TMS3705: RF Amplifier Spice Model

Hello Jim,

a Spice model for the RF amplifier can not be provided.

Please have a look to the following thread which may also contain some useful information for you:

https://e2e.ti.com/support/wireless-connectivity/other-wireless/f/other-wireless-technologies-forum/692240/tms3705-methods-to-increase-the-read-range-of-the-receiver

Best Regards,

Helfried

Hi Helfried,

Thanks for the thread. The TRF4140-Q1 might be an option to explore. 

We have had a different experience to the one that the expert on the TMS3705 has mentioned. The RFID tag will receive energy and transmit but the received data is not processed properly after the RFID tag is a certain distance from the antenna. So, we have an energized and transmitting tag but failed tag identification. We monitor the tag by wrapping a coil of wire around the plastic housing that the tag is mounted in. We can see on the oscilloscope the exact charge time and transmit time for the tag and can confirm that the tag is transmitting but at that same time the ID data is not captured properly until we bring the tag closer to the antenna.

There can be, and likely are, more issues regarding receive sensitivity including system noise and how well the TMS3705 supply voltage noise is being suppressed. We are currently looking at revising our power regulator to a low noise LDO linear from the previous switching regulator.

So far our testing results are showing that the Rx sensitivity is the most likely area to focus on. 

Best regards,

Jim  

Hello Jim,

to check the power supply in this case is a good idea. We also noticed problems with switching power supplies in the past.

The measurement you do is just the same as we do to check when the transponder starts to shorten the response du to the lack of energy. But as long as the transponders sends the full response the reader should be able to receive this signal.

Best Regards,

Helfried

Hello Helfried, 

Something that came to mind is the Q of the antenna and the difference in signal level for 124kHz and 134kHz. I think in most cases the antennas are tuned to resonate at 134kHz and the transmitter frequency is the same. However, when the transponder begins to transmit a half-duplex FSK signal, the 124kHz frequency at the receive antenna is off peak. If the antenna Q is quite high, the difference in signal levels at 124kHz and 134kHz will be very different and may cause some issues during the TMS3705 read phase. I know the TMS3705 has significant gain with a limiting amplifier stage which will help level off the difference but there still is a possibility that a read problem may arise. 

Also, can you confirm my understanding of the transponder transmit power versus charge time. I understand that once the transponder receives sufficient energy it begins to detect when the transmit charge signal stops and then the transponder begins to send the data bits to the TMS3705. The transmit power from the transponder is capped or limited no matter how long the charge time signal happens to be. So even if the charge time doubled, this would not give the transponder more transmit power and no further transmit range would be realized. Is this correct?

Best regards,

Jim