Design of high frequency (10-30MHz) crystal oscillator

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Dr. Bognár György
Department of Electron Devices

In my essay I worked on crystal oscillator circuits which nowadays play a very important role in electronics. In my thesis I represent the theory of crystal oscillators from the simple RLC circuit to the different types of oscillator circuits. After that I demonstrate the different sequences of crystal oscillator’s analysis.

After the theoretical summary I designed a crystal oscillator circuit with the help of the Cadence design system. Firstly, I chose the suitable quartz crystal and then I measured the quartz design parameters with Vector Network Analyzer (VNA). Subsequently, I used the Collpits topology for the oscillator and I designed it in TSMC 180 nm technology. I needed to use DC current source to bias the circuit that is why I designed a constant-gm current reference. I also made some simulations, which were very helpful in understanding how the circuit works and with the results of the simulations I could parameterized the different instances of the circuit. In the next step of my work, I made a layout design for the circuit, which represents the real locations of the instances on the chip. So after this step of the design, the IC is ready to get manufactured.

In the real life the oscillation starts for the effect of electrical noise, so I analyse how the start up procedure and the start up time depends on the noise. Because of that I made different kind of noise simulations in the designed circuit. And at the end of my thesis I give different solutions to optimize and upgrade the circuit.


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