| 摘要 |
PROBLEM TO BE SOLVED: To provide a tuner for receiving satellite broadcast that can enhance its reception performance by obtaining linearity in a signal attenuation characteristics in an AGC circuit against a wide range of input signal levels. SOLUTION: The AGC circuit of the tuner for receiving satellite broadcast is provided with an optical coupling circuit A having a light emitting element (23) introducing an optical output in response to a control signal from an AGC control circuit (13) and a light receiving element (24) receiving light outputted from the light emitting element and reflected by an optical reflecting plate (26), and an AGC control signal in response to the control signal is derived from the output side of the coupling circuit A and the AGC control signal controls the signal attenuation of an RF.AGC circuit section (3). In this case, the slope of the signal attenuation in the RF.AGC circuit section (3) is properly set by adjusting the optical coupling degree of the optical coupling circuit A to obtain the linearity of the signal attenuation characteristics.
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