This document discusses the fabrication of passive devices in integrated circuits, including inductors, transformers, and varactors. It notes the need for on-chip inductors and transformers to avoid issues with off-chip components. Common structures for on-chip inductors include spiral geometries, which can be circular, octagonal, or stacked. Methods to reduce parasitic capacitances in inductors include using ground shields or increasing line spacing. Transformers are typically built from coupled spiral inductors and can be planar or stacked. Varactors are voltage-dependent capacitors important for oscillator design with a critical capacitance range.
SPICE LEVEL I/LEVEL II/LEVEL III AND BSIM MODELSPraveen Kumar
SPICE LEVEL I/LEVEL II/LEVEL III AND BSIM MODELS
SPICE introduction
working
adaptions
detailed discussion on each models
SPICE Modeling in BSIM
features
bulk voltage on large signal model
velocity saturation
weak inversion operation
impact ionization
SPICE LEVEL I/LEVEL II/LEVEL III AND BSIM MODELSPraveen Kumar
SPICE LEVEL I/LEVEL II/LEVEL III AND BSIM MODELS
SPICE introduction
working
adaptions
detailed discussion on each models
SPICE Modeling in BSIM
features
bulk voltage on large signal model
velocity saturation
weak inversion operation
impact ionization
SHORT-CHANNEL EFFECTS
A MOSFET is considered to be short when the channel length ‘L’ is the same order of magnitude as the depletion-layer widths (xdD, xdS). The potential distribution in the channel now depends upon both, transverse field Ex, due to gate bias and also on the longitudinal field Ey, due to drain bias When the Gate channel length <<1 m, short channel effect becomes important .
This leads to many
undesirable effects in MOSFET.
The short-channel effects are attributed to two physical phenomena:
A) The limitation imposed on electron drift characteristics in the channel,
B) The modification of the threshold voltage due to the shortening channel length.
In particular five different short-channel effects can be distinguished:
1. Drain-induced barrier lowering and “Punch through”
2. Surface scattering
3. Velocity saturation
4. Impact ionization
5. Hot electrons
IR Drop Analysis and Its Reduction Techniques in Deep Submicron TechnologyIJERA Editor
This paper presents a detailed conceptual analysis of IR Drop effect in deep submicron technologies and its reduction techniques. The IR Drop effect in power/ground network increases rapidly with technology scaling. This affects the timing of the design and hence the desired speed. It is shown that in present day designs, using well known reduction techniques such as wire sizing and decoupling capacitor insertion, may not be sufficient to limit the voltage fluctuations and hence, two more important methods such as selective glitch reduction technique and IR Drop reduction through combinational circuit partitioning are discussed and the issues related to all the techniques are revised.
Power gating is the main power reduction techniques for the static power. As long as technology scaling is taking place, static power becomes paramount important factor to the VLSI designs.Therefore Power gating is the recent power reduction technique that is actively in research areas.
Nanometer layout handbook at high speed designMinho Park
I made this contents for whom is about to layout own's IC design. I think it would be helpful to consider layouts about high speed Rx / Tx.
Specially it was aimed giga hertz bandwidth I/O with its ESD protection (I am still working on that items to rearrange with my knowledge to my experiences)
I showed up all references and all images (except originals) are belong to own's copy rights.
Hi, im Perlis polytechnic student, and now i undergo last semester already. And i taken one interesting subject is CMOS IC design. So this is one of lab work that i uploading. Using L-Edit to design NAND gate.
This ppt is about full adder design using pass transistor logic. This circuit describe power reduction using proposed cell as standard element in technology library design for ultra low power. we provide guidance to m.tech students in thier final year research projects. We assist on IEEE projects to M.tech or PhD students. Students can contact us for VLSI Projects, Antenna Projects, MATLAB Projects
SHORT-CHANNEL EFFECTS
A MOSFET is considered to be short when the channel length ‘L’ is the same order of magnitude as the depletion-layer widths (xdD, xdS). The potential distribution in the channel now depends upon both, transverse field Ex, due to gate bias and also on the longitudinal field Ey, due to drain bias When the Gate channel length <<1 m, short channel effect becomes important .
This leads to many
undesirable effects in MOSFET.
The short-channel effects are attributed to two physical phenomena:
A) The limitation imposed on electron drift characteristics in the channel,
B) The modification of the threshold voltage due to the shortening channel length.
In particular five different short-channel effects can be distinguished:
1. Drain-induced barrier lowering and “Punch through”
2. Surface scattering
3. Velocity saturation
4. Impact ionization
5. Hot electrons
IR Drop Analysis and Its Reduction Techniques in Deep Submicron TechnologyIJERA Editor
This paper presents a detailed conceptual analysis of IR Drop effect in deep submicron technologies and its reduction techniques. The IR Drop effect in power/ground network increases rapidly with technology scaling. This affects the timing of the design and hence the desired speed. It is shown that in present day designs, using well known reduction techniques such as wire sizing and decoupling capacitor insertion, may not be sufficient to limit the voltage fluctuations and hence, two more important methods such as selective glitch reduction technique and IR Drop reduction through combinational circuit partitioning are discussed and the issues related to all the techniques are revised.
Power gating is the main power reduction techniques for the static power. As long as technology scaling is taking place, static power becomes paramount important factor to the VLSI designs.Therefore Power gating is the recent power reduction technique that is actively in research areas.
Nanometer layout handbook at high speed designMinho Park
I made this contents for whom is about to layout own's IC design. I think it would be helpful to consider layouts about high speed Rx / Tx.
Specially it was aimed giga hertz bandwidth I/O with its ESD protection (I am still working on that items to rearrange with my knowledge to my experiences)
I showed up all references and all images (except originals) are belong to own's copy rights.
Hi, im Perlis polytechnic student, and now i undergo last semester already. And i taken one interesting subject is CMOS IC design. So this is one of lab work that i uploading. Using L-Edit to design NAND gate.
This ppt is about full adder design using pass transistor logic. This circuit describe power reduction using proposed cell as standard element in technology library design for ultra low power. we provide guidance to m.tech students in thier final year research projects. We assist on IEEE projects to M.tech or PhD students. Students can contact us for VLSI Projects, Antenna Projects, MATLAB Projects
Bundle conductors in transmission line chandan kumar
Bundled Conductors are used in transmission lines where the voltage exceeds 230 kV.
At such high voltages, ordinary conductors will result in excessive corona and noise which may affect communication lines.
The increased corona will result in significant power loss. Bundle conductors consist of three or four conductors for each phase.
The conductors are separated from each other by means of spacers at regular intervals. Thus, they do not touch each other.
About
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Technical Specifications
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
Key Features
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface
• Compatible with MAFI CCR system
• Copatiable with IDM8000 CCR
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
Application
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
CFD Simulation of By-pass Flow in a HRSG module by R&R Consult.pptxR&R Consult
CFD analysis is incredibly effective at solving mysteries and improving the performance of complex systems!
Here's a great example: At a large natural gas-fired power plant, where they use waste heat to generate steam and energy, they were puzzled that their boiler wasn't producing as much steam as expected.
R&R and Tetra Engineering Group Inc. were asked to solve the issue with reduced steam production.
An inspection had shown that a significant amount of hot flue gas was bypassing the boiler tubes, where the heat was supposed to be transferred.
R&R Consult conducted a CFD analysis, which revealed that 6.3% of the flue gas was bypassing the boiler tubes without transferring heat. The analysis also showed that the flue gas was instead being directed along the sides of the boiler and between the modules that were supposed to capture the heat. This was the cause of the reduced performance.
Based on our results, Tetra Engineering installed covering plates to reduce the bypass flow. This improved the boiler's performance and increased electricity production.
It is always satisfying when we can help solve complex challenges like this. Do your systems also need a check-up or optimization? Give us a call!
Work done in cooperation with James Malloy and David Moelling from Tetra Engineering.
More examples of our work https://www.r-r-consult.dk/en/cases-en/
Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
A case study of the used of Advanced Process Control at the Wastewater Treatment works at Lleida in Spain
A look back on an article on smart wastewater networks in order to see how the industry has measured up in the interim around the adoption of Digital Transformation in the Water Industry.
Quality defects in TMT Bars, Possible causes and Potential Solutions.PrashantGoswami42
Maintaining high-quality standards in the production of TMT bars is crucial for ensuring structural integrity in construction. Addressing common defects through careful monitoring, standardized processes, and advanced technology can significantly improve the quality of TMT bars. Continuous training and adherence to quality control measures will also play a pivotal role in minimizing these defects.
COLLEGE BUS MANAGEMENT SYSTEM PROJECT REPORT.pdfKamal Acharya
The College Bus Management system is completely developed by Visual Basic .NET Version. The application is connect with most secured database language MS SQL Server. The application is develop by using best combination of front-end and back-end languages. The application is totally design like flat user interface. This flat user interface is more attractive user interface in 2017. The application is gives more important to the system functionality. The application is to manage the student’s details, driver’s details, bus details, bus route details, bus fees details and more. The application has only one unit for admin. The admin can manage the entire application. The admin can login into the application by using username and password of the admin. The application is develop for big and small colleges. It is more user friendly for non-computer person. Even they can easily learn how to manage the application within hours. The application is more secure by the admin. The system will give an effective output for the VB.Net and SQL Server given as input to the system. The compiled java program given as input to the system, after scanning the program will generate different reports. The application generates the report for users. The admin can view and download the report of the data. The application deliver the excel format reports. Because, excel formatted reports is very easy to understand the income and expense of the college bus. This application is mainly develop for windows operating system users. In 2017, 73% of people enterprises are using windows operating system. So the application will easily install for all the windows operating system users. The application-developed size is very low. The application consumes very low space in disk. Therefore, the user can allocate very minimum local disk space for this application.
Sachpazis:Terzaghi Bearing Capacity Estimation in simple terms with Calculati...Dr.Costas Sachpazis
Terzaghi's soil bearing capacity theory, developed by Karl Terzaghi, is a fundamental principle in geotechnical engineering used to determine the bearing capacity of shallow foundations. This theory provides a method to calculate the ultimate bearing capacity of soil, which is the maximum load per unit area that the soil can support without undergoing shear failure. The Calculation HTML Code included.
Final project report on grocery store management system..pdfKamal Acharya
In today’s fast-changing business environment, it’s extremely important to be able to respond to client needs in the most effective and timely manner. If your customers wish to see your business online and have instant access to your products or services.
Online Grocery Store is an e-commerce website, which retails various grocery products. This project allows viewing various products available enables registered users to purchase desired products instantly using Paytm, UPI payment processor (Instant Pay) and also can place order by using Cash on Delivery (Pay Later) option. This project provides an easy access to Administrators and Managers to view orders placed using Pay Later and Instant Pay options.
In order to develop an e-commerce website, a number of Technologies must be studied and understood. These include multi-tiered architecture, server and client-side scripting techniques, implementation technologies, programming language (such as PHP, HTML, CSS, JavaScript) and MySQL relational databases. This is a project with the objective to develop a basic website where a consumer is provided with a shopping cart website and also to know about the technologies used to develop such a website.
This document will discuss each of the underlying technologies to create and implement an e- commerce website.
Hybrid optimization of pumped hydro system and solar- Engr. Abdul-Azeez.pdffxintegritypublishin
Advancements in technology unveil a myriad of electrical and electronic breakthroughs geared towards efficiently harnessing limited resources to meet human energy demands. The optimization of hybrid solar PV panels and pumped hydro energy supply systems plays a pivotal role in utilizing natural resources effectively. This initiative not only benefits humanity but also fosters environmental sustainability. The study investigated the design optimization of these hybrid systems, focusing on understanding solar radiation patterns, identifying geographical influences on solar radiation, formulating a mathematical model for system optimization, and determining the optimal configuration of PV panels and pumped hydro storage. Through a comparative analysis approach and eight weeks of data collection, the study addressed key research questions related to solar radiation patterns and optimal system design. The findings highlighted regions with heightened solar radiation levels, showcasing substantial potential for power generation and emphasizing the system's efficiency. Optimizing system design significantly boosted power generation, promoted renewable energy utilization, and enhanced energy storage capacity. The study underscored the benefits of optimizing hybrid solar PV panels and pumped hydro energy supply systems for sustainable energy usage. Optimizing the design of solar PV panels and pumped hydro energy supply systems as examined across diverse climatic conditions in a developing country, not only enhances power generation but also improves the integration of renewable energy sources and boosts energy storage capacities, particularly beneficial for less economically prosperous regions. Additionally, the study provides valuable insights for advancing energy research in economically viable areas. Recommendations included conducting site-specific assessments, utilizing advanced modeling tools, implementing regular maintenance protocols, and enhancing communication among system components.
Overview of the fundamental roles in Hydropower generation and the components involved in wider Electrical Engineering.
This paper presents the design and construction of hydroelectric dams from the hydrologist’s survey of the valley before construction, all aspects and involved disciplines, fluid dynamics, structural engineering, generation and mains frequency regulation to the very transmission of power through the network in the United Kingdom.
Author: Robbie Edward Sayers
Collaborators and co editors: Charlie Sims and Connor Healey.
(C) 2024 Robbie E. Sayers
1. Passive Device Fabrication in IC
By
Prof. Abhishek Kadam
(M.Tech Electronics)
Recourse's Credit : RF Microelectronics By B. Razavi
2. Contents
• Fabrication of inductors
• fabrication of transformers
• fabrication of varactors
• fabrication of fixed value capacitors
3. Need of Inductors
• Modern RF design needs many inductors
• This topology suffers from two serious drawbacks
• the bandwidth at node X is limited to 1/[(𝑅 𝐷| 𝑟𝑂1
𝐶 𝐷 ]
• the voltage headroom trades with the voltage gain, g 𝑚1
(𝑅 𝐷| 𝑟𝑂1
• CMOS technology scaling tends to improve the former but at the cost of the latter
• For example, in 65-nm technology with a 1-V supply, the circuit provides a
bandwidth of several gigahertz but a voltage gain in the range of 3 to 4.
4. Need of Inductors
• 𝐿 𝐷 resonates with 𝐶 𝐷, allowing operation at much higher
frequencies (albeit in a narrow band)
• 𝐿 𝐷 sustains little dc voltage drop, the circuit can comfortably
operate with low supply voltages while providing a reasonable
voltage gain (e.g., 10).
5. Drawback of using off chip Inductors
• External inductors present cost penalties
• The bond wires and package pins connecting the chip to the outside world
may experience significant coupling creating crosstalk between different
parts of the transceiver.
• external connections introduce parasitics that become significant at higher
frequencies.
• it is difficult to realize differential operation with external loads because of
the poor control of the length of bond wires
6. Disadvantages of on chip inductors
• On-chip inductors exhibit a lower quality
factor than their off-chip counterparts, leading
to higher “phase noise” in oscillators
• Unlike resistors and Capacitors, inductors are
much more difficult to model
7. INDUCTORS
• Basic Structure
– Integrated inductors are typically realized as metal
spirals
– Owing to the mutual coupling between every two
turns, spirals exhibit a higher inductance than a
straight line having the same length
– To minimize the series resistance and the parasitic
capacitance, the spiral is implemented in the top
metal layer
8. INDUCTORS
• Fig shows typical spiral structure of Integrated inductor
• There are three turns AB, BC and CD
• Considering mutual inductance Total inductance is given by
• 𝐿 𝑡𝑜𝑡𝑎𝑙 = 𝐿1 + 𝐿2 + 𝐿3 + 𝑀12 + M13 + M23
• Due to geometry inner turns exhibit lower inductance
• Mutual inductance M13 is smaller than 𝑀12
9. Two-dimensional square spiral
• A two-dimensional square spiral is fully
specified by four quantities
– The outer dimension, 𝐷 𝑜𝑢𝑡
– The line width, W
– The line spacing, S
– Number of turns, N
13. Inductance Equation
• An empirical formula that has less than 10% error
for inductors in the range of 5 to 50 nH is given by
Where 𝐴 𝑚 is metal area and 𝐴 𝑡𝑜𝑡𝑎𝑙 is total inductor
area
14. For N turns 𝑙 𝑡𝑜𝑡 is given by
Calculate 𝑙 𝑡𝑜𝑡 for fig
16. • a given length of wire yields roughly a
constant inductance regardless of how it is
“wound.”
17. Parasitic Capacitances
• As a planar structure built upon a substrate,
spiral inductors suffer from parasitic
capacitances of two types
1. The metal line forming the inductor exhibits
parallel plate and fringe capacitances to the
substrate
18. 2.The adjacent turns also bear a fringe
capacitance, which equivalently appears in
parallel with each segment
19. Loss mechanism
Suppose the metal line forming an inductor exhibits a series resistance
The Q may be defined as the ratio of the desirable impedance, 𝐿1 𝜔0, and the
undesirable impedance, 𝑅 𝑆
𝑄 = 𝐿1 𝜔0/𝑅 𝑠
20. Skin Effect
• At high frequencies, the current through a conductor prefers
to flow at the surface.
• The actual distribution of the current follows an exponential
decay from the surface of the conductor inward, 𝐽 𝑠 =
𝐽0exp(2𝑥/𝛿), where 𝐽0 denotes the current density (in 𝐴/𝑚2
)
at the surface, and δ is the “skin depth.” The value of δ is
given by
𝛿 = 1/ 𝜋𝑓𝜇σ
• The extra resistance of a conductor due to the skin effect is
equal to 𝑅 𝑠𝑘𝑖𝑛 = 1/𝜎𝛿
21. • In spiral inductors, the proximity of adjacent
turns results in a complex current distribution.
• the current may concentrate near the edge of
the wire. To understand this “current
crowding” effect, consider the more detailed
diagram shown below
22. • The current in one turn creates a time-varying
magnetic field, B, that penetrates the other
turns, generating loops of current Called
“eddy currents,”
24. • Current crowding also alters the inductance and
capacitance of spiral geometries. Since the current is
pushed to the edge of the wire, the equivalent
diameter of each turn changes slightly, yielding an
inductance different from the low-frequency value
26. • The principal drawback of symmetric inductors is
their large interwinding capacitance
27. • How do we reduce the interwinding
capacitance?
• We can increase the line-to-line spacing, S,
but, for a given outer dimension, this results in
smaller inner turns and hence a lower
inductance.
• As a rule of thumb, we choose a spacing of
approximately three times the minimum
allowable value.
28. Inductors with Ground Shield
• The magnetic coupling from an inductor to the substrate can be
understood with the aid of basic electromagnetic laws:
1. Ampere’s law states that a current flowing through a conductor generates a magnetic
field around the conductor;
2. Faraday’s law states that a time-varying magnetic field induces a voltage, and hence a
current if the voltage appears across a conducting material;
3. Lenz’s law states that the current induced by a magnetic field generates another
magnetic field opposing the first field.
• Ampere’s and Faraday’s laws readily reveal that, as the current through an
inductor varies with time, it creates an eddy current in the substrate
• Lenz’s law implies that the current flows in the opposite direction.
29. • both the electric coupling and the magnetic coupling to the
substrate are eliminated if a grounded conductive plate is
placed under the spiral
• This method indeed reduces the path resistance seen by both
displacement and eddy currents but the equivalent
inductance also falls with 𝑅 𝑠𝑢𝑏,
• we observed that eddy currents in a continuous shield
drastically reduce the inductance and the Q
30. • The shield can provide a low-resistance termination for electric field
lines even if it is not continuous
• a “patterned” shield, i.e., a plane broken periodically in the
direction perpendicular to the flow of eddy currents, receives most
of the electric field lines without reducing the inductance.
• A small fraction of the field lines sneak through the gaps in the
shield and terminate on the lossy substrate. Thus, the width of the
gaps must be minimized.
• The use of a patterned shield may increase the Q by 10 to 15% but
the improvement comes at the cost of higher capacitance
31. • Stacked Inductors
– At frequencies up to about 5 GHz, inductor values
encountered in practice fall in the range of five to several
tens of nanohenries
– If realized as a single spiral, such inductors occupy a large
area and lead to long interconnects between the circuit
blocks.
– In stacked Inductors place two or more spirals in series,
obtaining a higher inductance not only due to the series
connection but also as a result of strong mutual coupling.
32. Transformers
• Integrated transformers can perform a number of useful
functions in RF design:
1. impedance matching
2. feedback or feed forward with positive or negative polarity
3. ac coupling between stages.
4. single-ended to differential conversion or vice versa
• A well-designed transformer must exhibit the following:
1. low series resistance in the primary and secondary windings
2. high magnetic coupling between the primary and the secondary
3. low capacitive coupling between the primary and the secondary,
4. Low Parasitic capacitances to the substrate.
33. Transformer Structures
• An integrated transformer generally comprises
two spiral inductors with strong magnetic
coupling.
34. • The transformer structure of previous diagram
suffers from low magnetic coupling, an
asymmetric primary, and an asymmetric
secondary.
• To remedy the former, the number of turns
can be increased as shown in fig below but at
the cost of higher capacitive coupling
35. • It is possible to construct planar transformers
having a turns ratio greater than unity
36. • Figure below shows two other examples of planar
transformers. Here, two asymmetric spirals are inter
wound to achieve a high coupling factor.
37. • Transformers can also be implemented as three-
dimensional structures. Similar to the stacked inductors
• It is important to recognize the following attributes
– the alignment of the primary and secondary turns results in a
slightly higher magnetic coupling factor here than in the planar
transformers
– unlike the planar structures, the primary and the secondary can
be symmetric and identical
– the overall area occupied by 3D transformers is less than that of
their planar counterparts
38. • Another advantage of stacked transformers is
that they can readily provide a turns ratio
higher than unity
• the idea is to incorporate multiple spirals in
series to form the primary or the secondary.
39. • Stacked transformers must, however, deal
with two issues
– the lower spirals suffer from a higher resistance
due to the thinner metal layers.
– the capacitance between the primary and
secondary is larger here than in planar
transformers
• To reduce this capacitance, the primary and secondary
turns can be “staggered,” thus minimizing their overlap
40. VARACTORS
• A varactor is a voltage-dependent capacitor.
• Two attributes of varactors become critical in
oscillator design:
– the capacitance range, i.e., the ratio of the
maximum and minimum capacitances that the
varactor can provide 𝐶 𝑚𝑎𝑥 / 𝐶 𝑚𝑖𝑛
– the quality factor of the varactor, which is limited
by the parasitic series resistances within the
structure
41. • In older generations of RF ICs, varactors were
realized as reverse-biased pn junctions
42. The capacitance range and Q of pn junctions
• At a reverse bias of 𝑉𝐷, the junction capacitance, 𝐶𝑗, is
given by
where 𝐶𝑗0
is the capacitance at zero bias, 𝑉0 the built-in
potential, and m an exponent around 0.3 in integrated
structures
• 𝐶𝑗 has very weak dependence on 𝑉𝐷
• In today’s technology with 𝑉𝐷𝐷 ≈ 1𝑉,𝐶𝑗max
/𝐶𝑗m𝑖𝑛
=1.23
43. • The Q of a pn-junction varactor is given by the total
series resistance of the structure.
• this resistance is primarily due to the n-well and can
be minimized by selecting minimum spacing
between the 𝑛+
and 𝑝+
contacts
• to lower the resistance in two dimensions each 𝑝+
region can be surrounded by an 𝑛+ ring.
44. • Due to the two-dimensional nature of the flow, it is difficult to
determine or compute the equivalent series resistance of the
structure
• This issue arises partly because the sheet resistance of the n-
well is typically measured by the foundry for contacts having a
spacing greater than the depth of the n-well
• Since the current path in this case is different from that in Fig.
below the n-well sheet resistance cannot be directly applied
to the calculation of the varactor series resistance
45. • In modern RF IC design, MOS varactors have
supplanted their pn-junction counterparts.
• A regular MOSFET exhibits a voltage-dependent
gate capacitance but the non monotonic behavior
limits the design flexibility.
46. • A simple modification of the
MOS device avoids the before
mentioned issues
• Accumulation-mode MOS
varactor are shown in fig.
near
• this structure is obtained by
placing an NMOS transistor
inside an n-well
– If 𝑉𝐺 < 𝑉𝑆, then the electrons in
the n-well are repelled from the
silicon/oxide interface and a
depletion region is formed and
the equivalent capacitance is
given by the series combination
of the oxide and depletion
capacitances
47. – As 𝑉𝐺 exceeds 𝑉𝑆, the interface
attracts electrons from the 𝑛+
source/drain terminals,
creating a channel
– The overall capacitance
therefore rises to that of the
oxide, behaving as shown
• These varactors operate with low supply voltages better
than their pn-junction counterparts.
• Another advantage of accumulation-mode MOS
varactors is that, unlike pn junctions, they can tolerate
both positive and negative voltages.
48. • we approximate the characteristic of
Accumulation-mode MOS varactor by
Here, a and 𝑉0 allow fitting for the intercept and the slope,
respectively, and 𝐶 𝑚𝑖𝑛 and 𝐶 𝑚𝑎𝑥 include the gate-drain and gate-
source overlap capacitance.
49. • The Q of MOS varactors is determined by the
resistance between the source and drain
terminals
• This resistance and the capacitance are
distributed from the source to the drain and
can be approximated by the lumped model
depicted below
50. • Finding 𝐶𝑡𝑜𝑡 𝑎𝑛𝑑 𝑅𝑡𝑜𝑡
• Let us first consider only one-half of the structure as
shown and We turn the circuit upside down, arriving
at the more familiar topology illustrated
51. For general T-line shown below, input impedance, 𝑍𝑖𝑛,
is given by
Thus for equivalent MOS structure 𝑍𝑖𝑛 is given by
52. • At frequencies well below 1/(𝑅𝑡𝑜𝑡 𝐶𝑡𝑜𝑡/4), the
argument of 𝐭𝐚𝐧𝐡 is much less than unity,
allowing the approximation,
It follows
Hence
53. • It is desirable to maximize the Q of varactors for
oscillator design.
• From our foregoing study of MOS varactors, we
conclude that the device length (the distance
between the source and drain) must be minimized
• but for a minimum channel length, the overlap
capacitance between the gate and source/drain
terminals becomes a substantial fraction of the
overall capacitance, limiting the capacitance range
• yielding a Low ratio of
54. CONSTANT CAPACITORS
• RF circuits employ constant capacitors for various
purposes
1. To adjust the resonance frequency of LC tanks
2. to provide ac coupling between stages
3. to bypass the supply rail to ground
• MOS Capacitors
– MOSFETs configured as capacitors offer the highest
density in integrated circuits because 𝐶 𝑜𝑥 is larger
than other capacitances in CMOS processes.
– But the use of MOS capacitors entails two issues
• To provide the maximum capacitance, the device requires
a 𝑉𝐺𝑆 higher than the threshold voltage
• The channel resistance limits the Q of MOS capacitors at
high frequencies
55. • Consider the circuit given
• 𝑉𝐺𝑆3
= 𝑉𝐷𝐷 − 𝑉𝐺𝑆22
Thus for Low 𝑉𝐷𝐷, 𝑉𝐺𝑆3
is
Low and Hence Due to Low Overdrive Voltage
𝑅 𝑜𝑛 is high
• For these reasons, MOS capacitors rarely serve
as coupling devices
56. • Other application of MOS capacitors is in
supply bypass
• the supply line may include significant bond wire inductance,
allowing feedback from the second stage to the first at high
frequencies
• The bypass capacitor, M3, creates a low impedance between
the supply and the ground, suppressing the feedback.
• if the equivalent series resistance of the device becomes
comparable with the reactance of its capacitance, then the
bypass impedance may not be low enough to suppress the
feedback.
57. • Comment of 𝑅 𝑜𝑛 of the following citcuit
modification
58. Metal-Plate Capacitors
• If the Q or linearity of MOS capacitors is
inadequate, metal-plate capacitors can be
used instead.
• The parallel plate structure is shown below
However, even with all metal layers and a
poly layer, parallel-plate structures achieve
less capacitance density than MOSFETs do.
For example,
with nine metal layers in 65-nm
technology, the former provides a density
of about 1.4 fF/𝜇𝑚2 and the latter, 17 fF/
𝜇𝑚2
59. • Parallel-plate geometries also suffer from a parasitic capacitance to
the substrate
• In a typical process, this value reaches 10%, leading to serious
difficulties in circuit design.
• To alleviate the above issue, only a few top metal layers can be
utilized
60. • An alternative geometry utilizes the lateral
electric field between adjacent metal lines to
achieve a high capacitance density
This “fringe” capacitor consists of narrow metal lines with the
minimum allowable spacing