| 摘要 |
PURPOSE:To improves S/N by preventing the capacitor of a varicap from varying with an AC component of a hum, etc., superposed upon a control DC voltage, by applying the AC component to both terminals of the varicap in phase. CONSTITUTION:Resistance R3, grounded while connected in series to varicap D, has its value set sufficiently large and sufficiently small for the impednace of varicap D and control DC voltage V is all applied to varicap D. Further, capacitor C3 and coil L2 both have low impedance values. Thus, control DC voltage V is applied to varicap D via resistance R2 and coil L2 to vary the capacity. Since capacitor C3 and coil L2 provide low impedance and resistance R3 high impedance, an AC component of a hum superposed upon this voltage is applied across varicap D in phase, and consequently a difference in potential across varicap D disappears, so that varicap D will vary in capacity only with control DC voltage V. |
