Why study SOI MOSFETs nonlinearities ?. MOSFET SOI. f. f. Simplified process Low parasitic capacitances Low leakage current Low Vth => promising for RF ICs. Distortion . Silicon-on-Insulator (SOI). Non-idealities of “linear circuits” Amplifiers Active filters
Impact Ionization current
High E field near the drain:
=> impact ionization => creates e--h+pairs
=> injection of holes inside the body
=> body potential increase up to Vtsb
=> Parallel path for Id and Id increase
=> Vt lowering and Id increaseWhat happens inside?- gd kink -
=> Does the kink influence the linearity ?
=> Which methods to characterize the linearity of MOSFETs ??
The simplest is the best
If the circuit is excited by a sine wave,
Consider the memoryless nonlinear system:
2. Observe that Area1-Area2 is
proportionnal to the THD
3. Define theD function
1. Normalize the characteristics
HD3is obtained by computing the D function of Ir = I(V)-I(-V)
=> even harmonics eliminated
! HD of order higher than 3 are neglected
Not by a scale factor as from Taylor approach, cfr.
full-wave (magnitude and phase) RF (900 MHz) characterization
(V,I fundamental and harmonics at input and output) in single take
=> Real RF nonlinear behavior
900 MHz, 50 Ω, A = 0.2 V
Gm Gd Cds
=> Answer this question with the help of a Volterra series based model:
DC method vs 900 MHz measurements in agreements
=> Which frequency limit ??
Pole Voltage Gain Av
PD, from ST Microelectronics
60x 1µm/0.12 µm, f=2 GHz
FB: higher fT, fmax than BC and isoc.
BC/Isoc.: parasitic C, gm degradation