A 33.6-to-46.2GHz 32nm CMOS VCO with 177.5dBc/Hz minimum noise FOM using inductor splitting for tuning extension

Abstract

Signal processing in ultra-wide bandwidths is one of the key challenges in the design of multi-Gb/s wireless transceivers at mm-Waves, where channels covering 57GHz to 66GHz are specified. Further considering spreads due to process variations and the stringent reference phase noise to ensure signal integrity calls for an ultra-wide tuning range and low-noise on-chip oscillator. Meeting this target is even more challenging when adopting an ultra-scaled CMOS technology node where key passive components suffer from a reduced quality factor (Q) [1]. In a 32nm node the thickness of metals closer to the substrate is half that in a 65nm process leading, for example, to MOM capacitors with roughly half Q. The penalty is only marginally compensated by the higher transistor f t , improved only by ~20%. Various techniques exploiting alternative tuning implementations have been published recently. Magnetic tuning methods where the equivalent tank inductance is varied through reflection of the secondary coil impedance of a transformer demonstrate outstanding tuning ranges but at the cost of a severe trade-off with tank Q and poor noise FOMs [2,3]. A bank of capacitors switched in and out in an LC tank is the most popular tuning approach [4][5][6]. However the quality factor is severely degraded, when large ranges are involved. In this work, the switched-capacitor tank of the VCO shown in Fig. 20.3.1 is centered around two different resonance frequencies by splitting the inductor through the switch M sw . In particular, an up-shift is produced when the switch is off due to its parasitic capacitance. The frequency range is significantly increased without compromising tank Q leading to large tuning range and high FOM simultaneously. Prototypes of the VCO have been realized in 32nm CMOS showing the following performances: 31.6% frequency tuning range, minimum phase noise of -118dBc/Hz at 10MHz offset from 40GHz with 9.8mW power dissipation. Despite being realized in an ultra-scaled 32nm standard digital CMOS process without RF thick metal options, the oscillator shows state-of-the-art performances.To gain insight into the advantages of the proposed technique, Fig. 20.3.2 shows a simplified equivalent circuit of an oscillator with the traditional switched-tankcapacitor C T approach and the proposed alternative consisting of a switch in series with the inductor L T . The negative resistance models the active devices while C fix , comparable or even larger than C T at mm-Waves, represents the fixed capacitance loading the tank, introduced primarily by parasitics of the negative resistance and buffer. When the switch is on, the two tanks have the same resonance frequency of 1/(2π(L T (C fix +C T )) 1/2 ).On the other hand, for the same switch parasitic capacitance c sw , the introduced technique leads to a much higher frequency jump. In fact c sw appears in series with C T +C fix instead of C T only, determining a larger variation of the equivalent tank capacitance. In the ultimate assumption of c sw <<C T , the resonance frequency o...

A 40‐GHz hybrid class‐AB/class‐BCMOSVCO with a current‐combining transformer

“…Table summarizes and compares the performance capabilities of the VCO with those of reported VCOs. The FOM T value of the VCO is –191.3 dBc/Hz, which is the highest FOM T among the CMOS VCOs …”

A Wide Tuning Range mm-Wave LC VCO

“…The stringent trade-off between quality factor and tuning range of mm-wave oscillators dictates a low tuning range for a high FOM VCO. Various techniques exploiting alternative tuning approaches have been proposed to set a compromise between tuning range and FOM [7], [8].…”

A Highly-Integrated Low-Power 10Gbps OOK Receiver for mm-Wave Short-Haul Wireless Link in CMOS 28nm

“…The mm-wave frequency range, nominally located between 30GHz and 300GHz is of great interest in this framework [2]- [3]. The spectrum is very broad and still unpopulated, allowing allocating bandwidths several GHz wide, leading to multi-Gbps communication speed even with very simple modulation techniques [4]- [6]. Moreover, with a wavelength of less than 10mm, the size of the antenna turns out to be very compact, fitting into the IC package or the chassis of small devices, allowing miniaturization with respect to current wired solutions [7].…”