters respectively receive light signals and convert the signals into electric signals, and output the signals to output terminals. The output terminals of the photoelectric converters are connected to a common connecting point, and the output signals of the respective converters are combined. The signal of a predetermined frequency is extracted from the combined output signal via a filter circuit. Since the output signals of the converters are output from the drain terminals of source grounding circuits, a transmission loss between the converters and the filter circuit can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light receiving circuit for receiving an optical signal, and more particularly to a light receiving circuit suitable for cordless headphones and the like.

[0002]

2. Description of the Related Art Cordless headphones used together with a television receiver and an audio device (hereinafter referred to as "AV device") are mounted on a transmitter connected to the AV device and a user's head. It consists of a receiver attached to the headphone unit. The transmitter converts an audio signal or the like output from the AV device into an optical signal such as infrared rays and transmits the optical signal. The receiver receives the optical signal transmitted from the transmitter, performs necessary signal processing, and supplies an audio signal to, for example, the left and right headphone units.

The light receiving circuit provided in the receiver includes a light receiving element such as a photodiode and converts the transmitted optical signal into an electric signal. Where commonly used PIN
Since light receiving elements such as photodiodes have a narrow directivity,
In order to realize ideal directivity, a headphone unit is provided with a plurality of light receiving elements.

[0004]

As a circuit for attaching a plurality of light receiving portions to a headphone unit and synthesizing the outputs thereof, an electric signal output from the light receiving element is taken out by a source follower circuit of an FET and is required by a bandpass filter. A method is known in which only a certain band is extracted and combined by a mixer composed of a combined resistor. However, in this method, since the output signal in the mixer using the combined resistance is greatly attenuated, it is difficult to extract the combined signal having a sufficient output level.

On the other hand, as another method, there is a method in which a plurality of light receiving elements are provided in parallel in terms of circuit configuration, and an example thereof is described in JP-A-64-23583. However, in this method, transmission loss occurs when a plurality of light receiving elements are arranged apart from each other. Therefore, due to the circuit configuration, the plurality of light receiving elements have to be arranged close to each other to some extent. as a result,
There is a problem that a position where the light receiving element is provided on the headphone unit is restricted, and a satisfactory directivity cannot be realized.

The present invention has been made in view of the above points, and can be suitably used for wireless headphones and the like, and even when a plurality of light receiving elements are arranged apart from each other, the loss of the combined output signal is obtained. An object of the present invention is to provide a light receiving circuit capable of preventing the above.

[0007]

According to one aspect of the present invention, in a light receiving circuit, a plurality of photoelectric conversion circuits whose output terminals are connected to a common connection point and a plurality of photoelectric conversion circuits which are connected to the common connection point and pass a predetermined frequency are provided. A filter circuit having a band, and each of the photoelectric conversion elements includes a light receiving element and an FET (field effect transistor) having a gate connected to the light receiving element.

According to the light receiving circuit configured as described above, each of the plurality of photoelectric conversion circuits receives an optical signal, converts it into an electric signal, and outputs the electric signal to each output terminal. Since the output terminals of the plurality of photoelectric conversion circuits are connected to the common connection point, the output signals from the photoelectric conversion circuits are combined. A signal having a predetermined frequency is extracted from the combined output signal by the filter circuit.

In one mode of the above light receiving circuit, the FET
Has a source grounded and a drain connected to the common connection point as the output terminal.

According to this aspect, since the output signal from each photoelectric conversion circuit is output from the drain terminal of the source-grounded circuit with a relatively high impedance, the transmission loss between the photoelectric conversion circuits and between the filter circuits is small. .

In another mode of the above light receiving circuit, the filter circuit has an inductor and a capacitor connected to the common connection point.

According to this aspect, the filter circuit is configured as a resonance circuit including the inductor and the capacitor connected to the drain terminal of the photoelectric conversion circuit.

In still another mode of the above light receiving circuit,
The photoelectric conversion element receives an optical signal obtained by photoelectrically converting a predetermined modulation signal, and the filter circuit has the frequency of the modulation signal as a pass band.

According to this aspect, a modulated signal of an original signal such as a voice signal is transmitted as an optical signal. The photoelectric conversion circuit converts the optical signal into an electric signal, and the filter circuit extracts the frequency component of the modulation signal. This allows optical transmission of original signals such as audio signals.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic configuration of a wireless headphone system using a light receiving circuit according to an embodiment of the present invention. As shown, the wireless headphone system includes a transmitter 10 and a receiver 20.

The transmitter 10 receives the audio signal 6 output from the AV equipment, converts the audio signal 6 into an optical signal 15, and converts the optical signal 15 into a receiver 20.
And is provided with a modulation circuit 11 and a light emitting unit 12. The modulation circuit 11 performs a predetermined modulation process on the input audio signal 6 and outputs a modulated signal 7 as a light emitting unit 1.
Supply to 2. The audio signal 6 output from the AV device is
Since the L-channel and R-channel signals are included, the modulation circuit 11 modulates the audio signal of each channel with a different carrier, and supplies the modulated signal 7 to the light emitting unit 12.

The light emitting section 12 is composed of one or a plurality of light emitting diodes or the like, and is driven by the modulation signal 7 output from the modulation circuit 11 to emit light. As a result, the modulated signal 7 is converted from the electric signal into the optical signal 15, and the transmitter 1
It is sent from 0.

On the other hand, the receiver 20 receives the optical signal 15 and converts it into an electric signal, and comprises a light receiving portion 21, a demodulation circuit 22, and left and right headphone units 23 and 24. The optical signal 15 sent from the transmitter 10 is received by the light receiving unit 21. The light receiving unit 21 includes a photoelectric conversion element such as a PIN photodiode as described later, converts the optical signal 15 into the audio signal 8 which is an electric signal, and supplies the audio signal 8 to the demodulation circuit 22.

The demodulation circuit 22 performs a predetermined demodulation process on the audio signal 8 and supplies it as a demodulated signal 9 to the left and right headphone units 23 and 24. The demodulation processing performed by the demodulation circuit 22 in the receiver 20 is performed by the transmitter 10
It corresponds to the modulation processing performed by the modulation circuit 11 in the inside.

The headphone units 23 and 24 are provided so as to be located near the user's ear on the headphone worn on the user's head and reproduce the demodulated signal 9.
In this way, the audio signal output from the AV device is transmitted as the optical signal 15 from the transmission unit 10 to the reception unit 20, and is reproduced on the headphone unit.

In the above example, the modulation circuit 11 modulates the L channel and R channel audio signals 6 with different carriers, but by using digital communication, the signals of both channels are modulated with one carrier. The modulated signal 7 can be supplied to the light emitting unit 12.

FIG. 2 shows a circuit configuration of the light receiving section 21 using the light receiving circuit of the present invention. As shown in the figure, the light receiving section 21 is roughly classified into two photoelectric conversion circuits 38 and a filter circuit 3.
4 and. The photoelectric conversion circuit 38 is composed of a pair of PIN photodiode 31 and FET 32. The optical signal 15 transmitted from the transmitter 10 is received by the photodiode 31. The FET 32 constitutes a grounded source circuit and outputs the electric signal output from the photodiode 31 from the drain terminal with a relatively high impedance.

The filter circuit 34 is a resonance circuit having an inductor 35 and a capacitor 35. Two FET3
The drain terminal of 2 is connected to the terminal between the inductor 35 and the capacitor 36 in the filter circuit 34. F
Since the ET32 constitutes a source grounded circuit, the output impedance from the drain terminal and the filter circuit 34
Resonance is obtained by the inductor 35 and the capacitor 36 therein, and only a signal in a predetermined frequency band is output as the electric signal 8. The resonance frequency of the filter circuit 34 is matched with the frequency of the modulation signal 7 output from the modulation circuit 11 in the transmitter 10.

According to the circuit configuration of the present invention, since the output signal from the photoelectric conversion circuit 38 is not mixed by the combined resistance, the output loss due to the combined resistance does not occur. In addition, PI
Even if the N photodiode 31 and the filter circuit 34 are arranged apart from each other on the headphones, the transmission loss is smaller than in the case where the photodiode outputs are combined and transmitted as in the prior art. Therefore, even when the PIN photodiode 31 is separated and arranged on the headphone unit in order to obtain sufficient directivity, the loss of the output signal can be suppressed.

A user who uses cordless headphones often moves or changes his / her posture even when wearing the headphones, so that the optical signal 15 from the transmitter 10 cannot be received if the directivity of the receiver 20 is narrow. Cases can arise. However, by using the light receiving circuit of the present invention, it is possible to attach a plurality of light receiving elements such as photodiodes to various positions of the headphone without fear of loss of output signals, so that an ideal directivity of 360 degrees can be obtained. It is possible to arrange each light receiving element on the headphones so as to obtain.

In the example of FIG. 2, the light receiving section 21 is composed of two photoelectric conversion circuits 38, but the light receiving section 21 may be structured to include three or more photoelectric conversion circuits 38. . In that case, a desired number of photoelectric conversion circuits 38 may be added in parallel to the two photoelectric conversion circuits 38 of FIG.

[0028]

As described above, according to the light receiving circuit of the present invention, the loss of the output signal can be combined to be extremely small. Therefore, it is effective for wideband transmission such as infrared digital communication, and particularly suitable for infrared digital cordless headphones.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a wireless headphone system to which a light receiving circuit of the present invention is applied.

FIG. 2 is a circuit configuration diagram of a light receiving unit shown in FIG.

[Explanation of symbols]

10 transmitter 11 Modulation circuit 12 Light emitting part 20 receiver 21 Light receiving part 22 Demodulation circuit 23, 24 headphone unit 34 Filter circuit 38 Photoelectric conversion circuit

Continued front page    (72) Inventor Kazumi Shitara             1105 Nikko Niigata, Tendo City, Yamagata Prefecture             Tohoku Pioneer Corporation F-term (reference) 5D005 BB11 BB17                 5J069 AA01 AA21 AA56 CA00 FA00                       HA09 HA19 HA25 HA29 HA32                       HA33 HA44 KA41 KA53 KA55                       KA63 MA19 MA21 SA06 SA08                       TA01                 5J092 AA01 AA21 AA56 CA00 FA00                       HA09 HA19 HA25 HA29 HA32                       HA33 HA44 KA41 KA53 KA55                       KA63 MA19 MA21 SA06 SA08                       TA01 UL02                 5J500 AA01 AA21 AA56 AC00 AF00                       AH09 AH19 AH25 AH29 AH32                       AH33 AH44 AK41 AK53 AK55                       AK63 AM19 AM21 AS06 AS08                       AS09 AT01 LU02

Claims (4)

[Claims] 1. A plurality of photoelectric conversion circuits whose output terminals are connected to a common connection point, and a filter circuit which is connected to the common connection point and has a pass band of a predetermined frequency, each of the photoelectric conversion elements. Is a light receiving circuit having a light receiving element and an FET having a gate connected to the light receiving element. 2. The light receiving circuit according to claim 1, wherein the FET has a source grounded and a drain connected as the output terminal to the common connection point. 3. The light receiving circuit according to claim 1, wherein the filter circuit has an inductor and a capacitor connected to the common connection point. 4. The photoelectric conversion element receives an optical signal obtained by photoelectrically converting a predetermined modulation signal, and the filter circuit has a frequency of the modulation signal as a pass band. The light receiving circuit according to any one of items.