| 摘要 |
PURPOSE: To obtain a signal frequency conversion circuit that can reduce leakage of an OSC signal to an output signal. CONSTITUTION: The signal frequency conversion circuit is provided with a local oscillation circuit 13, a mixer 12 that mixes a signal outputted from the local oscillation circuit 13 with an input signal to produce a frequency signal of a difference between both the signals, and a variable trap filter 37 that is inserted to an output line of the mixer 12 so as to reduce a signal level of an undesired frequency leaked to the output signal. The local oscillation circuit 13 has a PLL circuit 14, and a tank circuit 17 consisting of a variable capacitance capacitor 18 whose capacitance is controlled by an output of the PLL circuit 14 and a coil, the variable trap filter 37 consists of a coil and the variable capacitance capacitor 18, and an output of the PLL circuit 4 controls the capacitance of the variable capacitance capacitor 18. Thus, the trap filter is resonated with the same frequency as the output frequency of the local oscillation circuit 13 to trap the signal near the frequency.
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