As we dig deep into lower technology nodes in IC (integrated circuit) design, we always witness a downscale of design relative to earlier technology nodes. With each contraction in technology nodes, many things, such as the width of metal wires and transistor size, tend to be downscaled. As a result, RC (Resistive-capacitive) delays are significantly worse at 7nm technology nodes. In terms of routing resources, 7nm designs are denser than the preceding nodes. As a result, when it comes to timing in 7nm, Crosstalk in VLSI plays a crucial role.
What is Crosstalk in VLSI?
Crosstalk in VLSI is any phenomenon in electronics that occurs when a signal carried on one circuit or channel of a transmission system causes an undesirable effect in another circuit or channel. Crosstalk is typically generated by unwanted capacitive, inductive, or conductive coupling between circuits or channels. Crosstalk is a major problem in structured cabling, audio electronics, integrated circuit design, wireless communication, and other communication systems.
What’s The Mechanism Of Crosstalk In VLSI?
Every electrical signal, whether electrical, magnetic, or moving, is connected to a fluctuating field. When these fields intersect, their signals interfere with one another. Crosstalk is caused by electromagnetic interference. If two wires close to each other carry different signals, the currents in them will generate magnetic fields that will induce a lesser signal in the adjoining wire.
Electrical impedance in the return path provides shared impedance coupling between the signals in electrical circuits that share a common signal return channel, resulting in crosstalk.
Crosstalk Glitch Analysis
The charge transmitted by the switching aggressors through coupling capacitances can cause a glitch in a steady signal net. The size of the malfunction may be big enough to be seen as a different logic value by the fan-out cells of the victim net.
Crosstalk Delay Analysis
The sole distinction between crosstalk delay and crosstalk noise is that the nets are not at steady state values and some switching activities are occurring on both the victim and aggressor nets. The propagation orientation of the aggressor and victim nets influences crosstalk delay. This causes either a slower or quicker transition of victim nets.
When we operate in lower technology nodes like 7nm and below, we find a tremendous influence of crosstalk latency and crosstalk noise. In the tape-out mode, this results in serious timing and noise/glitch violations. If this crosstalk is on a clock signal, it will be even more vital to correct timing breaches promptly as modification of routing for the clock might lead to further timing violations later. As a result, all conceivable timing violation values owing to crosstalk must be determined early in the design process. We don’t have to wait for the signoff tool to report such important timing errors. Instead, we may use the timing statistics as a starting point and a goal to correct such errors early in the chip design process.
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