[IBIS-Users] AW: [IBIS] Comments on BIRD97

Hello All!

I hoped for reactions on my last email regarding BIRD97 and the u_th. Since I didn't see any responses I would like to clarify two aspects:

A) u_th
At the first glance, it seems that the u_th is a sensitive parameter, that vendors don't want to reveal.  But if you take the formula for long channel:
u_th = u_th0 + gamma*[(2*phi_F + U_SB)**0.5 - (2*phi_F)**0.5]
were u_th0, gamma, phi_F und U_SB are unknown parameters which describe the process you can see that it is not possible to derive them from the known u_th.

B) Comparison of real and calculated I_inst
concrete example: vcc=3.3V, I_pd(3.3V) = 50mA, u_th=1.5V

real I_inst(U_inst):
U_inst/V |I_inst/mA (I_real)
---------------
3.0      | 42 |
2.7      | 33 |
2.0      | 14 |
1.5      |  0 |
1.0      |  0 |

with Pc calculated I_inst(U_inst) at different U_extract:
U_inst/V    |       I_inst/mA (I_pc)
U_extract/V |3.0 |2.7 |2.0 |1.5 |1.0 |
Pc          |0.92|0.81|0.46|0.00|0.00|
--------------------------------------
3.0         | 42 | 37 | 21 |  0 |  0 |
2.7         | 38 | 33 | 19 |  0 |  0 |
2.0         | 28 | 25 | 14 |  0 |  0 |
1.5         | 21 | 19 | 11 |  0 |  0 |
1.0         | 14 | 13 |  7 |  0 |  0 |

deviation of the calculated I_inst(U_inst) to the real current:
U_inst/V    |    (1 - I_pc/I_real)*100    |
U_extract/V | 3.0 | 2.7 | 2.0 | 1.5 | 1.0 |
-------------------------------------------
3.0         |  0% | +12%| +50%|+100%|+100%|
2.7         |-15% |   0%| +42%|+100%|+100%|
2.0         |-100%|  -6%|   0%|+100%|+100%|
1.5         |  >> |  >> |  >> |   0%|   0%| 
1.0         |  >> |  >> |  >> |   0%|   0%|  >> = infinite

1) All percent-values with a negativ sign (-) represent cases were the simulation will show fewer errors than in real. ==> hidden errors
2) All percent-values with a positiv sign (+) represent cases were the simulation will show more errors than in real. ==> useless design effort
3) The table shows, that you get huge current deviations if calculated with the Power_coeff. 
4) The formula is not applicable in the region below the value of u_th (infinite or +100%).

Katja



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