Latch Up In CMOS

What is latch up in CMOS design and ways to prevent it?

A Problem which is inherent in the p-well and n-well processes is due to relatively large number of junctions which are formed in these structures, the consequent presence of parasitic diodes and transistors.

Latch-up is a condition in which the parasitic components give rise to the Establishment of low resistance conducting path between VDD and VSS with Disastrous results

Latch-up may be induced by glitches on the supply rails or by incident radiation.

Latch-up pertains to a failure mechanism wherein a parasitic thyristor (such as a parasitic silicon controlled rectifier, or SCR) is inadvertently created within a circuit, causing a high amount of current to continuously flow through it once it is accidentally triggered or turned on. Depending on the circuits involved, the amount of current flow produced by this mechanism can be large enough to result in permanent destruction of the device due to electrical overstress (EOS).

Preventions for Latch-Up

• by adding tap wells, for example in an Inverter for NMOS add N+ tap in n-well and connect it to Vdd, and for PMOS add P+ tap in p-substrate and connect it to Vss.
• an increase in substrate doping levels with a consequent drop in the value of  Rs.
• reducing Rp by control of fabrication parameters and by ensuring a low contact resistance to Vss.
• and the other is by introducing of guard rings.....

Latchup in Bulk CMOS

A byproduct of the Bulk CMOS structure is a pair of parasitic bipolar transistors. The collector of each BJT is connected to the base of the other transistor in a positive feedback structure. A phenomenon called latchup can occur when (1) both BJT's conduct, creating a low resistance path between Vdd and GND and (2) the product of the gains of the two transistors in the feedback loop, b1 x b2, is greater than one. The result of latchup is at the minimum a circuit malfunction, and in the worst case, the destruction of the device.

  Cross section of parasitic transistors in Bulk CMOS

 Equivalent Circuit

Latchup may begin when Vout drops below GND due to a noise spike or an improper circuit hookup (Vout is the base of the lateral NPN Q2). If sufficient current flows through Rsub to turn on Q2 (I Rsub > 0.7 V ), this will draw current through Rwell. If the voltage drop across Rwell is high enough, Q1 will also turn on, and a self-sustaining low resistance path between the power rails is formed. If the gains are such that b1 x b2 > 1, latchup may occur. Once latchup has begun, the only way to stop it is to reduce the current below a critical level, usually by removing power from the circuit.

The most likely place for latchup to occur is in pad drivers, where large voltage transients and large currents are present.

Preventing latchup

Fab/Design Approaches:

1. Reduce the gain product b1 x b1

• move n-well and n+ source/drain farther apart increases width of the base of Q2 and reduces gain beta2 ­> also reduces circuit density
• buried n+ layer in well reduces gain of Q1

    2. Reduce the well and substrate resistances, producing lower voltage drops

· higher substrate doping level reduces Rsub

· reduce Rwell by making low resistance contact to GND

· guard rings around p- and/or n-well, with frequent contacts to the rings, reduces the parasitic resistances.

CMOS transistors with guard rings

Systems Approaches:

1. Make sure power supplies are off before plugging a board. A "hot plug in" of an unpowered circuit board or module may cause signal pins to see surge voltages greater than 0.7 V higher than Vdd, which rises more slowly to is peak value. When the chip comes up to full power, sections of it could be latched.
2. Carefully protect electrostatic protection devices associated with I/O pads with guard rings. Electrostatic discharge can trigger latchup. ESD enters the circuit through an I/O pad, where it is clamped to one of the rails by the ESD protection circuit. Devices in the protection circuit can inject minority carriers in the substrate or well, potentially triggering latchup.
3. Radiation, including x-rays, cosmic, or alpha rays, can generate electron-hole pairs as they penetrate the chip. These carriers can contribute to well or substrate currents.
4. Sudden transients on the power or ground bus, which may occur if large numbers of transistors switch simultaneously, can drive the circuit into latchup. Whether this is possible should be checked through simulation.

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Do U Know? Mobile devices said to consume more energy on storage tasks

Do u know that “Flash storage takes power to write - a 20 volt jolt to each cell - but needs almost none to maintain. The real power hog is the inefficient storage software stack that eats 200 times the power required for the hardware.”

Given the always-on mobile infrastructure - background updates, instant messages, email, updates, file sync, logging and more - lots of background storage I/O is happening all the time. And it's eating your device's power budget.

Researchers from Microsoft and the University of California at San Diego benchmarked how Android and Windows RT mobile devices used energy for storing data. They focused on activities that occur with the screen off, since displays are a major power consumer when lit. "Measurements across a set of storage-intensive micro benchmarks show that storage software may consume as much as 200x more energy than storage hardware on an Android phone and a Windows RT tablet," the research team wrote in a paper. "The two biggest energy consumers are encryption and managed language environments."

Results
On Windows RT they found that the OS/CPU/DRAM overhead was between 5 and 200 times the power used by the flash storage itself, depending on how DRAM power use was allocated. File system APIs, the language environment and encryption drove the CPU power consumption during I/O. Full disk encryption - protecting user data - incurred 42 percent of CPU utilization.

On an Android phone, the encryption penalty is even worse: 2.6–5.9x more energy per KB over non-encrypted I/O.

For applications, the team found that on Windows RT, the energy overhead in a managed environment is 12.6–18.3 percent while overhead on Android is between 24.3–102.1 percent. It appears that Android's algorithms are not optimized for application I/O power efficiency.

Assertion Debugging in Questa – few tips

Playing around debugging some complex assertions in Qeusta? Here are some tips:

1. Use vsim –assertdebug

2. Add –novopt for trivial code containing assertions + stim alone as otherwise many signals get optimized away. On real designs, perhaps you are better off with +acc* (Read doc for more)

3. Once the GUI comes up, the assertions are not listed in its own browser – ideally I would have liked to see a menu item under “Tools” menu. But it is hidden under “View –> Coverage –> Assertions” – GOK why! (GOK – God Only Knows)  :)

4. Before starting simulation, enable ATV

5. After sim one can do “view ATV” for advanced debug!

 

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Motorola Moto G Now In India

Motorola's much awaited Android smartphone Moto G has been launched in India at a price point of Rs 12,499 for the 8GB variant and Rs 13,999 for the 16GB storage variant.
The company took to twitter to confirm the news. "Moto G is now available in India, exclusively on Flipkart. Order it today to take advantage of launch offers," it said. 
Available exclusively on Flipkart initially, As a promotional gesture, the online retailer is offering Rs.500 discounts on e-Books, Rs.1000-off on the clothing, flat 70-percent off on cover-cases and some lucky  consumers will also stand a chance to win 100-percent cash back (in terms of store credit) with the purchase of Moto G. [offer is for limited period only]

At the moment the 16GB model has been listed on Flipkart ( with 1 year manufacturer warranty for Phone and 6 months warranty for in the box accessories Motorola India Warranty and Free Transit Insurance.)

Apart from Flipkart, Snapdeal is also retailing Moto G. As of now, the pre-order booking has been closed due non-availability of stocks. It recorded 1000 orders within 2 hours of listing the Moto G on 4 February, reported BGR.
Feature-rich Moto G flaunts a 4.5-inch HD (1270x720p) LCD screen protected by Corning Gorilla Glass 3 shield and houses dual-SIM slots. It run on the Android v4.3 Jelly Bean (guaranteed to get KitKat update) powered by a Qualcomm Snapdragon 400 series quad-core processor backed by 1GB RAM and comes in 8GG and 16GB variants.
With the launch, Motorola Moto G is expected to give a stiff challenge to low-cost Indian smartphones like Micromax Canvas Turbo Mini A200, Lava Iris Pro 30, Karbonn Titanium S5 plus and others.

Motorola G Specifications:

Model	Motorola Moto G (Dual-SIM model confirmed for India)
Display	4.5-inch HD (1270x720p) LCD screen with 329 ppi (pixels per inch), comes protected with Corning Gorilla Glass 3 shield.
OS	Android v4.3, Guaranteed update of Android v4.4 KitKat
Processor	Qualcomm Snapdragon 400 series quad-core processor with 1.2GHz CPU speed
RAM	1GB
Storage capacity	8GB/16 GB variants ( no microSD card slot)
Camera	Main: 5.0-megapixel camera with LED flash Front: 1.3-megapixel camera
Network	3G
Battery	2,070 mAh
Add-ons	Wi-Fi (802.11 b/g/n),Bluetooth v4.0, USB, NFC, GPS
Dimensions	129.9 x 65.9 x 11.6 mm
Weight	143 g
Price	8GB: Rs.12,999 & 16GB: Rs.14,499

ModelSim VS QuestaSim

We as an ASIC Engineer are frequently using different simulators for our simulation activity. At present time we are frequently using modelsim/Questa and vcs. These are the industry popular and well proven simulators.
We have seen people who are using modelsim / Questa simulator from Mentors but dont really know the exact difference between them.
We have captured some difference between Questa and Modelsim. Though both are simulators from the Mentor Graphics there are some differences between them. Below are the differences We captured :

ModelSim is Mentor Graphics HDL simulator. Questa is Mentor Graphics advanced verification platform that uses ModelSim as its core simulation engine.

Features of the two tools can be grouped into five categories and compared as follows:

1. Language Support
- ModelSim supports SystemVerilog IEEE 1800 for Design only, as well as VHDL (1987, 1993, 2002), Verilog (1995, 2001, 2005), as well as options for mixed language and language neutral licensing and support for SystemC 2.2 IEEE 1666/OSCI 2.2.
- Questa supports all of this as well as SystemVerilog IEEE 1800 for Verification, mixed language licensing (Questa is by default language neutral), PSL IEEE 1850, and SystemC 2.2 IEEE 1666/OSCI 2.2 as standard features.

2. Simulation
- ModelSim supports a single-kernel simulation engine, Verilog RTL & gate level performance optimizations, VHDL RTL & VITAL performance optimizations, performance and memory profiler, separate elaboration, waveform management tool set, VCD and extended VCD support, VCD re-simulation, batch mode simulation, integrated simulation, checkpoint & restore,
- Questa’s simulation support is identical to ModelSim’s

3. Design Entry, Debug, and Analysis
- ModelSim supports an HDL editor, integrated project manager, source code templates and wizards, interactive and post-simulation debug, dataflow graphical and textual causality traceback, source annotation, memory window, extra standalone viewer, multiple waveform windows, waveform compare, C Debugger and transaction viewing for SystemC.
- Questa supports all of this and the C debugger and transaction viewing for SystemC and SystemVerilog are standard parts of the product.

4. Advanced Verification Methods
- ModelSim does not support any advanced verification features.
- Questa supports assertion-based verification (including a library of pre-written assertions called Questa Verification Library or QVL, and an assertion thread debugger), automated test stimulus generation via a constraint solver engine, and PowerAware RTL verification supporting both CPF and UPF formats.

5 Verification Management and Coverage
- ModelSim supports Code Coverage (it is included in ModelSim SE, and an option to other versions of ModelSim).
-Questa supports code coverage along with functional coverage, a unified coverage database (UCDB), coverage viewing, test ranking, and test plan tracking

Hope you find this information useful.

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VHDL Tutorial: The Beginner’s Guide to State Machines - VHDL

VHDL Tutorial: The Beginner’s Guide to State Machines - VHDL: Implementing state machines in VHDL is fun and easy provided you stick to some fairly well established forms.

Intel Introduces 2 Ultra-Low-Power Mobile Chips

Intel has introduced nine Core i5 and Core i7 "Haswell" mobile processors, including two ultra-low-voltage processors for Ultrabooks, the 2-gigahertz i5-4310U and the 1.5GHz 4360U. The 4360U has the company's HD 5000 graphics capability, according to Intel.

The Haswell rollout has solidified the company's dominance in the computer chip business (including what it claims are record sales of desktop Core i7 CPUs), especially on the mobile side of things. Intel is looking to further its advantage with the release of a new batch of fourth-generation Core processors designed for notebooks.

The nine new mobile Haswell CPUs are a mix of Core i5 and i7 chips that will power performance portables, though a couple are ultra-low-voltage (ULV) processors that can be used in Ultrabooks.The cheapest new one is the i5-4310M at $225 (prices will factor into the cost of a new notebook, as the laptop upgrade market is neglible); its two cores run at 2.7GHz. For about $40 more, the i5-4340M goes to 2.9GHz, while for svelte systems, there's the 2GHz i5-4310U and the 1.5GHz 4360U. Despite the slower clock speed, the 4360U costs more than the other ULV chip because it makes use of Intel's more powerful HD 5000 graphics.

Even though these are new processors, they aren't a quantum leap beyond their predecessors. Because they are clocked about 100MHz higher than the initial Haswell CPUs, that's only about a few percentage points better in performance. But who's going to argue with faster, especially when it's going to be baked into new laptops over the next few months.

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