alex2013
Junior Member level 2
Hi,
I am wondering what is the most commonly used rectifier circuit for NFC (near field RFID) card?
I am asking this because when I try using a three stage fullwave Dickson rectifier/charge pump, while I get the voltage multiplication (got 7V DC output from a 8V peak-to-to peak sine input in simulation) and the required DC current (I need around 6mA DC at the output), this requires large capacitors at the RF input (10 x 300pF, 6 for the positive side, 4 at the negative side of RF input. is this normal?), which means the input impedance of this rectifier is very low. This is undesirable because we need a large input impedance at rectifier for load modulation to work (NFC cards use load modulation to communicate with reader. That is, when modulating, to represent a '0' we simply short the RF nodes so that the impedance between those nodes falls to a very low value. But when the input impedance of rectifier is already very low, it becomes very difficult for the modulator to make an even lower impedance).
Another possibility is using bridge rectifier, but in this case we will not get voltage multiplication (CMIIW), so I think this is not usable (we need to account for when the card is slightly taken further from the reader which means low voltage at the output of antenna/coil).
Anyone care to comment? what is usually used in NFC cards?
I suspect a normal (far field) simple RFID tag, where the required DC current is much lower due to a simpler digital functionality, can use a dickson rectifier with smaller input capacitance (hence the proliferation of papers about RFID which use this circuit). But when larger DC current is necessary (like in NFC), this is not the case. Am I correct? There is very few papers or reference specifically about circuits used in an NFC card, most of them are about RFID tag.
I am wondering what is the most commonly used rectifier circuit for NFC (near field RFID) card?
I am asking this because when I try using a three stage fullwave Dickson rectifier/charge pump, while I get the voltage multiplication (got 7V DC output from a 8V peak-to-to peak sine input in simulation) and the required DC current (I need around 6mA DC at the output), this requires large capacitors at the RF input (10 x 300pF, 6 for the positive side, 4 at the negative side of RF input. is this normal?), which means the input impedance of this rectifier is very low. This is undesirable because we need a large input impedance at rectifier for load modulation to work (NFC cards use load modulation to communicate with reader. That is, when modulating, to represent a '0' we simply short the RF nodes so that the impedance between those nodes falls to a very low value. But when the input impedance of rectifier is already very low, it becomes very difficult for the modulator to make an even lower impedance).
Another possibility is using bridge rectifier, but in this case we will not get voltage multiplication (CMIIW), so I think this is not usable (we need to account for when the card is slightly taken further from the reader which means low voltage at the output of antenna/coil).
Anyone care to comment? what is usually used in NFC cards?
I suspect a normal (far field) simple RFID tag, where the required DC current is much lower due to a simpler digital functionality, can use a dickson rectifier with smaller input capacitance (hence the proliferation of papers about RFID which use this circuit). But when larger DC current is necessary (like in NFC), this is not the case. Am I correct? There is very few papers or reference specifically about circuits used in an NFC card, most of them are about RFID tag.
