A Compact 0.2–0.3-V Inverse-Class-F 23 Oscillator for Low 1 / f 3 Noise Over Wide

Abstract

We introduce a new mode of oscillation in an LC- tank: an inverse class-F 23. In contrast to the conventional class-F oscillators, in which a high value of the real impedance (i.e., resistance) is presented to the third (in class-F 3) or/and to the sec- ond (in class-F 2/class-F23) oscillator harmonics via an auxiliary resonance, here low resistive impedances (resembling a non-ideal short) are presented at both the second and third harmonics. This is made possible by tight magnetic coupling in the differential and common modes, respectively, afforded by a new compact 2:3 transformer. Being largely free from the harmonics in the voltage waveform and their possible deleterious phase shift effects on the flicker noise up-conversion, the phase noise performance in the flicker and thermal regions is further improved by narrowing the conduction angle. The 2:3 step-up transformer a l s op r o v i d e sah i g hp a s s i v eg a i nt oh e l pw i t ht h es t a r t u pi nf a c e of low supply. The switched-capacitor banks and cross-coupled transistor pair are carefully integrated under the transformer with a special arrangement of native (high-resistivity) substrate layer to mitigate their effect on the oscillation while reducing the area by 30%. The proposed digitally controlled oscillator (DCO) is implemented in 28-nm CMOS and achieves − 95 dBc/Hz and − 118 dBc/Hz at 100 kHz and 1 MHz offsets, respectively, while operating at a 0.3 V supply. The measured 1 / f 3 corner stays within 60 to