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Silicon versus Gallium-Arsenide Varactors

May 2nd Fact-of-the-Day

Varactors are solid-state voltage-variable capacitors that can be made of silicon or gallium-arsenide. Silicon varactors generally are less expensive than gallium arsenide varactors. Gallium arsenide varactors have high Q's (lower losses) and can be used at higher frequencies. However, their higher Q's do not automatically guarantee better performance. For example, silicon varactors typically generate less FM noise when used in voltage controlled oscillators than gallium-arsenide varactors do. The higher gallium-arsenide FM noise is due to up-conversion of surface noise. Thermal-oxide-passivation silicon varactors can be used to reduce FM noise in voltage controlled oscillators, but there is no known passivation for gallium arsenide that will limit surface-state noise. ©2005 Martek International All rights reserved.

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