Simple and Accurate Approach to Implement the Complex Trans-Conductance in Time-Domain Simulators

1

• Simple and Accurate Approach to Implement the
  Complex Trans-Conductance in Time-Domain
  Simulators
• M. Homayouni, D. Schreurs, and
• B. Nauwelaers
• K.U.Leuven, Belgium

2
Outline

• Introduction to Table-Based Model
• Microwave and mm-Wave Issues
• Implementation
• Linear Model
• Non-Linear Model
• Conclusion
• Acknowledgement

3
Introduction to Table-Based Model

• Layout and equivalent circuit of CMOS FinFET
  transistor.

4
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.

5
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 (Vds0)
• Tabulated in table-files

6
Microwave and mm-Wave Issues

• Complex Trans-Conductance
• gm, represents the gain
• t, represents the channel time-delay

Complex Trans-conductance
7
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

8
Implementation

• Do microwave software support complex
  trans-conductance (time-delay)?

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
9
Implementation

• t, represents the channel time-delay
• Virtual implementation of time-delay
• Introduction of transmission line
• _at_ Gate terminal to delay the sampling voltage
• _at_ Drain terminal to delay the current of
  voltage-controlled
• current source (VCCS)

Delayed Voltage
10
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
11
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

12
Implementation

• Approximate LC-Network
• If wtltlt1 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 lt f lt 50GHz
• tlt1 psec

wt lt 0.3333 , acceptable but limited in terms of
frequency range
13
Implementation

• Comparison between model and measurement in both
  cases, with time-delay and without time-delay.
• Accuracy of model is improved due to
  implementation of time-delay.

Improvement in model accuracy
14
Implementation

• Non-linear table-based model

Integration
15
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
• Non Quasi-Static non-linear model can be
  implemented

Real trans-conductance modeled as normal
Negative capacitance
16
Conclusion

• Channel time-delay is significant at microwave
  and mm-wave 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 time-domain simulators.
• Simple method was introduced to implement non
  quasi-static non-linear table-based models.

17
Acknowledgements

• Nano-RF project IST-027150
• FinFET team at IMEC
• Andries Scholten from NXP