| 摘要 |
PURPOSE:To improve the linearity of frequency shift by using a piezoelectric body having prescribed cross finger type electrodes to constitute the acoustic delay line of an oscillating circuit where the output is positively fed back to an amplifier after being delayed by a phase shifting circuit and the delay line. CONSTITUTION:A frequency modulator consists of an amplifier 1, a phase shifting circuit 2, and an acoustic delay line 3. A modulation signal 104 is inputted from a terminal 4 and a modulated high-frequency signal 102 is outputted from a terminal 5. A high-frequency signal 101 of the output of the amplifier 1 has the phase delayed by the phase shifting circuit 2 and is delayed by the delay line 3 with respect to time and is fed back to the amplifier 1. Cross finger type electrodes 31 and 32 are provided on the surface of a piezoelectric ceramic thin plate 300 to constitute the delay line 3, and this constitution satisfies D<1.2/F and P=V/F where D is the thickness of the thin plate 30 and P is the arrangement period of fingers of cross finger type electrodes and V is the velocity of the SH wave excited in the thin plate 30 and F is the carrier frequency.
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