| 摘要 |
A 90 phase shift circuit receives an input signal to generate a Q-signal and an I-signal having a phase difference of 90 therebetween. The 90 phase shift circuit has a CR-type high-pass filter having a variable capacitor and fixed resistor, a CR-type low-pass filter having a variable capacitor and a fixed resistor, and a level comparator for comparing the amplitudes of both the outputs from the filters to feed-back a control signal for controlling the cut-off frequencies of both the filters
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