Passive Techniques to Reduce Supply Sensitivity in an LC Oscillator Achieving 46-dB Suppression
Renxu Yang (HKUST(GZ))
R. B. Staszewski (University College Dublin)
M. Babaie (TU Delft - Electrical Engineering, Mathematics and Computer Science, TU Delft - QCD/Babaie Lab)
Z. Zong (TU Delft - Electrical Engineering, Mathematics and Computer Science)
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Abstract
This paper proposes two fully passive techniques to reduce the supply sensitivity of an LC oscillator. An RC low-pass filter is employed to reduce the supply sensitivity of coarse-tuning switched capacitors stemming from code-dependent parasitic capacitance. To cancel the remaining supply sensitivity, the supply variations are scaled and coupled to polarity-switchable varactor pairs, which are introduced in the resonator to provide a frequency tuning gain that is reverse to the supply sensitivity. A programmable capacitive divider is used to scale the supply variations by a proper ratio. The proposed techniques are applied in a 5.83-6.99 GHz class-B LC oscillator. Prototyped in 65-nm CMOS, the oscillator occupies 0.24 mm
2 and consumes 6.8 mW from 1 V. With supply perturbations in the 0.1-50 MHz frequency range, the measured reduction of the supply sensitivity is 20-46.2 dB, which is the highest reported over a wide frequency range. Benefiting from the fully passive implementation, the proposed techniques do not consume extra power or degrade the phase noise.