| 摘要 |
PROBLEM TO BE SOLVED: To provide a filter circuit having a piezoelectric resonator that has a high square shape in an output signal. SOLUTION: A 1st differential circuit 3 consists of transistors(TRs) Q1, Q2 whose emitters are respectively connected to current sources S1, S2, and a crystal filter CF is connected between the emitters of the TRs Q1, Q2. A 2nd differential circuit 4 consists of TRs Q3, Q4 whose emitters are respectively connected to current sources S3, S4, and a compensation circuit 5 is connected between emitters of the TRs Q3, Q4. An output circuit 6a consists of a parallel circuit consisting of a resistor R! and a capacitor C2 connected to an output terminal 2a and a parallel circuit consisting of a resistor R2 and a capacitor C3 connected to an output terminal 2. An output of the 1st differential circuit 3 to which the crystal filter CF is connected and an output of the 2nd differential circuit to which the compensation circuit 5 is connected are put together in phase and the output circuit 6a filters the resultant output to obtain an output signal.
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