10% ASK vs 100% ASK Modulation: Differences Explained

This page compares 10% ASK modulation and 100% ASK modulation, highlighting the differences between their waveforms. This information is relevant to NFC (Near Field Communication) technology, and this tutorial also covers the following subtopics:

• How NFC Works
• NFC Modulation and Coding
• NFC Tag vs. NFC Reader
• NFC Tag Types
• NFC-A, NFC-B, NFC-F differences
• Bluetooth, Wi-Fi, RFID, and NFC comparisons
• NFC Tools and Equipments

About ASK Modulation

ASK stands for Amplitude Shift Keying. In this modulation technique, binary 1 is represented by the presence of a carrier signal, while binary 0 is represented by the absence of a carrier signal.

The equation representing ASK is:

• Output = A * cos(2* π * fc * t) for binary logic-1
• Output = 0 for binary logic-0

Where:

• A = Amplitude of the carrier signal
• fc = Carrier frequency
• t = Time

Since the amplitude of the RF carrier changes based on the binary input, it’s called Amplitude Shift Keying modulation.

10% ASK Modulation

NFC utilizes type-A and type-B signaling methods, as defined in ISO/IEC 14443 part-2. Communication between NFC devices is half-duplex, with a 106 kbps data rate in both directions.

10% ASK modulation is used in type-B PCD (Proximity Coupling Device - Reader/Writer). Type B signaling uses 10% amplitude modulation of the RF field for communication from the reader to the card, using NRZ (Non-Return-to-Zero) encoding.

Communication from the card to the reader uses BPSK (Binary Phase Shift Keying) modulation at 847.5 KHz with NRZ-L encoding. The RF field remains continuously ON.

Modulation Index is defined as the ratio of (A-B) to (A+B):

Modulation Index = (A-B) / (A+B)

Where:

• A = Unmodulated signal amplitude
• B = Modulated signal amplitude

Modulation Depth is defined as:

Modulation Depth = B/A

10% ASK modulation implies that the modulation index ranges between 8% and 14%.

100% ASK Modulation

100% ASK Modulation is used in type-A PCD. It involves a 100% amplitude modulation of the RF carrier for communication from the reader to the card, using modified Miller encoding.

Communication from the card to the reader uses OOK (On-Off Keying) modulation of an 847.5 KHz subcarrier with Manchester encoding.

In 100% ASK modulation, the unmodulated signal amplitude and the modulated signal amplitude are almost equal.