10% ASK modulation vs 100% ASK modulation-Difference between 10% ASK modulation and 100% ASK modulation
This page compares 10% ASK modulation vs 100% ASK modulation and mentions difference between 10% ASK modulation and 100% ASK modulation waveforms.
This NFC tutorial also covers following sub topics:
How NFC Works NFC Modulation and coding NFC Tag vs NFC Reader NFC Tag Types NFC-A,NFC-B,NFC-F difference between bluetooth,wifi,RFID and NFC NFC Tools and Equipments
About ASK Modulation:
As we know ASK is the short form of Amplitude Shift Keying. In this technique, binary 1 and binary 0 is mapped as carrier and no carrier respectively. It is represented by following equation.
Output = A* cos(2*π*fc*t) for binary logic-1
Output = 0 for binary logic-0
As the amplitude of the RF carrier varies based on binary input, it is known as amplitude shift keying modulation.
Refer ASK modulation vs FSK modulation vs PSK modulation for more information.
10% ASK Modulation
NFC uses type-A and type-B signaling methods as defined in ISO/IEC 14443 part-2. Communication between NFC devices is half duplex with 106 kbps data rate in both the directions.
10% ASK modulation type is used in type-B PCD (Proximity Coupling Device (Reader/Writer)). As mentioned Type B signaling type uses 10% amplitude modulation of RF field for communication from reader to card with NRZ encoding. Communication from card to reader uses BPSK modulation using 847.5 KHz with NRZ-L encoding. RF field is continuously ON here.
Figure depicts waveform for the ASK modulation.
Modulation index is defined as ratio of (A-B) and (A+B) as expressed below.
Modulation Index = (A-B)/(A+B) ,
A = Unmodulated signal amplitude
B = Modulated signal amplitude
Modulation Depth = B/A
10% ASK modulation means ASK modulation in which modulation index will range between 8% and 14%. The figure-1 depicts 10% ASK modulation waveform.
100% ASK Modulation
It is used in type-A PCD. 100% amplitude modulation of RF carrier is used for communication from reader to card with modified miller encoding. Communication form card to reader uses OOK modulation of 847.5 KHz subcarrier with manchester encoding. In 100% ASK modulation, unmodulated signal amplitude and modulated signal amplitude is almost equal. The figure-2 depicts 100% ASK modulation waveform.
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