Trying to understand NFC ASK Modulation

This will be harder than you think !

A long time ago (2006) I did work designing antennae for MIFARE (same thing, more or less) and it's quite tricky.

NXP still are fairly active in this field and you can learn a lot from reading their app notes and data sheets, Here's a start:

https://www.nxp.com/products/rfid-nfc/nfc-hf/nfc-readers/nfc-cortex-m0-all-in-one-microcontroller-with-optional-contact-interface-for-access-control:PN7462

The antenna was two turns on a pcb (inner layers)  with earth shielding layers on both sides of the board and multiple vias to stich them togethher. There as a multi component passive matching network with an adjustable tuning cap. The pcb needed non standard layer stackup to work and we were discussing fine tuning the design of coil, copper thickness and pcb layer thicknesses. All backed up by impedance measurements with a home made network analyser (computer + sig gen + scope + active analogue interface pcb.

Sorry, can't post pics because customer might object (although they might not still exist  - actually they do, just checked and the two guys I worked with then are still there !).

MK

This will be harder than you think !

A long time ago (2006) I did work designing antennae for MIFARE (same thing, more or less) and it's quite tricky.

NXP still are fairly active in this field and you can learn a lot from reading their app notes and data sheets, Here's a start:

https://www.nxp.com/products/rfid-nfc/nfc-hf/nfc-readers/nfc-cortex-m0-all-in-one-microcontroller-with-optional-contact-interface-for-access-control:PN7462

The antenna was two turns on a pcb (inner layers)  with earth shielding layers on both sides of the board and multiple vias to stich them togethher. There as a multi component passive matching network with an adjustable tuning cap. The pcb needed non standard layer stackup to work and we were discussing fine tuning the design of coil, copper thickness and pcb layer thicknesses. All backed up by impedance measurements with a home made network analyser (computer + sig gen + scope + active analogue interface pcb.

Sorry, can't post pics because customer might object (although they might not still exist  - actually they do, just checked and the two guys I worked with then are still there !).

MK