10 Embedded Design Trends

Bluetooth, FreeRTOS, and multiprocressing are all on the rise in embedded systems, according to latest annual survey, released in at EE times!  FPGAs, 8-bit microcontrollers, and in-house custom operating systems are on the decline.

The following pages give a few snapshots of those and other top 10 trends in embedded systems designs.

The annual study takes a broad look at market and tech trends in embedded systems design. A total of 2,258 engineers responded to the latest survey, conducted online Jan. 18 to Feb. 21, giving a 2% confidence level for most questions.

Most respondents (55%) were from North America, with 22% in Europe and 14% in Asia. They came from a wide range of sectors including industrial (33%), consumer electronics (24%), communications (22%), automotive (18%), and medical (18%), among many others.

 

WiFi rules, but here comes Bluetooth

WiFi is twice as popular as the second most used wireless transport. But Bluetooth is catching up fast, particularly the 4.0/LE/Smart version. Surprisingly, cellular seems to be declining. Meanwhile, proprietary interfaces are declining, and 6WLoPan is not gaining traction yet.

 

 

Open-source takes over

For the first time in the survey's history, open-source operating systems outpaced commercial OSs. Use of open-source code now runs in 36% of systems, compared to 33% for commercial OSs.

 

 

Android, FreeRTOS lead the way

Asked to select all the open-source OSs they use, engineers said Android and FreeRTOS are their top choices. They are poised to exceed the in-house/custom OSs that have dominated use for years but have been in decline.

 

 

Show me the source

The most important factor in choosing an OS is availability of full source-code. According to our survey, engineers really want to fiddle with the bits. Of course, some tech support and no royalties are cool, too.

 

 

Multiprocessing goes mainstream

For the first time, half of survey respondents said they use more than one microprocessor in their current designs. In fact, the average number of micros is 2.4.

 

 

32-bit in, 8-bit out

Surveys have shown a slow but steady decline in use of 8-bit microcontrollers and a similar rise in 32-bits. The trend continues in 2014 when we asked about what MCU is used in your current design.

 

 

FPGAs trending down

FPGA use is trending steadily down from 45% six years ago (not shown) to 31% last year, rising very slightly this year to 32%. Stay tuned to see whether we have we hit the bottom or the decline continues.

 

 

Virtual doldrums in embedded

We started asking about use of virtualization in 2013 and found out it is pretty low among embedded systems designers. It dipped slightly in the latest designs, but we expect it eventually will gain traction

 

 

 

IoT on the map

Industrial controls has been the leading application among respondents for many years. This year the Internet of Things made a first, strong appearance on the list. Communications and computers are both trending down. Consumer electronics, automotive, medical, and electronic instruments all trend up.

 

 

Skeds are slipping

As we reported in March at EE Live!, respondents said their embedded design teams are getting a little smaller and slipping schedules more often. In 2014, 41% of all projects finished on schedule or ahead of schedule, and 59% finished late or were canceled.

LISA LIU
lisa@jaapson-pcb.com
www.jaapsonpcb.com
skype: jaapsoncircuits
Jaapson, HDI multi-layer PCB manufacturing for 10 years

 

What Determines Impedance Control?

For standard circuit boards, a PCB manufacturer is given a set of patterns - copper patterns, hole patterns, ink patterns, which are combined into a single circuit board with all the pattern sizes and positions within certain tolerances. Failure to meet a certain size or position with the specified tolerance can be cause for the circuit board to be rejected. If a trace has been defined as an impedance control trace, it is not the trace size which is strictly defined, but rather the impedance. While a nominal trace size will be provided in the Gerber layer, it is understood the circuit board manufacturer can vary trace width, height, and dielectric thickness as long as the final impedance is within tolerance.

 

Generally speaking, 3 levels of service are available for an impedance control printed circuit board.

 

No impedance control. 

The impedance tolerance is loose enough that simply making a design with no extra precautions will result in the correct impedance as long as the design is made correctly within the standard specifications. This is the fastest and least expensive option since it places no extra burden on the circuit board manufacturer.

 

Impedance watching. 

The designer indicates the impedance control trace. The PCB provider adjusts the (W)width of the trace and (H)height of the dielectric and gets approval on the proposed specifications before starting manufacturing. A TDR (Time Domain Reflectometry) test can be performed to confirm the impedance for an additional cost.

 

Impedance control. 

Usually reserved for high-end designs containing either an odd design that doesn't fit the usual microstrip configuration or a tight tolerance. With manufacturing capability limits approaching the dimension requirements, confidence is not high the target impedance will be achieved on the first pass. The circuit board manufacturer first makes the board, getting as close to the target impedance as possible. Next a TDR test is done to determine if the impedance is within specification and adjustments are made as necessary. In the example below, the prepreg (composite fibers "pre-impregnated" with an epoxy) can be added or removed in 1 mil increments to affect H, and changes can also be made to W. Multiple iterations may be needed depending on the design.

 

 

At higher frequencies, the impedance will depend on the geometry of the circuit so it has to be calculated. These calculation are complex. 

 

In the case of a microstrip, the impedance will depend on 4 parameters :

 

H is the height of the dielectric. It can be changed in steps. In this example +/- 1 mil results in +/- 2 ohms

Er is the dielectric of the material. It is fixed once the material is chosen. Having a good idea of the Er is necessary since +/- 0.1 results in +/- 0.5 Ohms. To make things more complicated, only certain specialty materials like Rogers 4003 have well-defined dielectrics.

T is the trace thickness. An outer trace is plated, providing a 20% uncertainty in exterior traces. This results in a small uncertainty of +/-0.2 ohms.

W is the trace width. Typical trace width uncertainty is +/-2 mil which results in an uncertainty of +/- 2 ohms.

 

In the example provided, if the target impedance is 50 ohm, a 26 mil trace width is required. Since there is a tolerance on the input parameters it translates into a tolerance on the trace width. Achieving the calculated trace size should result in the required impedance.

 

A typical tolerance on final impedance is +/- 10%.

 

Achieving this requires a good understanding of the Er values and experience about how dielectric laminates behave. Ensure your PCB manufacturer has the knowledge and capabilities to meet your requirements. Specifying impedance control ensures you will need to work closer with your circuit board provider but the results are worth it.

 

 

 

Baggio WANG
baggio@jaapson-pcb.com 
www.jaapsonpcb.com
skype: baggiowang0214
JAAPSON, Expert in HDI Multi-layer PCB manufacturing