| 摘要 |
PURPOSE: To adjust the tuning frequency without interference with a maximum attenuation by adopting two phase shift circuits and a noninverting circuit so as to set the gain of the entire system to be almost unity thereby making the total sum of phase differences of a feedback loop to be zero. CONSTITUTION: Since a voltage VR1 across a variable resistor 16 is in crossing with a voltage VC1 across a capacitor 14 at a right angle on a circumference of a vector, a phase difference between the input voltage E1 and the voltage NR1 changes from 90 deg. to 0 deg. according to a change in a frequency (ω) from 0 to∞. The entire phase shift quantityϕ1 of a phase shift circuit 10C is twice the phase difference and changes from 180 deg. to 0 deg. according to the frequency change. The phase of a voltage VR2 across a variable resistor 36 is deviated from the phase of a voltage VL1 across an inductor 37 by 90 deg. in a phase shift circtuit 30L similarly to above. Then a signal whose phase shift is zero is outputted at a frequency by the entire two phase shift circuits 10C, 30L. The output of the circuits 10C, 30L is fed back to an input of a noninverting circuit 50 via a feedback resistor 70 and added to a signal received via an input resistor 70. A closed loop gain is set to be nearly unity.
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