| 摘要 |
PURPOSE:To obtain the output signal high in S/N with a simple circuit, by driving the photo electric conversion means APD with the signal generator in the same frequency as carrier frequency, in photo reception of optical analog AM communication system. CONSTITUTION:The APD4 is driven at the signal generator 11 producing the same frequency as the carrier-frequency f1 of incident light emitted from the light path 1, or producing the frequency f2 apart from it by f0. Since APD4 has the amplification depending on the applied voltage, the input signal is in AM demodulation and the original base band signal or the intermediate frequency signal in frequency f0 can be picked up. Since the photo detection output current is converted from high frequency f1 to lower frequency f0, the noise level at high gain amplifier 12 is low to obtain the output signal of high S/N easily. Accordingly, high frequency amplifiers which have been required in conventional systems is not necessary to simplify the circuit constitution. |
