Patent ID: 7769304

Claim:
A signal light processing apparatus comprising: a light receiving unit for converting input signal light to an electric binary signal; and a level detecting unit for detecting a high level component and a low level component contained in the electric binary signal from said light receiving unit, and a peak level on a high side and a peak level on a low side of the electric binary signal containing a noise, wherein said level detecting unit comprises: a high-level signal detecting unit for detecting the high level of the binary signal modulated on the signal light; a low-level signal detecting unit for detecting the low level of the binary signal modulated on the signal light; a high-side noise peak detecting unit for detecting the peak level of the electric binary signal containing the noise in a high-level area of the binary signal modulated on the signal light; and a low-side noise peak detecting unit for detecting the peak level of the electric binary signal containing the noise in a low-level area of the binary signal modulated on the signal light, and said light receiving unit comprises: a light receiving element for converting the signal light to an electric binary signal; and an amplifying unit for amplifying the electric binary signal from said light receiving element, and outputting a non-inverted signal according to a binary signal pattern of the main signal and an inverted signal obtained by inverting the binary signal pattern as amplified electric binary signals, said level detecting unit comprises: a first half-wave rectifier circuit for half-wave-rectifying the non-inverted signal; and a second half-wave rectifier circuit for half-wave-rectifying the inverted signal; said high-level signal detecting unit detects the high level on the basis of an output from said first half-wave rectifier circuit, and said high-side noise peak detecting unit detects the peak level on the high side of the electric binary signal containing noise on the basis of the output from said first half-wave rectifier circuit; said low-level signal detecting unit detects the low level on the basis of an output from said second half-wave rectifier circuit, and said low-side noise peak detecting unit detects the peak level on the low side of the electric binary signal containing noise on the basis of the output from said second half-wave rectifier circuit.