Converter for varicaps - from 3 to 30 V

The performance of varicaps is im- proved when the voltage across them is increased. Besides better inter- modulation rejection, a 30 V circuit has a considerably higher Q than a 9 V version for the same capacitance variation. However, with battery- powered circuits, this high voltage will cause a problem, since deriving a tuning voltage of 30 V from a low supply voltage can only be realised with the aid of a converter. The circuit diagram shows the design for a converter especially constructed for this purpose. The LM 10C, from National Semiconductor, which contains two opamps and an internal reference source is ideal for this particular application. The oscillator is constructed around a 3 ... 16 V 0® converter for varicaps 82589 • 2 dual-gate MOSF ET (type BF 900) and functions at a supply voltage as low as 1.5,V. The output voltage level of the converter is controlled via the supply voltage of the oscillator. Unlike most converters, this one does not have to be switched, so...