Other Parts Discussed in Thread: TXU0102
Hi Team,
This issue is an extension of a previous matter regarding read range for a RO Transponder and a TMS3705E. A new design was created that uses the TMS3705E along with the UCC27424DGN driver chip to increase the drive voltage and energy supplied to the antenna. The UCC27424DGN drives a differential passive circuit that allows the antenna resonance to be adjusted to 134kHz with selected capacitors. This circuit provides greater signal swing at the antenna with reasonable supply voltage (<9vdc) on the UCC27424DGN. The additional benefit of this design is that the antenna common mode is at DC ground to provide safer operation.
The read path is also differential from the antenna resonance circuit and is filtered (bandpass) and amplified by a differential to single-ended amplifier with gain selection greater than 100 (currently). The single-ended receive signal is AC coupled to the TMS3705E. An additional 1k ohm shunt resistor was added just before the 47k series resistor connected to pin 1 of the TMS3705E. This was done to provide a DC path to ground for the first stage amplifier that has been described in other documentation.
The image below shows the FFT (20msec transponder transmit) at the input to the TMS3705E before the AC coupling cap. The signal level at pin 2 (output of first stage amplifier) of the TM#3705E is about 10dB higher. The TMS3705 mode control register is programmed with the Division factor adapting automatically (DATA_BIT [4:1] = 1111). The transponder is positioned about 8 inches above the antenna loop in the optimal orientation to receive and transmit EM energy. With the transponder at this height (8 ") above the antenna the data is being read about 50% of the time, so basically at the limit of the read range.
We would like more read range so I have attempted to increase the gain of the differential to single-ended amplifier but the resulting improvement in read range is not happening. One question that I need your help with is what signal level should we be providing to the TMS3705 (or can we provide) to increase the read range? Is the current signal level too high, not high enough, too noisy? Are there other factors to consider to achieve more read range?
Best regards,
Jim