Analysis and Design of Integrated VCO in 28 nm CMOS Technology for Aerospace Applications

This paper proposes the comparison between various types of integrated VCO (Voltage Controlled Oscillator) architectures, designed in 28 nm CMOS technology, for aerospace applications. A frequency of 25 GHz and a temperature range from −40 °C to +125 °C have been taken as target, together with a low supply voltage. In particular, ring oscillators (RO) based VCOs and a LC tank VCO were designed and compared. Although RO based VCOs are attractive for the low area occupation and for the high tuning range capability, the comparison has highlighted a very high PVT (Process Voltage Temperature) sensitivity and poor phase noise performances at the target frequency for these structures. Instead, the designed LC tank oscillator has shown a lower sensitivity to PVT variations and better phase noise performances at 25 GHz, together with a lower power dissipation. A varactor-based voltage tuning control allows the LC tank VCO to recover the target frequency among PVT variations. The complete layout of this last structure has been implemented. Post layout simulations have shown a typical oscillation frequency which can be varied from 24.35 to 25.65 GHz with a phase noise of −95 dBc/Hz at 1 MHz offset from the 25 GHz carrier and a power dissipation of 860 µW. A two stage output buffer was also designed to be able to drive chip pads and test the VCO. SEEs (Single Event Effects) simulations have been performed to test circuit’s reliability in a radiation environment.