Study And Design Of Radiation Hardened Digital Circuits In Fractional Synthesizer

With information technology developing, device working under radiation environment becomes a hotspot. As the key device of wireless communication system in the space, research on rad-hardened frequency synthesizer means a lot. This paper mainly designs fractional divider and relative digital circuits, including ∑-A modulator、 programmable multi-modulus divider、 power on reset(POR) and SPI. To improve radiation tolerance, applying bilateral resetting、bit-line segregation and tri-mode redundancy technologies, this paper proposes bilateral resetting POR and dual interlocked storage cell(DICE) flip-flop. This paper employs ∑-Δ modulator and adds Dither and Notch module to minish spurs, then models and simulates on behavior level with Matlab-Simulink.2/3 prescaler with SCL structure, programmable counter and swallow counter are applied to design programmable multi-modulus divider. To harden the radiation tolerance further, ∑-Δ modulator、programmable counter, swallow counter and SPI all employ rad-hardened DICE flip-flop. With TSMC 0.18μm process, schematics and layouts as well as simulations are designed. POR、DICE flip-flop and programmable multi-modulus divider are implemented with Cadence Virtuoso platform, while ∑-Δ modulator and SPI are implemented with synthesis automatic place and route flow. The results of basic electrical test show that while the reference frequency is 40MHz, fractional divider based on ∑-Δ modulator can do 30-60 divide normally from 1.2GHz to 2.4GHz as well as suppress the fractional spurs and POR and SPI works well. The results of single event test show that when LET reaches 37.2 MeV·cm2·mg-1, the chip works correctly, the radiation tolerance is good which satisfies the system requirement. Consequently, circuits designed in this paper can be applied for the chips in the field of aerospace.