Szczepkowski, Grzegorz and Farrell, Ronan
350 mV, 0.5 mW, 5 GHz, 130 nm CMOS Class-C
VCO Design Using Open Loop Analysis.
In: 23rd Irish Signals and Systems Conference, June 28-29 2012, Maynooth, Ireland.
This paper presents a design method of LC cross-coupled oscillators using a large signal
S-parameter open loop approach instead of typical negative resistance methodology presented in the liter-
ature. The open loop technique allows extraction of loaded quality factor of the complete oscillator circuit
and observe how oscillation conditions change with increasing oscillator signal amplitude. As a result,
highly non-linear modes of oscillator operation (class-C in this case), can be analysed without necessity of
conducting time consuming transient simulations. The presented method is not technology specific and
allows fast calculations under changing bias conditions. The simulated class-C 130 nm CMOS oscillator
operates at 5 GHz from a reduced power supply of 350 mV, achieving average SSB phase noise better than
-115 dBc/Hz at 1 MHz offset from the carrier, using a relatively low loaded quality factor (QL ≈ 10) LC
resonator. The presented VCO has tuning range of 280 MHz to compensate for process and temperature
variations. In steady state, MOSFET devices in the oscillator operate in class-C i.e. for VGS <Vth, resulting
in low power consumption of less than 0.5 mW RMS.
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