Receiving circuit and electronic apparatus for optical communication

• US 20060008280A1
• Filed: 07/07/2005
• Published: 01/12/2006
• Est. Priority Date: 07/09/2004
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Yokogawa, Naruichi, Nishino, Takeshi
• Granted Patent: US 7,460,792 B2
• Time in Patent Office: Days
• US Class Current: 398/202
• CPC Class Codes: H04B 10/114 Indoor or close-range type systems

Abstract

In an optical communication-use receiving circuit of the present invention, the pulse width of the received pulse which is a binary signal corresponding to the signal optical pulse is specified by using an integration circuit and a trigger generating circuit. If the pulse width of the received pulse is not shorter than a predetermined value, a signal having a fixed pulse width is outputted as an output signal from a one-shot pulse generating circuit, so that a pulse having a constant pulse width corresponding to the specified communication speed is outputted. Accordingly, if the pulse width deriving from the signal optical pulse is larger than a certain value, the communication is deemed as a low-speed communication, and a pulse having a constant pulse width corresponding to the communication speed is outputted. As a result, it is possible to realize a small-size receiving circuit and a small-size electronic device which require no external switching-over terminal.

Claims

1. A receiving circuit, for use in an optical communication, from which an output signal is outputted in accordance with a signal optical pulse incident to a light-receiving element,

the receiving circuit comprising:

a variable output circuit for (I) detecting a pulse width of the signal optical pulse, (II) determining a pulse width of the output signal in accordance with the pulse width of the signal optical pulse, and (III) outputting the output signal.

2. The receiving circuit as set forth in claim 1, wherein:

the variable output circuit includes a first pulse generating circuit generating a received pulse by comparing an electric signal converted from the signal optical pulse with a threshold, the received pulse being a digital signal; and

either the received pulse generated by the first pulse generating circuit or a pulse having a different pulse width from that of the received pulse is selectively outputted as an output signal, in accordance with the pulse width of the signal optical pulse.

3. The receiving circuit as set forth in claim 2, wherein:

the variable output circuit includes a second pulse generating circuit for generating a signal having a predetermined pulse width corresponding to a low-speed communication; and

if it is judged that a pulse width of an output from the first pulse generating circuit exceeds a predetermined value, a signal generated by the second pulse generating circuit is outputted as the output signal, instead of outputting the received pulse.

4. The receiving circuit as set forth in claim 3, wherein:

the variable output circuit includes (I) a trigger generating circuit for generating a trigger signal when a pulse generating time of the first pulse generating circuit exceeds a first predetermined period, and (II) a timer circuit for generating a pulse having a second predetermined pulse width, in response to the trigger signal from the trigger generating circuit;

if the timer circuit outputs no pulse, a pulse outputted from the first pulse generating circuit is outputted as the output signal; and

if the timer circuit outputs a pulse, a pulse outputted from the second pulse generating circuit is outputted as the output signal.

5. The receiving circuit as set forth in claim 3, wherein:

the first pulse generating circuit includes a one-shot pulse generating circuit that receives the received pulse and maintains the pulse width of the output signal at a constant value.

6. The receiving circuit as set forth in claim 3, wherein the first pulse generating circuit includes a delay circuit to which the received pulse is inputted.

7. The receiving circuit as set forth in claim 5, further comprising a delay circuit connected to an output of the one-shot pulse generating circuit.

8. The receiving circuit as set forth in claim 4, wherein:

a length of the first predetermined period is set between a pulse width of the output pulse from the second pulse generating circuit and a pulse width of the output pulse from the first pulse generating circuit.

9. The receiving circuit as set forth in claim 8, wherein the first predetermined period is between 521 n sec. and 1.41 p sec.

10. The receiving circuit as set forth in claim 4, wherein the second predetermined period is equal to or longer than a maximum interval between a pulse and another pulse.

11. The receiving circuit as set forth in claim 10, wherein the second predetermined period is 1.04 m sec. or longer.

12. The receiving circuit as set forth in claim 4, further comprising:

an amplifying circuit for amplifying an electronic signal converted from the signal optical pulse,

the variable output circuit switching over, in accordance with a communication speed, a frequency band of the amplifying circuit during the period when the pulse of the second predetermined period exists.

13. The receiving circuit as set forth in claim 4, wherein:

during the period when the pulse of the second predetermined period exists, the variable output circuit switches over a response speed of the variable output circuit, in accordance with a communication speed.

14. An electronic device comprising a receiving circuit for use in an optical communication,

the receiving circuit being for outputting an output signal is outputted in accordance with a signal optical pulse incident to a light-receiving element, the receiving circuit including:

a variable output circuit for (A) detecting a pulse width of the signal optical pulse, (B) determining a pulse width of the output signal in accordance with the pulse width of the signal optical pulse, and (C) outputting the output signal.