ECSM introduces accurate modeling capability by supporting a

1. Current Source Driver Model, characterized as a voltage versus time waveform and converted into a current source.

2. Receiver Model – a variable pin capacitance receiver model.

3. Voltage Threshold on the output.

4. Power grid waveforms for dynamic power grid analysis.

5. Power pin parasitics for dynamic power grid analysis.

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ECSM Requirements

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The ECSM extensions to Liberty are designed to meet the following requirements:

• They are compatible with existing Liberty syntax and rely on constructs such as library, global definitions, cell definition and pin definition. 

• They resemble similar Liberty constructs.

• They use the same context as the equivalent Liberty construct. For example, units are consistent. If an extension uses a voltage value and the voltage unit is defined as 1mV, the values placed in the attribute are in 1mV units.

• They should not cause any change in behavior in any non-ECSM-enabled tool that reads the Liberty format, including tools that use compiled library files.

• The extensions can be easily extracted by tools that already parse Liberty.

• Updates to existing characterization tools to create the additional data needed for ECSM should be quite minor.

 

ECSM Timing Extensions

 

The Liberty User Guide provides mechanisms for adding user-defined attributes (C.1) and groups (C.2) to the model. ECSM is defined by four elements: waveform, capacitance, threshold, and version

 

Dynamic Power Extensions

 

Dynamic current signatures of power and ground pins are represented in ECSM as current waveforms. These waveforms can be used with either two-dimensional (2D) or three-dimensional (3D) lookup tables. (The examples in this document assume a 2D lookup table, based on input slew and output loading capacitance.) These current waveforms usually have a piecewise linear (PWL) representation. 
Although waveforms of arbitrary size are allowed, it is recommended that they contain fewer than 10 points. The waveform reference time (i.e., "time zero") should be the point at which the input signal crosses its delay threshold. The first and last points on the curve need not be on the X-axis. Negative time and current values are allowed. 

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ECSM Noise Extensions

 

ECSM noise extensions requirements are:

• They must be compatible with and resemble existing ECSM constructs and Liberty™ formats.

• Updates to existing characterization tools to create the additional data needed for ECSM should be quite minor.

• They must use the same context as the equivalent Liberty™ construct. For example, units must be consistent. If an extension uses a current value and the current unit is defined as 1 milliampere, the values placed in the attribute must be in milliamperes.

• They should be easily extracted by and not cause any change in behavior in any non-ECSM enabled tool that reads the Liberty™ format including tools that use compiled library files.

 

The models required for noise analysis are similar to the models used for timing analysis, but there are some differences. Noise analysis typically consists of two different types of calculations: the effect of noise on delay, and functional or “glitch” noise.

 

Noise on delay analysis requires an accurate model of the driving stage of each gate. Glitch noise analysis requires a way to model the effective holding resistance of the output stage of the cell, while the “victim” driver is held at either a logic 0 or 1 value. Additionally, glitch noise analysis filters out small, insignificant noise according to parameters set on the inputs of the cell.

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Due to the above considerations, noise analysis tools may need detailed models for the different Channel Connected Components (CCCs) within a cell. In the context of a cell, a CCC is often referred to as a stage. Accurate modeling of cells with multiple stages requires references to gate level inputs and outputs inside the cell. In this document these inputs and outputs are referred to as internal pins.

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ECSM noise extensions introduced in this document model slew propagation, arc current, tolerance for Vdd and Vss, output pin capacitance and holding resistance. Several of the models rely upon the concept of CCCs.

 

ECSM noise extensions do not support modeling of glitch noise propagation through logic gates. Noise propagation can be supported by SPICE models on the side.

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