TRF7970A, P2P, Test_AGC

Please see section 2 of the application note here ==> http://www.ti.com/general/docs/litabsmultiplefilelist.tsp?literatureNumber=sloa192 for the technique and register settings we recommend for intial RF collision avoidance. 

the code example is also a hyperlink on this page as well. 

Hello Josh,
Thank you for the quick reply and the link for this useful document. It provides hints to my other question on RX settings register (0x0A).

However it does not explain AGC_Test (Test Register (0x1A), Bit0) behaviour. We have no issue with RF collision avoidance. We just want to verify RF performance of our design and verify the AGC is working well.

Regards
Guenther

Guenther - 

are you now looking at the MOD pin output (enabled by B6 of register 0x1A) and even perhaps the ASK/OOK pin (enabled by B3 of register 0x09). What changes have you made to the reference schematic and layout designs that we publish?

Hello Guenther,

The AGC is most useful in noisy environments, thus you might not see a big difference in performance when you enable it depending on your system's environment.

AGC is applicable only in basic RFID receiver modes (passive initiator).

What concerns do you have about your RF system?

Best regards,

Erick M.

Hi Josh,

We adapted the schematic for Power Line Communication (PLC) and in a HW review phase. We solved issues in SW and able now to communicate with two TRF7970A over power line. Currently we evaluate the dynamic range of the path link and also verfy proper TRF settings. We operate OOK and use P2P communication as normal NFC. The only difference is the communication link. We even adapted your EVMs for this purpose.

On our review we switched on Test_AGC bit and monitored the RSSI bits at different RF levels. Our observation was that on increase RF level rssi_0_1_2 increased till 0x07 then rssi_x0_x1_x2 increased in steps till 0x07. The signal was fed by RX_IN2 and RF matrix set to RX_IN2 as main port.

On our observation the agc seems to work as the decoding range extended to 20dB.

Unfortunately the datasheet does not express how Test_AGC impacts rssi_0_1_2 and other bits. That's why I raised this question.

Regards

Guenther

Hello Eric,

Yes, we are in a noisy environment. We use it for PLC. So dynamic range of decode and interference immunity are chalenges to overcome. In using P2P the initiator and target acts like two way communication this means pasive initator and active target in answer mode.

As we use the RX_IN1 and RX_IN2 with different RX amplifications (LMH6611 does a good job), we currently evaluate that we have no gap between the two decode ranges (RX_IN1, RX_IN2). That's why we want to use Test_AGC to verify performance.

Regards
Guenther

Hello Josh, Eric,

We went on with further tests at different RF levels by adding attenuators between the RF communication ports. The AGC was enabled and TEST_AGC bit set. Here are the result of our measurement:

It seems to me that rssi_012 shows the RF level on main path and rssi_345 reports agc attenuation setting. But TRF7970A datasheet says different (6.14.3.4.1 Test Register (0x1A)).

Regards
Guenther