Efficient mm-Wave and THz Circuits and Systems
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Millimeter-wave and Terahertz circuits are gaining more attraction in communication and sensing applications. This is mainly due to the advancement in IC fabrication technology which allows for higher values for fmax and thus higher operating frequencies. Nevertheless, operating near that limit is very challenging because of the low activity of the transistors and high losses in passives due to skin effect. This will require the use of larger transistors and more power consumption. Unfortunately, increasing the size of the transistor will limit the operating frequency. Harmonics generated from the non-linearity will leak part of the energy if not used. This is applicable to oscillators and amplifier as well. Multistages are needed due to the low gain in amplifiers which when properly conditioned for high activity, act as resonators limiting the bandwidth. This work address these limitations by applying several techniques to oscillators and amplifiers.
The first technique uses super-harmonic self-injection locking in oscillators to utilize the unused harmonics enhancing the performance at the fundamental frequency. More than 10dB improvement in phase noise was measured for an oscillator with fundamental frequency extraction at 105GHz and another with harmonic extraction at 210GHz. An application out of this dynamics between the oscillator and its harmonics is IQ generation. Two IQ oscillators have been designed, one at 105GHz and another at 220GHz where the 2nd harmonic is above fmax of the technology. The second technique uses the properties of periodic structures to allow for multiple cascading of amplifiers with no limit on the number of stages and thus enable the use of minimum size transistors. The circuit can amplify up to the unity-current gain frequency fT. The amplifier designed has the highest gain at 260GHz and it has been constructed using 200 transistors.
Chair: Professor Ehsan Afshari