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Chapter 3 - Analog primitives
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If the LUNIT model parameter is set to 1.0, then units for w, l, ad, as, pd and ps are (resp.)
meter, meter, meter2, meter2, meter and meter.
If the LUNIT model parameter is set to 1e-6, then units for w, l, ad, as, pd and ps are (resp.)
µmeter, µmeter, µmeter 2, µmeter 2, µmeter and µmeter.
Regardless of LUNIT, nrd and nrs are unitless and m is unitless.
Example:
.MODEL NTYP NMOS LEVEL=5 LUNIT=1 ...
* and:
M2 XOUT XIN VDD VDD NTYP W=20U L=2U AD=50P PD=150U NRD=10 NRS=20
Example:
.MODEL NTYP NMOS LEVEL=5 LUNIT=1e-6 ...
* and:
M2 XOUT XIN VDD VDD NTYP W=20 L=2 AD=50 PD=150
+ NRD=10 NRS=20
Currents in terminals
You may ask for the current in any of the four terminals of the transistor in a .TRACE or .PRINT
directive. The syntax to designate the current in terminal ‘T’ is IT(Mname).
Example:
* in circuit.pat
.TRACE TRAN ID(M42) IG(M67)
* the above directive plots the drain current of
* MOS M42 and the gate current in MOS M67.
* in circuit.nsx
M1 XOUT XIN 0 0 NTYP W=10U L=2U AD=200F PD=50P
M2 XOUT XIN VDD VDD PTYP W=20U L=2U AD=350F PD=150P NRD=10 NRS=20
Default diffusion area and perimeter
If ad, as, pd and ps are not specified and the LDIF parameter of the associated model is zero,
then the diffusion capacitances will be zero. Otherwise, the diffusion capacitances are calculated
as follows:
AS = AD = W • LDIF and PS = PD = 2 • (W + LDIF)
The value for W in the above formula is the drawn one (the one which appears in the netlist)
Parasitic resistances
nrd and nrs are used as multiplicative factors of the RSH model parameter to compute the drain
and source resistances. You should be aware that adding these series resistances, either by using
NRD/NRS in conjunction with RSH, or by using the RD/RS model parameters, will increase the
number of nodes of the circuit.
If the drain or source parasitic resistance is not zero, additional internal nodes will be created. The
source resistance creates a node named S$Mname, the drain resistance creates a node name
D$Mname.
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