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RFID external hf power amplifier not working.

subhabrata mazumder
Prodigy 150 points
Other Parts Discussed in Thread: TRF7970A

We are trying to make a hf power amplifier for trf7970a RFID reader as per Texas instruments app note no.3348 but it is not reading tags supported by ISO15693.We are getting proper graph as mentioned in the app note.After a long investigation of the whole circuit we did not find any way out to overcome this problem....Please suggest me what to do...    

  • 0
    TI__Mastermind 44030 points

    Hello Subhabrata,

    Can you provide some more details?

    What is the tag size?  Even with an amplifier, you wont be able to obtain proper coupling to read a very small tag with a large reader antenna.

    Reader antenna size? 

    Did you offset the tuning of the antenna to reduce saturating the transmitter as mentioned in the note?

    Can you confirm that the RF field is turning on?  What voltage, Vpp, do you see across the coil?

    Do you receive some error from the TRF79xx when trying to read the tag or just no response?

    Did you set bit 6 in the Regulator & I/O register to enable external amp? 

  • 0 in reply to Eddie LaCost
    TI__Expert 3550 points

    Hello Subhabrata,

    A few other questions to help narrow down on the root cause:

    1. Can you provide oscilloscope screnshots of the signals compared to the app note?

    2. What code example are you using on host MCU to initialize the transceiver?

    3. Are you setting BIT 6 in the Regulator and I/O Control register to enable the external amplifier?

    4. Have you tried reading other tags (Type 2, Type 3 or Type 4B)?

    Thanks,

    Erick M.

  • 0 in reply to Erick Macias
    Prodigy 150 points
    Dear sir,
    Sorry for the late reply.The antenna is measured in VNA and it is providing proper S11 response.It is also working fine with other high power RFID systems.The voltage across the loop is measured around 114v. But no reply is coming from the trf7970 after placing the tag into the interrogation zone.We only need to read the inventory of the tag.We have written 0x01 to ISO Control,0x21 to Chip State Control,0x21 to IRQ mask,0xc7 to regulator and i/o control ,0x29 to Modulator and sys clk control.Is there any other register which we need to set.