| 摘要 |
PURPOSE: A circuit for receiving signal of a remote controller is provided to cut off an external noise output of a remote controller signal receiving circuit and prevent a malfunction of a CPU and its electronic appliances by determining the whole gain of the remote controller signal receiving circuit according to an operating point gain control voltage determined depending on the size and type of an external noise and maintaining the whole gain constantly. CONSTITUTION: A pre-amplifier(110) amplifies a signal received from a photodiode equally for the whole frequency range and outputs it. An amplifying and noise canceling unit(120) receives the output signal from the pre-amplifier(110), operates a gain control voltage according to size and type of an external noise included in the gain control voltage, amplifies the output signal of the pre-amplifier(110), cancels the external noise and outputs it. A waveform detector(130) detects an original waveform from the output signal received from the amplifying and noise canceling unit(120). A waveform shaping unit(140) shapes a pulse string of the output signal detected from the waveform detector(130) and outputs it. An N type bipolar transistor(Q1) has a collector which is connected to other side of a resistance(R) which receives a power supply voltage at one side thereof and an emitter which is grounded, so as to invert the output signal of the waveform shaping unit(140) and outputs it. In the amplifying and noise canceling unit(120), a variable gain amplifier(121) variably amplifies the output signal of the pre-amplifier(110) and outputs it according to the fedback gain control voltage, a band pass filter(122) receives the output signal of the variable gain amplifier(121), limits the DC voltage level to the amplitude of 0.7V, passes only the central frequency region with the other regions removed and outputs it. A controller(123) compares an operating point reference voltage operated by using the output signal and the output voltage of the band pass filter(122) and a voltage level of the output voltage of the band pass filter(122), applies a charging current and a discharging current in a ratio of 3:1 to a capacitor, controls the gain of the variable gain amplifier(121), and operates a noise canceling reference voltage and outputs it. A comparator(124) compares the noise canceling reference voltage and the amplitude of the output signal of the band pass filter(122), and outputs the output signal of the band pass filter(122).
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