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OOK vs FSK vs ASK | Difference between OOK, FSK, ASK modulation

This page compares OOK vs FSK vs ASK and describes difference between OOK, FSK and ASK modulation techniques.

OOK Modulation | ON OFF Keying Modulation

OOK modulation

The figure-1 depicts OOK modulation technique. OOK stands for On Off Keying. OOK is modified version of ASK modulation.

While in ASK modulation logic-0 is represented by lower amplitude and logic-1 is represented by higher amplitude; in OOK modulation there is no carrier during the transmission of logic zero. The carrier is transmitted during the transmission of logic one.

In OOK modulation transmitter goes to IDLE state during transmission of logic "zero". This will help in conserving battery power.

OOK signal diagram

The figure-2 depicts OOK signal diagram. Here φ1 and φ2 represent signal vectors or complex data. The additive noise is represented by dotted circle around the main signal points. As shown one vector (φ1) represent some amplitude on X-axis while the other vector (φ2) represent zero value.

As carrier wave is present and absent at two different logic states, this modulation type is known as ON OFF Keying or OOK modulation.

ASK Modulation | Amplitude Shift Keying Modulation

ASK modulation

The figure-3 depicts ASK modulation and FSK modulation techniques. ASK stands for Amplitude Shift Keying. In ASK modulation, modulating input is digital and carrier is analog. The carrier wave is present with higher amplitude(i.e. A2 as shown) in ASK modulated output where binary input is 'one' is to be transmitted. The logic zero is transmitted with lower amplitude (i.e. A1) compare to logic-1.
Also Refer 10ASK and 100ASK modulation >> used in NFC technology.

ASK signal diagram

The figure-4 depicts ASK signal diagram. As shown one vector (φ1) represent higher amplitude compare to the other vector (φ2). The higher the difference between the two amplitudes, easier to detect and decode the data signal points at the receiver.

As amplitude value is shifting in transition from one binary logic to the other, this modulation type is known as amplitude shift keying.

FSK Modulation | Frequency Shift Keying Modulation

FSK modulation

FSK stands for Frequency Shift keying. In FSK modulation, modulating input is digital and carrier is analog. Modulated output will have frequency of f1 when binary input is 'one' and it will have frequency of f2 when binary input is 'zero'. Also refer 2FSK vs 4FSK modulation >>.

FSK signal diagram

The figure-5 depicts FSK signal diagram. As shown one signal vector (φ1) is represented by some phase and the signal vector is represented by different phase point. These phase points represent two different frequencies. As frequency value is shifting in transition from one binary logic to the other, this modulation type is known as frequency shift keying.

➨FSK modulation performs better compare to OOK/ASK in the presense of interference.
➨ASK modulation offers benefits of being more immune to interference compare to OOK modulation.
➨It is easier to implement ASK at lower cost compare to FSK modulation.
➨OOK modulation extends battery life as there is no carrier being transmitted during logic-0. Hence during this time transmitter can be in IDLE state.

The above mentioned comparison between OOK, ASK and FSK will help in selecting the right modulation for the need.

BPSK, QPSK, QAM, MSK, GMSK, PSK Modulation Types

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