Oscillators - Oscillators EERF6395 RF/Microwave Systems...

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Oscillators EERF6395 RF/Microwave Systems Engineering Dr. R. E. Lehmann
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Oscillators Oscillators convert DC power into AC signals 1-port device They are non-linear circuits that rely on feedback to ensure continuous oscillation. Oscillators must be “unstable” to operate Semiconductors make use of their negative resistance to achieve oscillation
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Magnetron (Cavity) Oscillator Magnetron Oscillator A cavity magnetron is a high-power tube that produces microwaves for applications such as microwave ovens. Ref: http://en.wikipedia.org/wiki/Magnetron
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Types of Oscillators Crystal Oscillator Use of fundamental resonant properties of crystals to achieve high quality, low frequency oscillators Transistor Oscillator Free-running (FET, BJT) VCO = Varactor-controlled Oscillator DRO = Dielectric Resonator Oscillator YIG-tuned Oscillator Cavity Oscillator (Highest Q) Frequency Synthesizer Fundamental frequency is multiplied up to desired frequency Stable Local Oscillator (STALO) DDS = Direct Digital Synthesis
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Crystal Oscillators Mechanical resonance of a vibrating quartz crystal Piezoelectric effect Can be modeled with RLC ckt Very stable over temperature Frequencies: KHz – MHz Commonly used for watches and digital ICs 4 MHz Quartz Crystal enclosed in a HC/49US package used in a Crystal Oscillator Ref: http://en.wikipedia.org/wiki/Crystal_oscillator Equivalent Circuit
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Radio Architecture (Pt-Pt., LMDS, SatCom) RX TX LO IF IF Mixer Mixer LNA DA PA Multiplier PA
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Transmitter – Frequency Source IF Mixer DA PA Frequency Source LO X N Multiplier IF Amp
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