eldo_user

Specifying Simulation Output
High Impedance Node Checks
High Impedance Node Checks
A high impedance node (Hi-Z) refers to a circuit node in high impedance state. Eldo detects
circuit Hi-Z states by checking the dynamic behavior of all nodes. This detection method works
on any circuit topology and applies to all device types.
Tip
You can view high impedance detections with the AMS Results Browser.
How to Enable High Impedance Node Checks
To enable high impedance node checks use one of the commands: .DCHIZ, .HIZ,
.OPTION ADIT_CHECK.
Hi-Z detection is controlled by two parameters: GFLOAT_MAX and HIZ_TIME.
The Hi-Z detection algorithm evaluates nodes’ conductance as well as voltage and current
convergence criteria. This method allows more accurate and comprehensive Hi-Z detection
compared to just evaluating conductance or voltage. Instead of having to control three
parameters, namely voltage, current and conductance, a pseudo-conductance value
(GFLOAT_MAX) is provided as the controlling parameter for the algorithm. The guideline is
to set GFLOAT_MAX close to the conductance at Hi-Z; it does not set the exact conductance
limit in which nodes are reported as Hi-Z. You can use GFLOAT_MAX to increase or decrease
the number of nodes reported as Hi-Z. The default value is 1e-7. The smaller the
GFLOAT_MAX value, the less number of nodes to be reported as Hi-Z.
HIZ_TIME can be used to report only nodes that stay in Hi-Z state for longer than a specified
time. The default value is 0, which means a node in Hi-Z state is reported as soon as it is
detected at each transient time point. Reporting instantaneous Hi-Z states can generate massive
reports and raise false alarm. It is recommended to define HIZ_TIME appropriately to only
highlight significant Hi-Z states.
In the circuit check report, Hi-Z nodes are categorized into two groups:
• [HiZ_NULL_FANOUT] means the Hi-Z node does not drive any devices (has no
fanout).
• [HiZ] means the Hi-Z node drives some devices.
Example Hi-Z check report from .OPTION ADIT_CHECK:
[HiZ]:node(x1.n0) Hi-Z status from 1.58204e-05 to 5e-05
[HiZ_NULL_FANOUT]:node(x1.nms) Hi-Z status from 0 to 5e-05
[HiZ_NULL_FANOUT]:node(x1.nps) Hi-Z status from 0 to 5e-05
Example Hi-Z check report from .HIZ command:
Eldo® User's Manual, 15.3 349