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Subsections
Cxxxxxxx n+ n- value
  Cxxxxxxx n+ n- expression
  Cxxxxxxx n+ n- value 
        {IC=initial-voltage}
  Cxxxxxxx n+ n- model {L=length}
        {W=width} {TEMP=temperature}
        {IC=initial-voltage}
  .CAPacitor label n+ n- expression
Capacitor, or general charge storage element.
The following probes (Transient, DC, and OP analysis) are available in
addition to those available for all basic elements.
- DT
- Time step.  The internal time step used for this
  device for numerical integration.  It is not necessarily the same as
  the global time step.
 
- TIME
- Time.  The time of the most recent calculation of
  this device.  It is not necessarily the same as the global time.
 
- TIMEOLD
- The time of the previous calculation of this
  device.  It is not necessarily the same as the global time.
 
- TIMEFuture
- The latest recommended time for the next
  sample, as determined by this device.  The actual time will probably
  be sooner than this.
 
- CHarge
- The charge stored in this capacitor.
 
- Q
- The same as Charge.
 
- Capacitance
- The effective capacitance of this device.
  For a fixed capacitor, it is constant.  It will vary if this device
  is nonlinear.
 
- DQDT
- The time derivative of charge.  Hopefully this is
  the same as current, but it is calculated a different way and can be
  used as an accuracy check.
 
- DQ
- The change in charge compared to the previous sample.
  Its primary use is in debugging models and numerical problems.
 
N+ and n- are the positive and negative element nodes,
respectively.  Value is the capacitance in Farads.
The (optional) initial condition is the initial (time = 0) value of
the capacitor voltage (in Volts).  Note that the initial conditions
(if any) apply only if the UIC option is specified on the   transient command.
You may specify the value in one of three forms:
- A simple value.  This is the capacitance in Farads.
 
- An expression, as described in the behavioral modeling chapter.
  The expression can specify the charge as a function of voltage, or
  the capacitance as a function of time.
 
- A model, which calculates the capacitance as a function of
  length and width, referencing a .model statement of type     C.  This is compatible with the Spice-3 ``semiconductor
  capacitor''.
 
A model statement may be used,, with model type C or Cap.
The parameters are:
- CJ = x
- Junction bottom capacitance. (Farads / meter
  squared).  (Default = 0.)
 
- CJSW = x
- Junction sidewall capacitance. (Farads /
  meter).  (Default = 0.)
 
- DEFW = x
- Default width. (meters).  (Default = 1e-6)
 
- NARROW = x
- Narrowing due to side etching. (meters).
  (Default = 0.)
 
- TC1 = x
- First order temperature coefficient.
  (Farads / degree C).  (Default = 0.) (Not in Spice.)
 
- TC2 = x
- Second order temperature coefficient.
  (Farads / degree C squared).  (Default = 0.) (Not in Spice.)
 
- TNOM = x
- Parameter measurement temperature.
  (degrees C.).  (Default = 27.) (Not in Spice.)
 
Capacitance is computed by the formula:
capacitance = CJ * (L - NARROW) * (W - NARROW)
  + 2 * CJSW * (L + L - 2 * NARROW)
After the nominal value is calculated, it is adjusted for temperature
by the formula:
value *= (1 + TC1 * (T-T0) + TC2 * (T-T0)^2)
 
 
 
 
 
 
 
  
 Next: Trans-capacitor
 Up: Circuit description
 Previous: Summary
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Al Davis
2001-10-28