Hicum Model in Spectre

1
Hicum Model in Spectre

• Diana Moncoqut, RD manager
• June 4, 2004

2
CMI (Compiled Model Interface)

• A flexible and efficient low-level C-language
  interface
• A common model interface to Spectre,SpectreRF,
  AMS, UltraSim.
• Used to implement all kind of devices in the
  simulators
• Transistors Bsim3v3, Bsim4, Hicum, Mextram,
  Vbic,..
• Passive Devices Resistor, Capacitor, Inductor,
  Core, Port..
• Used by customers to introduce their proprietary
  models to Spectre.

3
Implementation in Spectre

• First implementation was done by Conexant using
  CMI in 1999
• Minor enhancements made by Cadence
• Update to version 2.1 in 2001 made by Cadence
• Enhancements suggested by ST to the substrate
  current Itss
• Itss(T) Itss(T0) (T/T0)(3/Msf)
  exp(VGB/(MsfVt) (T/T0-1)))
• Tef0 constant change from 0.01 to 1e-6
• Temperature Implementation is now complete in
  Spectre/RF

4
Hicum model advantages

• A physically based-model
• Hicum model is the only model that accurately
  describes the minority charge and transit time
• Hicum model also gives a very accurate and robust
  large signal simulation

5
Hicum model status in Spectre

• Diffusion capacitances are a simplified
  representation of the distributed minority charge
  in the transistor
• C_de/C_dc are not exact derivatives of Q_de/Q_dc
• This causes convergence problems in transient
  analysis
• Provided a work-around for this problem, and
  working on a complete solution in Q3.
• Any remaining problems in derivatives will be
  examined and fixed in Q3.

6
Hidden state problem in RF simulation

• Hidden-state problem
• A hidden state is a variable whose value is
  used before it is set, which means that its value
  is retained from a previous time point.
• In shooting-Newton, one must be able to access
  and manipulate the state of the circuit, one must
  be able to compute the sensitivity of v(t) with
  respect to v(0)
• Hidden states are a problem for any RF simulator
  based on PSS algorithms.

7
Hicum model status in Spectre

• In Hicum, Excess phase (aQf, aiT) is implemented
  using a second-order Bessel polynomial which
  introduces hidden states. For PSS to converge, we
  must  expose  the states by explicitely adding
  new signals in the system.
• Excess Phase Problems are solved in Spectre/RF by
  exposing the hidden states
• Exponential limiting. Dexp is used but EXP_MAX
  and EXP_MIN are not defined.
• Exponential limiting and PnJ limiting are added
  to Spectre/RF

8
Status of Customer Pcrs on the Hicum model
Pcr Number Title Company Release
700128 Spectre convergence with hicum model (fixed by RD) ST 5.0.33_USR3 (9/04)
706545 Spectre transient analysis problem with hicum model ST 5.0.33.500.1.14 4.4.6 ISR 138
689486 Hicum simulation results changed between IC500MSR3 IC5033 ST 5.0.33.500.1.10
604766 Hicum primitive enhancement ST 5.0.33_USR2.34.8
714103 Spectre trans. Simul. crashes with hicum in saturation mode ST 5.0.33_USR4 (11/04)
714900 Spectre hicum model wrong in DC sweep (fixed by RD) Atmel 5.0.33_ISR(17 or 18)
708954 Spectre self-heating provides a long run time simulation ST 5.0.33_USR4
708569 Spectre convergence pb. at low temp. in Hicum ST 5.0.33_USR4 (11/04)
708566 Spectre substrate current in hicum bipolar model ST 5.0.33_USR4 (11/04)