Custom Analog ICs Made Simple
Bob Frostholm — JVD, Inc
Before the popularization of the term Application Specific Integrated Circuits, (ASICs), they were called Custom Chips. Most semiconductor companies accommodated requests to develop and produce them if they were already doing a sizeable business with the customer AND if the volume of the customer’s chip was significant. Most of the time it wasn’t and the customer went away disappointed…until…
…Hans Camenzind, a Swiss emigre analog guru who invented the most successful circuit in electronics history (the NE555 Timer) and introduced the concept of phase-locked loop to IC design (NE565 Single chip PLL) left Signetics in 1971 to start a semi-custom analog IC company called InterDesign. These were metal mask programmable arrays of analog building blocks (op amps, comparators, current sources, etc.)… Basically a very early primitive version of todays via configurable arrays, and similarly well suited for very low volume applications.
Hans showed the world that there is always a creative way around a problem and showed the world that it was relatively easy to make custom analog ICs for low volume applications.
Flash forward 45+ years and today, when engineers hear the term ASIC, the mind conjures up visions of massive digital chips containing tens or hundreds of millions of logic gates. Unlike multi-function standard product ICs such as a micro-controller that can find its way into a wide variety of applications, ASICs are designed for one specific application and generally for one specific product or product family. The first digital ASICs were built using a standard cell library consisting of fixed-height, variable-width ‘tiles’ or ‘cells’ containing digital logic functions based on Boolean Algebra. The ability to reuse these blocks over and over saved time and money when designing a custom logic IC.
That’s not so easy with analog functions for many reasons. Parasitic capacitances, a/c coupling across metal interconnects and much more dictate that the physical layout of an analog chip is as critical, if not more so, than the actual circuit design. Automatic place and route tools can help to a certain point, but after that the designer and layout engineer need to work their magic to ensure the proper performance of the IC.
Analog ICs were initially comprised of a pair of matched transistors and soon expanded to include rudimentary Op Amps, Voltage Regulators, Comparators, Timers and much more. Analog applications typically involve much higher voltages than their digital counterparts so these ICs needed their own unique set of wafer fabrication processes. More recently, market demands for smaller size, higher speeds and lower power consumption have forced a merging of analog and digital functionality on a single silicon chip. Cells consisting of the basic analog building blocks discussed above were created and added to the digital libraries. These Analog cells were restricted to the digital fab processes developed for predominately logic applications.
Today, most ASIC companies offer some degree of analog functionality as a part of their services. In many cases, the analog functions are mimicked with digital design techniques. In others, compromises to the analog functionality must be made to facilitate the use of standard library cells that are designed to yield well in the fab processes developed for high speed, high density, low power digital designs. Often, these chips are referred to as Mixed-signal ASICs or as big “D”, little “A” ASICs, meaning high digital content and minimal analog content.
Analog ASICs play a critical role in our lives. Without them, none of the portable electronic devices we use in our daily lives would exist. Imagine a world without Cell Phones, Flat Panel TVs, (bye-bye Sports Bars), Lane Change and Parking Sensors, and Navigation Systems. Building them with standard products would make them prohibitively expensive and for the cell phone, physically impossible to carry in our purses or pockets. Every automobile contains dozens of ASIC chips for everything from climate control to airbag deployment; suspension control to entertainment systems. ASICs also play important roles in applications for hospital medical equipment, eMeters, home appliances such as washers and dryers, scuba gear, hearing aids, and much more.
The Analog ASIC market is huge. (See chart below)
Below is a partial list of the minimum skill sets needed in Analog ASIC design.
Attenuators / VGAs / Filters
Automotive Communication Buses
Camera/Camcorder Analog Front
Capacitance to Digital Converters
Current Sense Amplifiers
Digital Power Management
Direct Digital Synthesis ( DDS) &
Display and Lighting (LED)
Display Driver Electronics
H Bridge & Half H Bridge Drivers
Hi Side & Low Side Drivers
Isolated A/D Converters
Lens Driver Components
Mixers / Multipliers
Modulators / Demodulators
Operational Amplifiers (Op Amps)
PLL Synthesizers / VCOs
Portable Power Solutions
Power Mgmt. (PMIC, LDO,
Power Monitor Drivers
Sample Rate Converters
Sensor Signal Conditioning and
Switched Capacitor Converters
Switches Low RDS (on)
Synchro/Resolver to Digital
Temperature to Digital Converters
Timing ICs & Clocks
Variable Gain Amplifiers
Voltage to Frequency Converters
The medical/industrial world is rife with such requirements yet most ASIC companies are quite unprepared for the challenges of hand-crafting the unique Analog circuitry required for these important applications.
The actual manufacturing cost of the ASIC chip may imply a huge savings when compared to the collective costs of the ICs it replaces. However, there are other costs associated with the ASIC that must be considered and amortized over the life of the product. Non-Recurring Engineering costs, based on the complexity of the design as well as hard tooling costs such as masks and test hardware, can add a few pennies or a few dollars to the ASIC chip cost, depending on the complexity and lifetime volume of the device.
Incorporating elements into the chip that require more exotic processes for features like high voltages / currents or low noise or high frequency can increase the cost of all the elements in that chip. Therefore, it is as important to know what to incorporate into the ASIC as it is to know what should remain a discrete component. Interestingly, the use of multiple smaller, less complicated Analog ASICs, differentiated by their manufacturing processes, can offer surprisingly stunning cost reduction results.
Most Analog applications use a collection of passive elements and discrete transistors in addition to the off the shelf ICs involved. Integrating as many of these passive components as possible to the ASIC often comes for free and can have a dramatic effect in lowering the end product’s total assembly cost as well as size. It is this potential total system cost saving that bolsters the justification to develop the Analog ASIC.
While the term “Mixed-Signal” implies a combination of Analog and Digital circuitry on a single chip, there is a distinct difference in the skill levels required to combine library cells (Analog and Digital) on a silicon chip versus actually creating an Analog design that uniquely satisfies all requirements of the specification. For many applications, Analog library cells offer sufficient performance to meet the system requirements. But more often they don’t. For example, the number of Instrumentation Amplifier cells may be limited to only a few choices, none of which is exactly what the application requires. Even choosing the closest best fit version adds error to the design performance. If several cells are just slightly less capable than what the application needs, these errors can be cumulative and result in the silicon falling well short of its intended performance.
Like the big Analog IC companies, true Analog ASIC companies employ experienced Analog designers who are artisans at Analog invention. Many of them have spent years at the big Analog companies, learning from the industry gurus.
Be careful not to let a Mixed-signal design house negotiate you away from your ideal specification. Close isn’t good enough…analog must be exact.
Perhaps the biggest misconception about Analog ASICs revolves around minimum volume requirements to justify the development and tooling costs associated with putting an ASIC into production. Large standard product Analog IC companies don’t want you to move to an ASIC. They want to keep selling you their expensive off the shelf components so they propagate stories about high tooling costs and high volume requirements.
Moreover, handcrafted Analog can create the differentiation required to break out of the pack with a superior performing chip and thus a superior end product. Additionally, stepping back from the Cell Library approach opens up options for manufacturing, since Cell Libraries are typically developed for one process at one fab. Broader use libraries are available that specify a process, for example, 0.35um CMOS, but have relaxed specifications such that they can be instantiated in multiple fabs.
Handcrafted Analog creates an unlimited set of manufacturing options, especially through the use of boutique foundries. Many of the boutique fabs differentiate themselves by the variety of services they offer and their willingness to make adjustments to their processes to accommodate optimization of the chip’s analog performance
The application will always determine the appropriate combinations of technologies that are best suited for the ASIC design. As our dependence on cognitive prosthesis devices (smart phones, Wii controllers, tablet PCs, IoT, etc.) increases, copper tethers disappear and Analog increases its dominance in ASIC designs. MEMS advances have placed Star Trek style sensors in our daily lives. Medical imaging, sensing and monitoring continues to improve our daily lives. All of these and more increasingly rely upon better, faster, denser Analog circuit content.
When considering a new ASIC design, carefully consider the role Analog will play in its deployment. To minimize risk, choose your ASIC development partner carefully. Most of the time, Mixed-signal ASIC design skills will be sufficient. To minimize risk, seek out an Analog ASIC partner with the right Analog design skills and experience to match the application.
Bob Frostholm, Vice President, Marketing & Sales at JVD Analog ASIC
Semiconductors. (San Jose, CA.)
Email: bob [dot] frostholm [at] jvdinc [dot] com
Bob has held Sales, Marketing and CEO roles at established and startup Analog Semiconductor Companies for more than 45 years. Bob was one of the original marketers behind the ubiquitous 555 timer chip. After 12 years with Signetics-Phillips, Fairchild and National Semiconductor, he co-founded his first startup in 1984, Scottish based Integrated Power, which was sold to Seagate in 1987. He subsequently joined Sprague’s semiconductor operations in Massachusetts and helped orchestrate its sale to Japanese based Sanken Electric, creating what is now known as Allegro Microsystems. In 1999, as vp sales and marketing, he rejuvenated sales revenues and facilitated the sale of SEEQ Technology to LSI Logic. Bob is the author of several technical articles and white papers and in his spare time, an occasional screenplay. Other interests include Home Remodeling, Amateur Radio, Porsche Club Activities and Grandkids. Email: bob [dot] frostholm [at] jvdinc [dot] com