BIAS/ERASE OSCILLATOR

摘要

An oscillator circuit is provided for obtaining a low distortion signal for bias and erase. The circuit is made up primarily of two sections. One of the sections is a frequency determining LC tank. Low distortion oscillation is produced with a low Q tank, and supply current is low relative to the tank current. The other is an AC coupled negative resistance element having a capacitive voltage divider. The LC tank is made up of a first inductor, and a second inductor which is the erase winding. The tank also has a series combination of first and second capacitors. The negative resistance element is formed by a differential pair of first and second transistors. This pair of transistors is DC biased to a reference voltage through a first resistor, with a capacitor providing decoupling. A second resistor provides a load for the reference voltage. The base of the second transistor is biased by a third resistor. The DC current through the first and second transistors is adjusted by a fourth resistor, while fifth and sixth resistors make the current through the fourth resistor split nearly evenly through the transistors.