This article describes how to record the AutoTune value on supported Impinj tag chip-based inlays during sensitivity measurements with Voyantic Tagformance. This process is identical for any Impinj tag chip that supports AutoTune, though the AutoTune value location differs by tag chip model.
For tags with AutoTune enabled (default), tag chips fine-tune their front-end impedance by switching between 5 AutoTune capacitance values at every chip power-up and using the best value until the next power-up. Inlay designers may choose to read the AutoTune value during sensitivity measurements in the process of designing new tag antennas.
This article describes how to read a tag's AutoTune values while making tag sensitivity ("Threshold") measurements using Voyantic Tagformance. It assumes the user is familiar with making Voyantic Tagformance Threshold measurements.
The table below shows the associated change in input capacitance for each AutoTune value by Impinj tag chip.
|AutoTune Value||Change in Input Capacitance (fF) by Tag Chip|
|Monza R6||Monza R6-A/B/P||Impinj M730/M750|
- Voyantic Tagformance system with anechoic chamber and antenna
- Tag with Impinj AutoTune (Impinj M730/M750, or Monza R6/R6-P/R6-A/R6-B)
- Voyantic Tagformance software/firmware version 10 or newer
Users can read the AutoTune value at every measurement of tag sensitivity using the Voyantic Tagformance system. On the Threshold measurement screen, navigate to the COMMAND section, change the command from "Query" to "Read" and press "Parameters..." to instruct Tagformance to read the AutoTune values:
Note: to read the AutoTune value for Monza R6, change the WordPtr (hex) to 000E.
After configuring the read parameters and sweep settings, place the inlay in the correct location in the anechoic chamber and click "Start" to begin the measurements. Once the sweep has finished, set the secondary graph to display "Response Data" - this will now show the AutoTune value at every read point.
If users wish to investigate the benefits of AutoTune, they may disable AutoTune by setting the AutoTune disable bit to 1. They may do so by writing 0001h to word 4 for Impinj M730/M750 and Monza R6-A/B/P, or by writing 8000h to word 5 for Impinj Monza R6. They can write the AutoTune value using Tagformance by setting the command to "Write", setting the appropriate write parameters, clicking "Start" to perform a "Write" test in Tagformance, and stopping the test after at least 1 write operation is complete.
For more details on disabling and re-enabling AutoTune with an example using an Impinj reader, see the following article:
With AutoTune disabled, the tag chip will still perform the AutoTune operation to find the best AutoTune value at every power-up, but the tag chip will always use midrange AutoTune value (ATV=2) with no change to input capacitance. The user can still read the AutoTune value even though the chip is ignoring this value.
Performing a read threshold test again will show the results of the tag which now has AutoTune disabled.
With Voyantic Tagformance with Impinj tags, users can measure the change AutoTune makes on input capacitance and evaluate the benefit of AutoTune on improving tag inlay performance.