Standard CMOS nonvolatile reprogrammable switch for low-phase noise in LC oscillators

A nonvolatile reprogrammable switch is characterized in a standard CMOS process. LC oscillators operating between 1–2GHz utilize the switch to minimize phase noise deviation over tuning range. Bond wires are configured as high-quality inductors to achieve low phase noise; tapping that inductance enhances performance.; Further phase noise improvements target the varactor. Diodes, the most common varactor, cause a small deviation in phase noise versus tuning range. Given the small deviation, phase noise is reported as a single value. With the growing popularity of MOS technologies, other varactors become available. An accumulation-mode MOS capacitor exhibits a phase noise deviation similar to the diode varactor. An inversion-mode MOS capacitor demonstrates large tuning range but sacrifices phase noise performance in the middle of the tuning range.; Previous LC oscillator designs with inversion-mode MOS varactors measure phase noise at the limit of the tuning range where performance is best, and that single value is reported in accordance with industry practice. This work investigates phase noise performance over the entire tuning range where measured phase noise deviation exceeds 40dB for a 1.25pF inversion-mode MOS varactor. Instead of a large single varactor, a smaller varactor is utilized with switchable fixed capacitance. While an equal tuning range is achieved, the phase noise deviation is reduced by 30dB.; To obtain a switchable fixed capacitance, a new switch is developed. Without the advantage of extra process layers, hot electron programming writes the device in two minutes, ultraviolet exposure erases in twenty minutes, and a 5nm oxide retains 95% of its charge for fifty years. When included in an LC oscillator, this switch enables a 42% tuning range at a center frequency of 1.585GHz using 23.4mW of power in a 0.25μm process. The measured phase noise at 100kHz offset is −90dBc/Hz and the phase noise deviation is less than 10dB.; The nonvolatile reprogrammable switch also circumvents limitations associated with use of bond-wire inductances. Variations in excess of 40% can be recalibrated post-packaging, ensuring that bond-wires can now be used repeatably, reliably, and cost-effectively as inductors in standard CMOS processes.