I’m a Sensitive Chip
Impinj, the largest maker (by volume) of UHF RFID semiconductors, recently announced their next-generation Monza R6 chips. With this chip, Impinj continues their unceasing improvements in RFID performance including a read sensitivity of -22.1 dBm, enabling a 25% greater read range than the existing tag chips, and a tag encoding speed of 1.6 milliseconds for 32 bits. Beyond those performance improvements, Impinj has made a number of other innovations to improve reliability, yields, and performance.
Detecting the Defects
Impinj worked hard on delivering the best quality and consistency from what is really an amazingly inexpensive device. Though defect rates have been quite low, they become noticeable when a retailer is using tens of millions (or in some cases hundreds of millions) of tags every year. To increase the reliability, Impinj introduced what they refer to as “Integra” technology, which is a set of diagnostics that runs on the chip, testing memory and encoding reliability. A brief set of diagnostics is run upon each power-up of the chip, whereas a deeper set of diagnostics can be run on command. These diagnostics enable the chip to self-report failure, rather than relying solely on the testing done by inlay manufacturers and label converters. Not only can those tests miss some defects, but they cannot catch defects that occur later, after the assembly or encoding steps are completed.
Tune In and Don’t Drop Out
Another innovation is AutoTune. Normally tags are designed to work optimally for a specific application on a specific set of materials. If used on different materials, or other products are placed on top of or near the tag, or the moisture content in those materials near the tag increases, then the tag is detuned and performance goes down. Monza R6 has the ability to adjust its own internal impedance to one of five different levels. It very rapidly tries the different levels and selects the optimal one for the current environment. Basically, it re-tunes itself to the current environment and objects it is near. This means the same tag can be used on a wider array of product types1 while lessening the degradation caused by detuning.
The other advantage of AutoTune is that it can adjust itself based on the frequency being used. Normally a so-called ‘broadband’ tag that is designed to work in all of the frequencies around the world compromises some performance to achieve the width of its band. As shown in Figure 1, the red line is a typical broadband tag, which gets less distance than the narrowband tags designed for a specific frequency/region.
Figure 1 – Comparison of Narrow-band vs. Typical Broadband Tag Performance
Impinj’s AutoTune is able to an extent get the best of both worlds. By adjusting the tuning, Monza R6 lifts up the performance at the lower and upper ends, so it can be closer to the ideal performance of the band-specific tag design. This enables a single tag to be used worldwide with better performance than traditional broadband tags.
Figure 2 – Sensitivity (Performance) Improvements Achieved Using AutoTune
Smoothing Out the Bumps = Increased Reliability
Monza R6 also introduced ‘Enduro’ technology to decrease failures and lower the applied tag cost. Traditionally RFID chips have four bumps for attaching the antenna. These bumps stick out and act as stress points that can actually cause cracking of the die (the RFID chip), especially during printing operations where a fair amount of pressure is applied on the tag. A crack may cause the tag to fail immediately and be marked as bad. But worse is when the crack is marginal and the tag tests out OK, but later it starts failing in operation.
Monza R6 addresses this by providing two antenna attachment surfaces that are much larger than the traditional bumps (see Figure 3). This improves yields in part because there are fewer cases of misalignment with the antenna connection leads. But more importantly, this design survives a much greater range of pressures and temperatures without cracking and failing. The most noticeable impact is when the tag goes through the printer, where Impinj said they are seeing big jumps in yields. Impinj is expecting an order-of-magnitude reduction in failures.
Figure 3 – Comparison of Antenna Attachment Areas
Enduro also holds promise to drive down the cost of another component, the anisotropic conductive paste (ACP) used to glue the antenna to the chip. ACP is quite expensive because it contains gold-plated particles. With the big surface areas, tag manufacturers could use less amounts of ACP and yet get a reliable connection with the antenna.
Small is Beautiful
There is a growing demand for smaller form factor tags that perform well, for example, to tag jewelry and cosmetics (two categories the retailers increasingly would like to tag). All else being equal, smaller tags have shorter read distances. To achieve smaller form factor inlays, the inductor loop of the antenna needs to become smaller. To maintain performance, it requires higher input capacitance. But as you raise the input capacitance, variability in the performance of small tags due to detuning effects becomes a limiting factor. With AutoTune, Enduro, and increased chip sensitivity, Impinj has been able to compensate for the detuning effects while increasing the input capacitance to enable smaller tag designs that still perform well. This is what is getting many of their customers excited.
A chip that is more sensitive, more reliable, enables designs to work across a broader range of materials and frequencies, and enables smaller tag designs with good performance – all at the same price point as the previous generation – what’s not to like about Monza R6? The R6 is one more example of why Impinj continues to lead the UHF RFID market.
More reading on RFID: http://www.chainlinkresearch.com/rfid/index.cfm
1 There are limits to the amount of tuning that can be done. You could not design one tag to work well on everything from metals to liquids to fabric — that still requires multiple tag designs. But AutoTune increases the range of types of products and materials that a single tag design will work well on. — Return to article text above
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