User`s guide

15
-
4 Mixed Analo
g
/Di
g
ital Simulation
In the HC/HCT series, we provide two different DtoA models:
the simple model and the elaborate model. The simple model is
accessed by specifying level 1 or 2, and the elaborate model by
specifying level 3 or 4. The HC/HCT level 1 and 2 DtoA models
provide accurate I-V curves given a fixed power supply of 5.0
volts and a temperature of 25°C. The level 3 and 4 DtoA models
model I-V curves accurately over the acceptable range of power
supply voltages (2-6 volts), and include temperature derating.
The elaborate model is noticeably slower than the simple model,
so you should only use it if you are using a power supply level
other than 5.0 volts.
Level 1 Interface
The level 1 AtoD interface generates intermediate logic levels
(R, F, X) between the voltage ranges VILMAX and VIHMIN
(specific voltages depend on the technology you are using). A
steadily rising voltage on the input of the AtoD will transition
from 0 to R at VILMAX and from R to 1 at VIHMIN. The F
level is output for steadily falling voltages in a similar manner.
The X level is produced if the input voltage starts in the
threshold region or doubles back into a previously crossed
threshold.
Level 1 (the default) is very strict in its mapping of logic levels
onto the changing input voltage. That is, the exact switching
voltage is assumed to be anywhere between VILMAX and
VIHMIN due to temperature or power supply variations. Thus,
Table 15-1
Interface Subcircuit Models
Lev
el
Subcircuits Definition
1 AtoD1/DtoA1 AtoD generates intermediate R, F, and
X levels
2 AtoD2/DtoA2 AtoD does not generate intermediate R,
F, and X levels
3 AtoD3/DtoA3 (same as level 1)
4 AtoD4/DtoA4 (same as level 2)