No-bias L-C High-Frequency Oscillator


Posted on Feb 7, 2014

This oscillator requires no biasing components. Only an inductor and various matching or tuning capacitors are required to set the operating frequency. The active element is the 74HCU04 hex inverter. Only one of the six inverters is required for the oscillator another may be used as a buffer. A few oscillator circuits are presented, including


No-bias L-C High-Frequency Oscillator
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design procedures. Most HCMOS gates are buffered . In the case of buffered inverters like the 74HC04, a single inverter is constructed from three cascaded inverters. The HCU04 is much simpler with each inverter composed of one enhancement NMOSfet and one PMOSfet in totem-pole configuration. The NMOSfet`s gate and PMOSfet`s gate are tied together at the input pin, and their drains are tied together at the output pin. When biased mid-way between supply (Vcc) and ground, this structure is a reasonably linear amplifier. Open-loop gain is measured at 12. 5, with transconductance 0. 023 amps/volt. Output impedance measures 557 ohms. All are dependent on supply voltage (from a Philips data sheet): Since an oscillator`s input or output voltage will be swinging over a considerable range of the 5v supply voltage, the non-linear characteristics of the amplifying inverter have significant influence over the AC operating amplitude. Swings above Vcc or below ground are clamped by internal diodes and can cause latch-up of the device. Operation too close to the rails should be avoided. The onset of non-linearity such as reduced transconductance or reduced output impedance serve as the mechanism by which amplitude is stabilized every oscillator employs similar means of amplitude control. Of the basic oscillator types, the non-inverting types such as Hartley or Colpitts are not achievable with a single HCU04 amplifier. Pierce and Vackar are...




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