Reducing phase noise degradation due to vibration of crystal oscillators

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Nelson, Cory
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Mani Mina
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Electrical and Computer Engineering

The Department of Electrical and Computer Engineering (ECpE) contains two focuses. The focus on Electrical Engineering teaches students in the fields of control systems, electromagnetics and non-destructive evaluation, microelectronics, electric power & energy systems, and the like. The Computer Engineering focus teaches in the fields of software systems, embedded systems, networking, information security, computer architecture, etc.

The Department of Electrical Engineering was formed in 1909 from the division of the Department of Physics and Electrical Engineering. In 1985 its name changed to Department of Electrical Engineering and Computer Engineering. In 1995 it became the Department of Electrical and Computer Engineering.

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  • Department of Electrical Engineering (1909-1985)
  • Department of Electrical Engineering and Computer Engineering (1985-1995)

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In the radio communications industry, one major problem is the vibration induced on to a frequency standard. The most commonly used frequency standard is the crystal oscillator; as the crystal oscillator gets vibrated with varying force and frequencies of vibration the phase noise of the signal changes. As the phase noise increases, the signal to noise ratio decreases causing the likelihood of transmitting or receiving an incorrect signal to rise. This makes it critical to limit the phase noise increase that occurs in the frequency standard of the system.

Mechanical isolation systems have been implemented in the industry to limit the system vibration that propagates to the frequency standard. These systems add weight and size to the overall design, which make them not ideal for all applications. For systems that can not use isolators, open loop cancellation has been implemented in past designs. This cancellation measures the vibration and subtracts it from the phase noise, but such a system has drawbacks with changes in vibration frequency and force. A closed loop design is suggested to correct this.

In order to maximize performance an IQ modulation feedback system was designed. The feedback system utilizes information about both the vibration and the measured phase noise. It uses these two inputs concurrently to correct the output frequency of the crystal as it changes with vibration. In order to reduce the space and weight of the design, mechanical vibration dampeners were removed.

After various tests and simulations it was determined that using this feedback to the oscillator could correct the oscillator's frequency change based on the vibration experienced. This would reduce the phase noise of the oscillator compared to an oscillator vibrated without any compensation. Using this compensation system would reduce the overall phase noise of any communication system currently in use that utilizes crystal oscillators

Fri Jan 01 00:00:00 UTC 2010