Mixed-Signal Integration Empowers Analog Designers to Enter New Roles

The roles of analog designers and power designers have been changing over the past decade. More recently, this trend has been exacerbated by the increasing levels of semiconductor integration and global changes in product manufacturing. In a nutshell, integration is moving upstream from the processor to various analog peripherals, and manufacturing is moving to China. A closer look reveals a very interesting and instructive story.

New Characters

Let’s start by reviewing the evolution of the analog designer’s role. Analog designers (both men and women) were once expected to be masters of an uncanny art of interconnecting more or less single-function devices. Long ago, the devices they dealt with evolved from passives and tubes, then transistors, op amps, and comparators, to simple timing ICs, PLLs, ADCs, and DACs. Their jobs were to drive analog radios and televisions, oscilloscopes and X-ray machines, radar units and bomb sights, most of which interacted with the real world from an analog signal perspective. More recently, the advent of digital outputs has greatly facilitated interaction with microcontrollers or DSPs, and these devices are the domain of the digital designer. (See: An Early Experience with Mixed-Signal Design Disciplines.)

Today, things have changed. When mixed-signal chip vendors release new products, many of them, perhaps most of them, are application-specific and contain the entire signal chain, from collecting analog data in various forms from sensor inputs and turning the analog data into voltage levels to digitizing it through signal conditioning. The output is usually preconfigured for input to one of the chip vendor’s microcontrollers or DSPs. In fact, there are usually complete reference designs available. The only thing the end-product manufacturer has to do is determine what functions to implement, what price point to pay, and the package design to enclose the electronics.

This business model of chip manufacturers seems to be common around the world. Europe, Japan and South Korea are exceptions. IC manufacturers in these regions are large vertically integrated organizations. The main customers of new chips may be internal customers, while the customers of North American chip companies are often Chinese manufacturers.

For analog design engineers, this change in product integration has changed their career prospects. With the exception of engineers working in the industrial control field and engineers in military aviation and telecommunications companies, the design work that used to be done on the bench no longer exists. All the companies I visited agreed that opportunities in the analog design field have moved to chip companies, where analog engineers can be mixed-signal chip designers or application engineers in-house or in the field.

The driving force behind reform

It took some time for things to get to this point. Obviously, the continued shrinking of IC design rules from generation to generation has pushed up integration, but it has also brought various challenges because the allowable operating input voltage has decreased as the physical size has decreased.

Perfecting analog chip design from the analog domain alone would have kept chip production at 0.35 micron. From that point on, it would have been necessary to mitigate basic noise issues through digital techniques.

Indeed, the reduction of design rules has been one of the driving forces behind mixed-signal integration. Connecting signal-conditioning amplifiers to ADCs no longer needs to be left to customer engineers: these engineers are not very familiar with the process technology and the proprietary techniques implemented at each stage of the signal chain. Chip manufacturers must hide the interface inside the chip package if they do not want customers to complain that their products do not meet their data sheet specifications in real designs. Even then, the performance of the final product is unlikely to be improved by the customer modifying the layout developed by the factory. So we found complete reference designs and Gerber diagrams, and found a large number of field application engineers to explain to customers why engineers are really unwilling to use cheap capacitors to save half a penny per circuit board.

OEM or ODM?

The idea that cutting bill of materials costs often kills a design provides the primary rationale for the transition to highly integrated mixed-signal IC products.

This is the dilemma facing companies (OEMs and ODMs) that buy new mixed-signal products and turn them into consumer products for the general public and the emerging middle class.

Let's first understand the acronyms - OEM is short for Original Equipment Manufacturer, and ODM is short for Original Design Manufacturer. I couldn't find a clear explanation on the web that I agreed with, so I'll come up with a definition that is consistent with what I've heard in the chip business.

In a nutshell, it's a hierarchical situation: OEMs make branded products for companies that sell branded products. ODMs make components, which may be slapped with GUIs by multiple companies, packaged in cases, and sold under multiple unregistered trademarks.

The name OEM is an extension of the OEM concept in the automotive business. A windshield wiper motor that Ford or Toyota sells to the average consumer may be made by an outside manufacturer to Ford or Toyota's specifications. The motor may also require some kind of acceptance before it enters Ford's or Toyota's "factory to dealer" supply chain. The Ford or Toyota brand and the fact that the motor comes from the parts department of the car company give us confidence that we are willing to pay a higher price for these products than for products with the same specifications purchased from the catalog.

In the case of electronics produced by Chinese manufacturers (which may have purchased the brand rights to a previously well-known North American brand), the operating mechanism is similar: the product sold under the name of the brand-owning company is unmatched, and the company may have worked for a decade or more to build its reputation through superior performance, quality, and customer support.

In China, such companies tend to target overseas markets. That’s not so great when overseas markets are bad, as they are now, and it can’t support the typically short life cycles of consumer products. (We’re supposed to buy a new TV every three years.)

At the same time, the size of China's middle class is growing day by day; this group of people may be larger than the middle class in any other region of the world. These ordinary people generally do not use first-class consumer products, so they now have a strong desire to buy.

It is also important to remember that they don't have credit cards, so while they can't spend as much as Western consumers, they are unlikely to cause a bubble, which is probably a good thing if, like China, you have been taught strict Marxist economics.

This is the situation that OEMs face. If the chip company's reference design has enough features to support a common design at a variety of price points (proportional to the number of features implemented), if the design can be offered in different configurations through multiple domestic brands, and the ODM can quickly bring it into production with minimal non-recurring engineering (NRE) costs, then this product is a successful product.

It can also be said that a product is successful if it supports the end user's expectations of price and performance. For example, a long time ago, I wrote an article about the Japanese and Chinese air conditioner markets (http://electronicdesign.com/article/power/air-conditioner-chip-set-is-way-cool12211.aspx). The issue was the motor control required for different compressors and the trade-off between price and quietness. Japanese consumers are willing to pay a higher price for a quieter air conditioner; Chinese consumers only require that the air conditioner can cool.

Besides economics, there are all sorts of other cultural considerations. If you live in a country where there is a severe shortage of doctors and hospitals in much of the country, then relatively inexpensive medical equipment used by relatively unqualified doctors will make a huge difference in overall health care. Thus, you'll find ODMs producing not only cheap laptops, air conditioners, and cameras, but also basic ultrasound machines. (See: An Early Experience with Mixed-Signal Design Disciplines, http://electronicdesign.com/article/analog-and-mixed-signal/New-Technology-Treats-Medical-Needs-In-Developing-Countries.aspx.)

The OEM or ODM business model does not work if it requires the vendor to deal with high NRE charges. This is another factor that supports semiconductor vendors focusing on the more difficult analog design work, rather than following the old model of developing a variety of individual high-performance ICs and "throwing them at" the end product designer.

Lack of mentors

Avoiding this disconnect is also an aspect of modern China's development. Whenever I talk to senior engineers at semiconductor companies about which group the future analog designers will come from, they always tell me that new college graduates need at least five years of guidance from senior designers before they can really play a full role.

There is no doubt that young students studying in China's engineering design schools are both smart and hardworking, but after graduation, they face a serious shortage of senior mentors. It is reported that this problem has been alleviated to a certain extent due to the return of retired engineers who have worked overseas for decades, but this problem will not be completely solved until more fresh graduates have matured.

This doesn’t mean that young Chinese engineers are standing still. Multiple sources show that young Chinese engineers rely heavily on their own social media to seek mutual support on technical issues.

Impact extends to fabless

So far, the scope of this article has involved traditional semiconductor companies and their customers, but the trend toward high levels of mixed-signal integration and complete productization through reference designs also extends to fabless startups. As an example, I previously wrote about Samplify, which evolved from an IP provider to an ADC provider to a complete product design provider for portable ultrasound devices (http://electronicdesign.com/article/analog-and-mixed-signal/The-Mind-Of-An-Entrepreneur.aspx).

Samplify's path to making the leap is by optimizing for ODMs, but it's not the only way fabless companies can go. Scottish company Wolfson Microelectronics says it is looking to get its codecs into reference design boards for large companies, which can then sell their products to OEMs.

Outside China

It’s hard to discuss this trend without talking about the Far East in detail, given its influential consumer product output, but higher levels of integration and pre-optimized designs are also beginning to emerge in the Western industrial control market.

Industrial control is, by definition, a regional field focused on a specific industry, and any one project in the industrial control field requires very few ICs compared to consumer products. Still, the industrial control field is big business for distributors in general. The problem here is that as semiconductor companies continue to recruit more and more recent college graduates and send them to work as chip design engineers and application engineers, there is a certain shortage of new analog design engineers (both large and small design companies) to work on industrial control development. At the same time, senior design engineers are getting older and retiring, which on the one hand causes a loss in experience, and on the other hand exacerbates the situation of reduced supply.

Recognizing this, some semiconductor companies are beginning to change. National Semiconductor (NSC) is a good example. One of the factors that will surely bring NSC back to life after being acquired by Texas Instruments (TI) is its portfolio of WEBENCH online design tools. Historically, these products have focused on designing with relatively simple ICs (compared to the ICs discussed in this article), but this has changed with the recent release of signal conditioning products customized for specific sensors. Complementing the new hardware is a new WEBENCH implementation that customizes the entire signal chain. (See: Chips Implement Sensor Signal Chains From Nanoamps To Bits at http://electronicdesign.com/article/analog-and-mixed-signal/Chips-Implement-Sensor-Signal-Chains-From-Nanoamps-To-Bits.aspx).

An example of such a sensor product is the LMP91000, a programmable analog front end (AFE) for electrochemical sensing applications, which can be found at http://www.national.com/pf/LM/LMP91000.html#Overview.

Power Factor

Since the advent of digital control in switching regulators, power management IC vendors have followed a similar path to mixed-signal IC vendors. This is especially true for applications using intermediate bus architectures (IBAs), where closing the control loop in the analog domain is often viewed as an analog magic trick. As a result, chip vendors such as Power-One and NSC support their "digital" power products with graphical user interfaces (GUIs), which take all the design work and much of the analysis work out of the bench during the design process.

For the most part, these products are DC-DC switching regulators, but Vicor recently released a power design tool called PowerBench that supports designs ranging from simple buck and boost regulators to complete multi-output AC-DC power supplies.

Mixed Signal Product Examples

Next, we will take a look at recent product releases from various semiconductor companies to illustrate the various mixed-signal chips mentioned above.

Last March, TI released 16-bit and 14-bit dual-channel simultaneous sampling successive approximation (SAR) ADCs, both of which come with independently controlled internal voltage references to simplify system-level design. The 16-bit ADS8363, 14-bit ADS7263, and 12-bit ADS7223 (Figure 1) can provide twice the throughput per channel of similar ADCs, supporting sampling rates up to 1Megasample/s. The target applications of these ADCs are industrial control, not consumer or medical applications. Typical applications include motor control, power quality measurement, power automation, and solar and wind power inverters.

Figure 1: Bulletproof's reference designs are essential to selling and applying ICs that are designed to remove the hardware needed to design specific mixed-signal applications. This board for Texas Instruments' ADSxx63 dual-channel SAR for industrial controls is fairly simple because the chip is relatively simple to use.

The integration of two independently controlled 2.5V voltage references allows for independent ADC gain calibration and implementation of programmable gain amplifiers. In addition, this capability reduces the need for external signal conditioning when each ADC requires a different gain level.

New products from Linear Technology are generally targeted at automotive applications. From a high-integration perspective, Linear Technology's LTC6803 second-generation high-voltage battery monitor for hybrid/electric vehicles (EVs) and other high-voltage high-performance battery systems can solve the problem of high voltage through a series battery pack. Multiple LTC6803s can be connected in series without the use of optocouplers or isolators (Figure 2), allowing accurate voltage monitoring of each battery in the battery array. Each LTC6803 battery measurement IC contains a 12-bit ADC, a precision voltage reference, a high-voltage input multiplexer, and a serial interface. A single LTC6803 can measure up to 12 individual batteries in series. The battery voltage range that can be measured is -300mV to 5V, which enables the LTC6803 to monitor many different chemical batteries and supercapacitors. In addition to precision measurements, each cell can be monitored for undervoltage and overvoltage conditions, and an associated MOSFET is provided to discharge overcharged cells. There is also a 5V regulator, a temperature sensor, GPIO lines, and thermistor inputs.

Figure 2: Linear Technology's highly integrated roadmap for niche markets includes many technologies for monitoring the status of electric vehicle battery packs without optocouplers.

Measuring an automotive battery array presents some unique requirements, leading to some equally unique solutions. For example, for long-term battery pack storage, the current consumed by the integrated battery management system can cause the cells to become unbalanced. Linear Technology's response is a standby mode in which less than 12 microamps are drawn. In addition, because the LTC6803's power input is isolated from the battery pack, the LTC6803 can draw current from an independent power source, in which case less than 1 microamp will be drawn from the battery pack. On top of this, the chip must also meet automotive temperature, environmental, and safety standards.

In January, ADI released the first product in a family of analog front-end chips for electrocardiogram (ECG) systems, which measure and record the electrical activity of the human heart (Figure 3) to diagnose and analyze conditions such as birth defects, arrhythmias, heart valve problems, and insufficient blood flow to the heart muscle.

Figure 3: Analog Devices’ analog front end for portable ECGs saves power and BOM cost while meeting stringent requirements.

The ADAS1000 ECG AFE can eliminate more than 50 components in the signal chain of a 5-electrode ECG monitoring system. The device also integrates pacemaker pulse detection and respiration measurement functions. This is a versatile device because it can be configured to optimize noise performance, power consumption, or data rate. These indicators are different design goals for home, outpatient, and hospital ECG systems.

For ODMs and OEMs, there is naturally quite a bit of design support. The evaluation board includes the analog front end, power, control, and interface options. Since the analog front end is unique, ADI integrates it with ADI's Blackfin DSP (digital signal processor), single-chip USB isolators, four-channel digital isolators, 5kV DC-DC converters, 433MHz, 868MHz, and 915MHz ISM band transceivers, and a variety of DC-DC regulators.

TI has also introduced a family of analog front ends for portable ECG systems. The latest 24-bit ADS1298R integrates respiration detection functions and integrates more than 40 discrete components (so many components would be needed if they were not integrated). The power consumption of this chip (Figure 4) is 95% lower than that of discrete implementations. On-chip devices include eight ADCs, eight programmable gain amplifiers (PGAs), eight active filters, as well as a pacemaker detection interface, continuous disconnection detection function, a voltage reference, and right leg drive circuit. In the reference design, the chip is used in conjunction with an ultra-low-power DSP. The reference design can also implement oscilloscope, FFT and histogram displays, which reflects the design support provided by chip companies in these targeted mixed-signal chips.

Figure 4: Companies other than chip makers will benefit from the trends described in this article. TI's ECG products are comparable to those of ADI. The evaluation board can be used with this commercial simulator from Fluke.

Integration sometimes involves MEMS. In January, ADI launched the high-performance MEMS microphone ADMP441 with I2S (Inter-IC Sound, audio chip interconnection) digital output. (This is a pre-production announcement, and mass production will begin in June this year). The company has previously launched other microphone products in its iMEMS series, but this new microphone device does not require signal conditioning and digital operations, but directly provides 24-bit serial data output. Its specifications are as follows: frequency response is 100Hz to 15kHz, SNR is 61dBA, and power supply rejection ratio (PSRR) is 80dBFS. It uses a 4.72×3.76×1.00mm3 package.

Figure 5: Integration does not mean the absence of electronics. ADI has integrated the MEMS microphone with its associated electronics to create a rugged device in an extremely small form factor.