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When the PN7160 is set to LPCD mode, it cannot be activated from LPCD mode using a 2×2 cm antenna

Using the “NFC Antenna Tool,” we designed a 2 cm × 2 cm on-board antenna for the PN7160 with a Q-factor of 20 and a target impedance of 11 Ω. Since this is a small antenna, we enabled the PN7160's DPC in accordance with the “PN7160 Frequently Asked Questions [AN13892].”

Under these conditions, if we do not enable the PN7160’s LPCD mode, the two PN7160 devices can communicate normally via P2P. However, if we enable the PN7160’s LPCD mode, the PN7160 will be unable to wake up from LPCD mode. Using the same driver, however, we can activate it from LPCD mode with a 2cm × 4cm antenna.

The LPCD TRACE messages from 2 cm × 2 cm antenna are:
D (6358097) PN7160_I2C: NCI << 0x6f 0x13 0x04 0x80 0x83 0x80 0x03
D (6358597) PN7160_I2C: NCI << 0x6f 0x13 0x04 0x80 0x83 0x80 0x03
D (6359107) PN7160_I2C: NCI << 0x6f 0x13 0x04 0x80 0x83 0x80 0x03
D (6359617) PN7160_I2C: NCI << 0x6f 0x13 0x04 0x80 0x83 0x80 0x03

Please refer to the attachment for the antenna design parameters.
And the CORE_SET_CONFIG_CMD is set to :
uint8_t NxpNci_CORE_CONF_EXTN[]={0x20, 0x02, 0x6B, 0x05, /* CORE_SET_CONFIG_CMD */
0xA0, 0x40, 0x01, 0x81,    /* TAG_DETECTOR_CFG */
0xA0, 0x41, 0x01, 0x10,     /* TAG_DETECTOR_THRESHOLD_CFG */
0xA0, 0x42, 0x01, 0x0F,   /* TAG_DETECTOR_PERIOD_CFG */
0xA0, 0x43, 0x01, 0x00,   /* TAG_DETECTOR_FALLBACK_CNT_CFG */
0xA0, 0x0B, 0x57, 0xE5, 0x05, 0x90, 0x6E, 0x0F, 0x4E, /* DPC_CONFIG*/
0x00, 0x40, 0x95, 0xB7, 0xAA, 0x40, 0x9F, 0xA7, 0x99,
0x53, 0x9F, 0x97, 0x99, 0x5D, 0x9F, 0x97, 0x99, 0x5F,
0x9F, 0x97, 0x00, 0x68, 0x9F, 0x07, 0x00, 0x6A, 0x1F,
0x07, 0x00, 0x74, 0x1F, 0x07, 0x00, 0x78, 0x1F, 0x07,
0x00, 0x7F, 0x1F, 0x07, 0x00, 0x81, 0x1F, 0x07, 0x00,
0x8B, 0x1F, 0x04, 0x00, 0x8C, 0x1F, 0x04, 0x00, 0x96,
0x1F, 0x04, 0x00, 0x98, 0x1F, 0x04, 0x00, 0xA1, 0x1F,
0x02, 0x00, 0xA9, 0x1F, 0x00, 0x00, 0xAF, 0x1F, 0x00,
0x00, 0xB8, 0x1F, 0x00, 0x00, 0xC2, 0x1F, 0x00, 0x00
};
Is this issue caused by antenna matching or by the register settings?

Re: When the PN7160 is set to LPCD mode, it cannot be activated from LPCD mode using a 2×2 cm antenn

Hello, thank you for your interest in our products.

There are some limitations with your setup that I would like to address.

Even though the 2x2cm antenna can be implemented is recommended to attempt using a slightly bigger antenna size.

I would also like to clarify that P2P isn't recommended by NFC Forum, we highly recommend using HCE and Read/Write Mode instead.

It is very possible that the antenna size of the initiator could be too small to cause a detuning of the target.

Have you attempted waking up the Reader from LPCD with a regular PICC like a card? What is the result of this?

Please share the Smith cart and schematics of your prototype for further review.

Re: When the PN7160 is set to LPCD mode, it cannot be activated from LPCD mode using a 2×2 cm antenn

Have you been able to measure the impedance of your antenna?
It seems to be relatively low.

Re: When the PN7160 is set to LPCD mode, it cannot be activated from LPCD mode using a 2×2 cm antenn

Thank you very much for your reply, but I don’t have a VNA at the moment. If I still can’t resolve the issue, I’ll go ahead and buy one. Do you have any other suggestions?

Re: When the PN7160 is set to LPCD mode, it cannot be activated from LPCD mode using a 2×2 cm antenn

Thank you very much for your response.

At present, our use of P2P is a compromise made for compatibility. We have re-optimized the antenna shape and PCB layout, but the issue persists. The first image in the attachment is the antenna schematic, with parameters generated using the ‘NFC Antenna Tool’; the second is the schematic for the PN7160 and its peripheral circuitry; the third and fourth images show the top and bottom views of the PCB layout; and the fifth image shows the parameters we entered into the NFC Antenna Tool. For both asymmetric and symmetric tuning scenarios, we set Q, target impedance, fEMC cutoff, and L0 to 20, 13 Ω, 22 MHz, and 20, 11 Ω, 14.6 MHz, respectively, in accordance with page 23 of AN13219 (PN7160 Antenna Design and Matching Guide). However, in both cases, the notification message from LPCD TRACE remains:
D (564760) PN7160_I2C: NCI << 0x6f 0x13 0x04 0x80 0x83 0x80 0x03.

Whether we use our fingers or a metal object to get close to the antenna, the measurement remains unchanged.

Re: When the PN7160 is set to LPCD mode, it cannot be activated from LPCD mode using a 2×2 cm antenn

We also referred to the “PN7160 Antenna Design and Matching Guide” and used the program to read the AGC value:

void Get_AGC (SemaphoreHandle_t Semaphore_PN7160_IRQ)

{

    uint8_t get[] = {0x2F, 0x3D, 0x04, 0x02, 0xC8, 0x60, 0x03};

    uint8_t Answer[255];

    uint16_t AnswerSize;

    while (1)

    {

        printf("\n");

        NxpNci_HostTransceive(Semaphore_PN7160_IRQ, get, sizeof(get), Answer, sizeof(Answer), &AnswerSize);

        if ((Answer[0] != 0x4F) || (Answer[1] != 0x3D) || (Answer[3] != 0x00))

        {

            printf("Error, cannot get parameter value\n");

        }

        else

        {

            printf("\n");

            printf("Measured AGC Value (LSB)= %.2Xh" , Answer[4]);

            printf("\n");

            printf("Measured AGC Value (MSB)= %.2Xh", Answer[5]);

            printf("\n");              

        }

    }

}

However, the result we obtained was strange; it is not listed in the TEST_ANTENNA_RSP return value list in document UM11495. The value we read is 0x06:
(7600) PN7160_I2C: NCI >> 0x2f 0x3d 0x04 0x02 0xc8 0x60 0x03
D (7600) PN7160_I2C: NCI << 0x4f 0x3d 0x01 0x06
However, UM11495 only mentions four possible results：

0x00: STATUS_OK
0x01: Test execution rejected (PN7160 in wrong state)
0x04: STATUS_TEST_EXEC_FAILED
0x09: STATUS_INVALID_PARAM
Others: RFU