In an
integrated circuit
An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...
, a signal can couple from one node to another via the substrate. This phenomenon is referred to as substrate coupling or substrate noise coupling.
The push for reduced cost, more compact circuit boards, and added customer features has provided
incentives for the inclusion of
analog
Analog or analogue may refer to:
Computing and electronics
* Analog signal, in which information is encoded in a continuous variable
** Analog device, an apparatus that operates on analog signals
*** Analog electronics, circuits which use analog ...
functions on primarily digital MOS
integrated circuit
An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...
s (ICs) forming
mixed-signal ICs. In these systems, the speed of digital circuits is constantly increasing, chips are
becoming more densely packed, interconnect layers are added, and analog resolution is increased. In addition, recent increase in wireless applications and its growing market are introducing a new set of aggressive design goals for realizing mixed-signal systems.
Here, the designer integrates
radio frequency
Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the upp ...
(RF) analog and base band digital circuitry on a single chip.
The goal is to make single-chip radio frequency
integrated circuits (RFICs) on silicon, where all the blocks are fabricated on the same chip.
One of the advantages of this integration is low power dissipation for portability due to a reduction in the number of package pins and associated bond wire capacitance.
Another reason that an integrated solution offers lower power consumption is that routing high-frequency signals off-chip often requires a 50Ω
impedance match
In electronics, impedance matching is the practice of designing or adjusting the input impedance or output impedance of an electrical device for a desired value. Often, the desired value is selected to maximize power transfer or minimize sign ...
, which can result in higher power dissipation.
Other advantages include improved high-frequency performance due to reduced package interconnect parasitics, higher system reliability, smaller package count, and higher integration of RF components with VLSI-compatible digital circuits.
In fact, the single-chip transceiver is now a reality.
The design of such systems, however, is a
complicated task. There are two main challenges in realizing
mixed-signal ICs. The first challenging task, specific to RFICs, is to fabricate good on-chip passive elements
such as high-Q
inductor
An inductor, also called a coil, choke, or reactor, is a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it. An inductor typically consists of an insulated wire wound into a c ...
s. The second challenging task, applicable to any mixed-signal IC and the subject
of this chapter, is to minimize noise coupling between various parts of the system to avoid any malfunctioning
of the system.
In other words, for successful system-on-chip integration of mixed-signal systems, the
noise coupling caused by nonideal isolation must be minimized so that sensitive analog
circuits and noisy digital circuits can effectively coexist, and the system operates correctly.
To elaborate, note that in mixed-signal
circuits, both sensitive analog circuits and high-swing high-frequency noise injector digital circuits may be
present on the same chip, leading to undesired signal coupling between these two types of circuit via the conductive substrate.
The reduced distance between these circuits, which is the result of constant technology scaling (see
Moore's law
Moore's law is the observation that the number of transistors in a dense integrated circuit (IC) doubles about every two years. Moore's law is an observation and projection of a historical trend. Rather than a law of physics, it is an empir ...
and the
International Technology Roadmap for Semiconductors
The International Technology Roadmap for Semiconductors (ITRS) is a set of documents produced by a group of semiconductor industry experts. These experts are representative of the sponsoring organisations which include the Semiconductor Industry A ...
),
exacerbates the coupling.
The problem is severe, since signals of different nature and strength interfere,
thus affecting the overall performance, which demands higher clock rates and greater analog
precisions.
The primary mixed-signal noise coupling problem comes from fast-changing digital signals
coupling to sensitive analog nodes.
Another significant cause of undesired signal
coupling is the
crosstalk
In electronics, crosstalk is any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel. Crosstalk is usually caused by undesired capacitive, induc ...
between analog nodes themselves owing to
high-frequency/high-power analog
signals.
One of the media through which mixed-signal noise coupling occurs is the substrate.
Digital operations cause fluctuations in the underlying substrate voltage, which spreads
through the common substrate causing variations in the substrate potential of sensitive
devices in the analog section.
Similarly, in the case of crosstalk between analog nodes, a signal can couple from one
node to another via the substrate.
This phenomenon is referred to as ''substrate coupling'' or ''substrate noise coupling''.
Modelling, analysis, and verification of mixed signal coupling
There is a sizeable literature on substrate, and mixed signal coupling. Some of the most common topics are:
*Differentiating between the random noise inherent to electronic devices and the deterministic noise generated by circuits.
*Examining the physical phenomena responsible for the creation of undesired signals in a digital circuit and the mechanisms of their transport to other parts of the system. The substrate is the most common coupling mechanism, but capacitive coupling, mutual inductance, and coupling through power supplies are also analyzed.
*Comparing various modeling approaches and simulation techniques. There are many possible models for digital noise generation, the substrate impedance network, and the sensitivity of the (unintended) receiver. The chosen techniques significantly influence the speed and accuracy of the analysis.
*Substrate and mixed-signal analysis techniques can be applied to
placement and power distribution synthesis.
References
*''Electronic Design Automation For Integrated Circuits Handbook'', by Lavagno, Martin, and Scheffer, {{ISBN, 0-8493-3096-3 A survey of the field of
electronic design automation
Electronic design automation (EDA), also referred to as electronic computer-aided design (ECAD), is a category of software tools for designing Electronics, electronic systems such as integrated circuits and printed circuit boards. The tools wo ...
. This article was derived, with permission, from Chapter 23 of Book 2, ''Mixed-Signal Noise Coupling in System-on-Chip Design: Modeling, Analysis, and Validation'', by Nishath Verghese and Makoto Nagata
Further reading / External links
Technical Book: "Noise Coupling in Integrated Circuits: A Practical Approach to Analysis, Modeling, and Suppression", by Cosmin Iorga, Ph.D., 286pages, Hardcover
Electronic design
Electronic design automation
Electronic engineering
Integrated circuits