Design Talk: Prototyping and Design
There are always things to consider when prototyping a design. Here are a few essays on the subject to aid you in your efforts.
Designing a Medical RFID Asset Tag to Withstand Sterilization Cycles
Collaboration between OEM and battery manufacturer leads to product Innovation
By: Sol Jacobs, Tadiran Batteries, www.tadiranbat.com
A technology-driven world presents a growing number of opportunities for wireless, battery powered radio frequency identification (RFID) real time location systems (RTLS) that support enhanced data capture and seamless information management.
While these battery-powered systems have become ubiquitous in manufacturing and distribution applications, this technology is also gaining traction in many wireless applications, especially those involving extreme environmental conditions. For example, high temperature lithium thionyl chloride batteries have been used for decades to power EZ-Pass automotive toll tags, providing a proven track record for reliable performance in withstanding the extreme temperatures associated with automotive windshields. More recently, the same concept has been applied by Awarepoint Corporation for use in the first active RFID asset tags capable of withstanding the high temperatures associated with equipment sterilization cycles.
Driven largely by regulatory compliance requirements and legal liability concerns, hospitals and other healthcare facilities are quickly embracing active RFID asset tracking to save time and money while improving data capture and reporting capabilities. Active RFID systems are ideal for monitoring the location of portable medical equipment such as wheelchairs, gurneys, IV pumps and pulse oximeters. RFID asset tags are also being utilized to monitor the physical movements of patients and provide instant access to key patient information. Active RFID systems can also be used to monitor the activities of attending doctors, as well as to provide precise record surgical and therapeutic procedures, diagnostic tests, and the dispensing of pharmaceutical drugs and medications.
Since many of these applications require autoclave or chemical sterilization cycles at temperatures as high as 135°C, Awarepoint Corporation (www.awarepoint.com) employed high temperature lithium batteries when it designed the Awarepoint T2S, a self-contained, battery-operated active RFID asset tag.
Following data drawn from customer surveys, Awarepoint identified the inability of standard battery packs to withstand extreme temperatures as a hot button problem. Earlier generations of active RFID asset tags used batteries that were not designed to withstand the temperatures associated with autoclave and chemical sterilization systems. As a result, certain medical equipment that requires autoclave or chemical sterilization could not be tracked using traditional real-time location solutions (RTLS). This increased labor costs and defeated the full-value proposition of using RTLS technology to provide fully automated and verifiable real-time 24-hour monitoring and reporting capabilities.
After thoroughly reviewing all available battery technologies, design engineers at Awarepoint chose TLH-2450 coin-size lithium thionyl chloride batteries from Tadiran as the primary power for the Awarepoint T2S asset tag. The upgrade paid off, as environmental tests showed that the TLH-2450 cell could withstand 135°C temperatures associated with standard autoclave cycles, and could work continuously for 500 steam sterilization cycles on the original battery to reduce maintenance costs. These compact, weight-saving (8.8 g), 3.6 V cells feature 0.55Ah capacity @ 0.5mA, and a maximum service life of up to 20 years. TLH-2450 cells are also completely safe, U.L. recognized, and considered non-hazardous when shipped. Other high temperature lithium cells are available in coin-size, as well as cylindrical batteries ranging in size from ½ AA to DD. Custom battery packs are available as well.
Use of the TLH-2450 battery pack also enabled a simple retrofit with no injection molding die retooling required. Also, since Awarepoint T2S asset tags can be sterilized while remaining attached to the medical device, hospital staff are now able to locate a device in the sterile processing department and determine its clean/dirty status with the click of a button, eliminating time consuming and frustrating searches for equipment throughout the hospital’s sterile processing department. Further, alerting capabilities within Awarepoint’s Securpoint application allow hospital staff to program T2S asset tags to alert medical staff if a device is returned to service without proper sterilization.
The development of the Awarepoint T2S active RFID asset tag demonstrates how design engineers need to solve design challenges by truly understanding the needs of their customers, then work with a battery manufacturer to apply an intelligent power management solution capable of raising the bar to higher performance standards.
High Bandwidth Data Interfaces Growth
With the growing demand for advanced multimedia capabilities, higher resolution displays, and camera modules, system characteristics of the cell phone application have evolved tremendously over the past few years. A consequence of this growth is the significant increase in signal speed and number of lines between the host processor, the display subsystem, and the imager to transfer media-rich content. As a result, for handset designers who are worried about maintaining good signal integrity, finding a solution for electromagnetic interference (EMI) filtering with low channel capacitance and robust electrostatic discharge (ESD) protection is a critically important concern.
In handsets with clamshell or slider configurations, a flexible cable connects the main system board to the liquid crystal display (LCD) module. When signals are transmitted through the flexible cable at high frequency, the cable behaves as an antenna and radiates EMI to the external environment. Therefore, high performance EMI filters, combined with a high level of ESD protection are required to suppress radiated frequencies and preserve the best signal integrity possible on high speed signals.
The industry has reached the point where traditional architectures, based upon resistor - capacitor (RC) pi filters, impose limitations in terms of signal integrity and system robustness, and advanced integrated passive solutions based on a new architecture are required.
Important Considerations when Selecting an EMI filter
When selecting an optimal EMI filter for wireless handset applications, designers should consider multiple factors to ensure superior filter performance and robust ESD protection while maintaining excellent signal integrity. These factors include:
Limitations of Traditional Architectures
Pi filters based upon a RC architecture have been the most popular for addressing EMI issues in wireless handsets. As handsets handle increased amounts of data transferred at higher speeds, higher cutoff frequencies are required to preserve excellent levels of signal integrity. However, the requirement to deliver the greatest level of attenuation at critical carrier frequencies (800MHz to 2.5GHz) remains unchanged.
To increase cutoff frequency using RC-based filters, filter designers have focused on reducing capacitance levels on the line. Unfortunately, this results in significant degradation of the attenuation levels at carrier frequencies. With key attenuation requirements no longer met, increasing the cutoff frequency of an RC EMI filter by decreasing the capacitance value is not a viable option.
Another unfortunate limitation of the RC architecture is the insertion loss in the pass band, traditionally around -6dB, which contributes to the degradation of the signal-to-noise ratio. Also, some existing solutions in the market do not integrate a high level of ESD protection, which is required to optimize the robustness of the system on the flex cable.
A New Solution: California Micro Devices Praetorian III Architecture
To bypass these limitations and address emerging requirements, California Micro Devices has developed breakthrough Praetorian (add registered trademark symbol) III architecture. This architecture enables the integration of spiral inductors with other passive components and ESD protection diodes on a single chip.
This enhanced EMI filter architecture address the emerging problems facing wireless handset designers and allows optimization of signal integrity on all interfaces in the wireless handset application: display and camera interface, audio interfaces, USB ports and all interfaces highly sensitive to the quality of the signal. This new architecture raises the bar in terms of performance, form factor and cost.
Praetorian III Architecture Benefits
The Praetorian III architecture utilizes a six pole pi-filter topology and features high cutoff frequencies, high levels of attenuation and robust ESD protection up to 15kV contact discharge consistent with the IEC 61000-4-2 level 2 standard. Taking advantage of higher value inductors in the available chip area, it allows the use of smaller value capacitors resulting in a filter design with input capacitance as low as 10pF, significantly enhancing signal integrity. The coupled inductor’s compact size also allows the design of filters that can fit into small form factor.
Because Inductor based EMI suppression solutions offer a much steeper attenuation slope and these steeper slopes create a more stable attenuation mask over device operating voltages, it is now possible to achieve attenuation masks ranging from 700MHz- 6000 MHz with 400 MHz cutoff frequencies.
Using this innovative inductor based EMI suppression for high speed parallel interfaces, Praetorian III architecture enables a reduction in total capacitance, provides best in class attenuation, and up to 15 kV contact ESD protection. Features include:
Lower filter capacitance permits faster clock speeds and higher cutoff frequencies and provide the following support:
The following table summarizes the applications where Praetorian architecture becomes necessary to optimize signal integrity with sharp rise times and to avoid significant applications issues.
Praetorian III Application Benefits
Finding a filtering solution with low channel capacitance is a critically important concern to handset design engineers who are worried about maintaining signal integrity. The Praetorian III architecture allows for higher cutoff frequencies and better signal integrity, stop band attenuation at lower frequencies, and true ESD protection that will not degrade over time