pingspice.analysis.mosfet.Constraints(diode.Constraints) class documentation
Part of pingspice.analysis.mosfet
(View In Hierarchy)
| Instance Variable | mp | An instance of mosfet_model.MOSFET_Physics. |
| Instance Variable | Rds_on | Minimum on-state resistance. |
| Instance Variable | Vgs_Rds_on | Vgs at Rds_on. |
| Instance Variable | VT_max | The maximum allowable value of VT. |
| Method | __init__ | Undocumented |
| Method | rds | Ensures that rd + rs is less than Rds_on, since the Ohmic extrinsic resistances don't even account for the accumulation region and fully inverted channel. |
| Method | vt | Ensures that the threshold voltage isn't too high to not allow inversion at the lowest Vgs value of setup 211. |
Inherited from Constraints:
| Instance Variable | IV_fwd_max | Maximum forward-bias current and voltage to be considered. |
| Instance Variable | R_lead | Lead resistance (each). |
| Instance Variable | Tj_min | Minimum operating temperature (deg C). |
| Method | fwd | Forward-bias voltage as determined by the diode equation must be no less than 1/2 and no more than 2x what is expected at maximum specified current. |
| Method | ts_fwd | Denominator of current source expression simulating temp-sensitive Rs must be > 0 even at coldest rated temp of Tj_min: |
Ensures that rd + rs is less than Rds_on, since the Ohmic extrinsic resistances don't even account for the accumulation region and fully inverted channel.
Also keeps rs from being larger than rd. In reality, it should be considerably smaller. Not only do electrons have to travel much farther in the drift region for rd, but the light doping there (<10% of NA in p+ region) makes its resistivity much higher than that of the p+ source region for rs. The fact that it has more cross-sectional area than the source region does not compensate much for those two factors.
Zheng Yang ("Power MOSFET," ECE442 handout) has VDMOS source plus source contact resistivity at 0.06 mOhm/cm^2, with most of that being from the contact, and drift plus substrate plus drain contact (all part of rd) being 0.41 mOhm/cm^2. (That doesn't include accumulation resistance he puts at 0.66 mOhm/cm^2 and JFET resistance at 0.19 mOhm/cm^2.) This corresponds to an rs/rd ratio of about 15%.
For UMOS, Zheng Yang has source plus contact at 0.0505 mOhm/cm^2, with the source part vanishingly small. Drift plus substrate drain contact is 0.27 mOhm/cm^2 (not including accumulation resistance he puts at 0.055 mOhm/cm^2). This corresponds to an rs/rd ratio of about 19%.