modelCj

Information

This particular model uses the space charge formula advocated in [2]. Since:

f = der(q)

the space charge, q, was symbolically differentiated. In the differentiation, only electrical signals, i.e., the voltage, e, were considered time-varying. The temperature gradients were assumed to be negligible. This produced an equation of the form:

f = C(e)*der(e)

which is the formula that was used to compute the non-linear capacitance C(e) in the model.

Notice that the junction capacitance assumes the function of the usually drawn junction diode. However in Spice, the so-called junction diode only carries the capacitive current. It computes the diodic current mathematically, but passes this information on as a modulating signal to the two non-linear current sources. Thus, the entire diodic (Ohmic) current really flows through the two non-linear current sources, which truly are non-linear resistors.

To reflect the mathematical reality of the model, a capacitor symbol was used to represent the junction capacitance in the icon layer. However, to make the circuit diagram look more familiar to Spice users, a diode was drawn as a shadow over the capacitance.

Parameters:

 Is:      Transport saturation current (default value = 1e-16 Amp)

 EG:      Energy gap for temperature effect on saturation current (default value = 1.11 Volt)

 N:       Current emission coefficient (default value = 1)

 XTI:     Saturation current temperature exponent (default value = 3)

 CJ:      Zero-bias depletion capacitance at reference temperature (default value = 0.5e-12 F)

 MJ:      Junction grading coefficient (default value = 0.333)

 VJ:      Built-in potential at reference temperature (default value = 0.75 Volt)

 XCJ:     Fraction of base-collector depletion capacitance connected to internal base node (default value = 1)

 FC:      Depletion capacitance factor for linearization (default value = 0.5)

 Tau:     Ideal transit time (default value = 1e-9 sec)

 GminDC:  Leakage conductance (default value = 1e-15 Mho)

 Area:    Relative area occupied by the diode (default value = 1)

 Level:   Transistor modeling level (Ebers-Moll = 1; Gummel-Poon = 2) (default value = 2)

 BE:      True if base-emitter junction (default value = true)

 EMin:    if x < EMin, the exp(x) function is linearized (default value = -100)

 EMax:    if x > EMax, the exp(x) function is linearized (default value = 40)

References:

1. Cellier, F.E. (1991), Continuous System Modeling, Springer-Verlag, New York, pp. 224-225.
2. Massobrio, G. and P. Antognetti (1993), Semiconductor Device Modeling with Spice, 2^nd edition, McGraw Hill, New York, p.69.

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