Transcript 11_Homayouni_MOS-AK_Eindhoven

Simple and Accurate Approach to Implement
the Complex Trans-Conductance in TimeDomain Simulators
M. Homayouni, D. Schreurs, and
B. Nauwelaers
K.U.Leuven, Belgium
Outline
• Introduction to Table-Based Model
• Microwave and mm-Wave Issues
• Implementation
• Linear Model
• Non-Linear Model
• Conclusion
• Acknowledgement
Introduction to Table-Based Model
• Layout and equivalent circuit of CMOS FinFET transistor.
Introduction to Table-Based Model
• Equivalent Circuit
• Intrinsic Network: Parameters that are bias-dependent, representing active
channel.
• Extrinsic Network: Parasitic elements that are bias-independent, originating
from layout pads.
Introduction to Table-Based Model
• Model (equivalent circuit parameters) is extracted from
measurements carried out on actual device.
•
•
•
•
DC-measurements
S-parameter measurements
Thermal measurements
Noise measurements
– Intrinsic Network Parameters
• Bias-dependent
• Extracted from S-parameters at hot bias condition (Vgs and Vds non-zero)
• Tabulated in table-files
– Extrinsic Network Parameters
• Bias-independent
• Extracted from S-parameters at cold bias condition (Vds=0)
• Tabulated in table-files
Microwave and mm-Wave Issues
• Complex Trans-Conductance
• gm, represents the gain
• t, represents the channel time-delay
Complex
Trans-conductance
Microwave and mm-Wave Issues
•
Influence of channel time-delay on model accuracy.
• Most sensitive parameter: S21.
Error (difference between model and measurement ) in percentage
in S-parameters due to ignorance of channel time-delay.
•
mm-Wave application:
•
•
38GHz fast Ethernet, 60GHz WLAN, 77GHz car-radar
Significant features: gain (S21), fmax, ft
Implementation
• Do microwave software support complex trans-conductance (timedelay)?
ADS (Advance Design System)
Yes
Spectre (Cadence)
No
Verilog-A
No
Spice
No
Complex trans-conductance in ADS
Gain:
gm = 45mS
time delay: t = 5.2psec
Implementation
•
t, represents the channel time-delay
• Virtual implementation of time-delay
• Introduction of transmission line
– @ Gate terminal to delay the sampling voltage
– @ Drain terminal to delay the current of voltage-controlled
current source (VCCS)
Delayed Voltage
Implementation
• How to determine and implement the t-line?
• T-line should be terminated with match-load to guarantee no
reflection.
• Input impedance of t-line should be orders of magnitudes larger than
impedance seen from connection point (Zin should be much larger
than Zout) .
• Electrical length of t-line corresponds to time-delay.
Zout
Zin
Implementation
• Implementation Issues for Simulators
• T-lines are not very convenient for time-domain simulators.
• T-lines are approximated by lumped LC-network
– Simpler to extract the values
– Simpler to develop them in model
– Limited in terms of frequency range
Implementation
• Approximate LC-Network
• If wt<<1 then the LC-network is performing as a t-line that delays the input
signal.
• t is in order of tenth of psec.
• Z0 is in order of M
• In our case (FinFET transistor):
– 300MHz < f < 50GHz
–
t<1 psec
wt < 0.3333 , acceptable but limited
in terms of frequency range
Vout
Z0
1
 jwt



1

j
wt

e
Vin
Z 0  w 2 LCZ 0  jw L (1  w 2t 2 )  jwt
Implementation
• Comparison between
model and
measurement in both
cases, with timedelay and without
time-delay.
• Accuracy of model is
improved due to
implementation of
time-delay.
Improvement in
model accuracy
Implementation
• Non-linear table-based model
Integration
Implementation
• Implementation of time-delay in non-linear model
• Different from linear model
• No need for t-line or equivalent lumped network
• Complex trans-conductance can be split into real and imaginary parts
gm e jwt  gm cos(wt )  jgm sin(wt )
if wt < 1
gm e jwt
gm  jw ( gmt )  gm  jw ( gmt )
Real trans-conductance:
modeled as normal
Negative capacitance
• Non Quasi-Static non-linear model can be implemented
Conclusion
• Channel time-delay is significant at microwave and mmwave frequencies.
• Accurate technique was introduced to introduce complex
trans-conductance in time-domain simulators.
• Simple and accurate approximation was introduced to
ease the time-delay implementation in model for timedomain simulators.
• Simple method was introduced to implement non quasistatic non-linear table-based models.
Acknowledgements
• Nano-RF project IST-027150
• FinFET team at IMEC
• Andries Scholten from NXP