Better than Reference Design…on the first board spin
The design and layout of the printed circuit board (PCB) for a wireless product is crucial to its ultimate performance. With the ever increasing demand for higher levels of integration, PCB design is something that cannot allow for short cuts to be taken. It is not a stretch to say that the PCB is the functional foundation within a wireless product. Cutting corners on this critical component is something that will result in program delays, returned products, and increased costs. While everyone understands the downside of cutting corners, it is amazing how often it is done. It can be attributed to old habits, not understanding the benefits of new technology, or simply looking for short term gain in light of significant risk of long term loss. OneOak Design, Inc recently worked to help a client break free of some old habits and achieve better performance than the reference design on the first board spin. What is the secret? OneOak applied good design practices in combination with proper use of any layer via PCB technology in order to provide performance results far beyond expectations.
The level of integration in a mobile phone is astounding when you step back and think about it – WAN, Bluetooth, WiFi, UMTS, GPS, camera, and all the typical mobile storage interfaces as well. You cannot take the integration of all these competing technologies in an enclosure that fits in the palm of your hand lightly. Communication amongst team members is key to adopting a flexible, front-loaded design approach. A good analogy is to think of the program like dominos. The designers need to set them up properly and effectively in order to knock them down and have everything work as planned.
The first task OneOak set out to work on was the plan for circuit schematic and board-level shielding design. The high level design progressed as most programs do – there are always some issues to work out, but the reference design mostly mapped the way. The biggest hurdle facing this program was that the team had to produce a PCB that was less than half of the square area that was achieved based on the form factor compliant reference design. The concept of improving on the reference design is not new. Every new product wants to push the limits and do better than the company before them, but a 50% reduction in size requires the typical design and engineering practices to be challenged.
Simply fitting all the required components into an envelope as small as desired by the marketing team was a challenge. Once it was determined that the parts could even fit, figuring out how to connect the components within the PCB needed to be tackled. In order to achieve the goals for this program, something other than standard High Density Interconnect (HDI) layout practices was required. Based on One Oak’s past experience and some educating of our client, it was agreed that the program was going to require the use of an Any Layer Via technology. There are several companies that provide competitive any layer via solutions, but the one chosen for this program was ALIVHTM from Panasonic. It has been our experience that Panasonic’s ALIVH provides a proven technology that allows for the ability to achieve the level of integration required for a handheld wireless device. In the case of this product, ALIVH provided several solutions to issues that were critical to the success of this program:
- Signal Integrity – Enabling multiple high speed interfaces and technologies to co-exist without negatively influencing each other
- Layout Efficiency – Fitting all the components of a wireless phone onto real estate smaller than the size of a credit card means components must be placed more aggressively than traditional layout techniques can allow.
- Flexibility of component placement – getting all the chips and connectors to fit and work within the scope of the whole project is difficult in the best of times.The ALIVH technology allowed for leeway on issues like button and connector placement.
During the planning phase, iterations between the team disciplines occurred to overcome several design challenges and achieve the desired product requirements. OneOak worked hard to ensure that the best solution for all was achieved. Fractions of a millimeter were often discussed. A team that understands how a millimeter can drastically change the outcome of a wireless product on several technical levels is critical to a program. The location of a button can affect the user’s overall satisfaction with the product as much as not having enough RAM to allow it to effectively function, or poor reception due to compromises on the antenna design dictated by the Industrial Design. Changes late in the development cycle are what will ultimately prematurely end a program. OneOak worked hard to achieve an overall product design that was locked down before any effort in the circuit layout of the product had started.
When a Plan Comes Together
With the planning stage complete the program continued to the realization of the product. Working with the Mechanical Designers, our Electronic Designers established an outline for the PCB and began the component layout. The choice of using ALIVH was one that contributed heavily to the success of this program. ALIVH provided the ability to tightly pack components on the board as well as to utilize several layers of the board for isolation and shielding of different systems. This flexibility and layout control is something that would not have made the ambitious size requirements for this product achievable otherwise. It was OneOak Design’s experience working with the Any Layer Via technology that gave the client a solution that would not have occurred without previous experience working with this technology.
The design progressed with very few issues allowing the product to prepare for prototyping. Housings and PCBs were assembled for the first time. Smoke tests were performed on the circuit board and software was installed on the boards to get that first glimpse into what the final product was going to look like. With the core design looking to be complete, the product was ready for its big debut at one of the large wireless industry trade shows. What the team didn’t realize yet was the depth of the success. The following functional test results provide insight into how successful the design choices had been.
This program required testing on 5 separate wide-area network (WAN) standards including three 2 G standards (GSM, GPRS, and EGPRS) and two 3G standards (WCDMA and HSDPA) along with WiFi and Bluetooth.
The following charts will show performance data of our two test subjects:
1. Manufacturer’s reference design platform
2. OneOak’s design based on the same reference design.
Figure 1) Receiver (Rx) sensitivity of the Reference Platform (left) vs. OneOak’s Layout (right)
In figure 1, conducted receiver sensitivity measurements were performed with the devices operating in the GSM850 band operating in GSM/ GPRS mode(s). From the results, we can see that the overall sensitivity of the OneOak device is at least 5dB (3x) better than the manufacturer’s reference design platform. This improvement translates into better range, higher throughput, and possibly improved battery life.
It should be noted that initial tests were not performed in a shielded environment which is demonstrated by the interference ‘spikes’ seen at the low end of the band. This interference does not degrade performance mid to high band (interference shown in the Reference Platform’s graph is caused by nearby base stations in the area).
The following charts the transmit performance between these two devices:
Figure 2) Transmit (Tx) Power Levels of the Reference Platform (left) vs. OneOak (right)
Figure 3) Tx Frequency Error for Reference Platform (left) and OneOak (right)
As seen above, the OneOak design falls within the standards mask for transmit output power levels coinciding from the data gathered from the reference platform. Also note an improvement in transmit frequency stability as shown in Figure 3.
The following graphic shows the performance at higher frequencies in different operating mode(s).
Figure 4) Rx sensitivity and Tx Power Level of OneOak device
Figure 5) WCDMA Rx sensitivity and Tx Power performance of OneOak device
The final set of data shifts our focus to the one element that can cause the biggest challenge for high speed, highly integrated designs: meeting regulatory emissions standards. The graphs show that, with a minimum of 5dB of margin, this device can be submitted for formal Regulatory testing and meet the standards outlined in the graphs above.
Figure 6) Receiver Radiated Emissions, WiFi On, Bluetooth Off, USB Connected to Laptop
Figure 7) Radiated Emissions, WiFi Off, Bluetooth On, USB Connected to Laptop
In the End…..
What has been achieved on this program is simple in principle but difficult in practice. Building and working within a team that understands the needs of all development disciplines involved was key to the success of this program. The data shown in this document shows how OneOak Design worked using proper practice, technique, and technology to provide the client with a product that laid the foundation for success on the first board spin. What this translates to is significant savings in both bottom line budget costs and program timeline. An outcome every program manager hopes to achieve.
OneOak Design, Inc. is a product design and engineering company based in the Vancouver, BC area. OneOak Design brings to the table a thorough understanding of the pain required to bring a product to realization. This understanding translates to a better product and long term profitability that can be lost through typical cost cutting measures found in many product development cycles.
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