Analysis and Design of a 195.6 dBc/Hz Peak FoM P-N Class-B Oscillator With Transformer-Based Tail Filtering

Abstract

A complementary p-n class-B oscillator with two magnetically coupled second harmonic tail resonators is presented and compared to an N-only reference one. An in depth analysis of phase noise, based on direct derivation of the Impulse Sensitivity Function (ISF), provides design insights on the optimization of the tail resonators. In principle the complementary p-n oscillator has the same optimum Figure of Merit (FoM) of the N-only at half the voltage swing. At a supply voltage of 1.5 V, the maximum allowed oscillation amplitude of the N-only is constrained, by reliability considerations, to be smaller than the value that corresponds to the optimum FoM even when 1.8 V thick oxide transistors are used. For an oscillation amplitude that ensures reliable operation and the same tank, the p-n oscillator achieves a FoM 2 to 3 dB better than the N, only depending on the safety margin taken in the design. After frequency division by 2, the p-n oscillator has a measured phase noise that ranges from 150.8 to 151.5 dBc/Hz at 10 MHz offset from the carrier when the frequency of oscillation is varied from 7.35 to 8.4 GHz. With a power consumption of 6.3 mW, a peak FoM of 195.6 dBc/Hz is achieved.

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“…Consequently, each of them has its own set of advantages and drawbacks such that their minimum achievable P DC and FoM are almost identical, as shown in Table II. Note that applying a tail filtering technique to a class-B oscillator increases its α V [22], [33], which is in line with the FoM optimization but against the P DC reduction, as evident from (1) and (4). Furthermore, while maintaining the same R in , a class-F 3 operation does not reduce P DC of traditional oscillators, since its minimum V DD , α V and α I are identical to OSC N [24].…”

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