Power line interface circuit diagram using carrier

Filter 18.432M

FSK, or Frequency-Shift Keying, is a digital modulation technique where the frequency of a carrier signal is changed to represent binary data. In this method, the baseband digital signal's discrete values are used to shift the carrier frequency between two distinct frequencies—typically referred to as the high (fH) and low (fL) frequencies. This allows for the transmission of digital information over an analog channel. Interestingly, FSK also has a slang meaning in some contexts, though it’s not commonly used in technical discussions.

The diagram below illustrates a power line communication interface using FSK technology. In this setup, the baseband signal switches between two frequencies: fH for one state and fL for the other. Unlike some other modulation schemes, FSK does not typically employ Hamming error correction coding. Instead, it relies on the inherent robustness of frequency changes to transmit data reliably.

The modulator can receive various types of data inputs:

• External Data Input: Can come from synchronous or asynchronous data interfaces, or from an m-sequence generator.
• All 1s Code: Transmits at the high frequency during test conditions.
• All 0s Code: Transmits at the low frequency when no data is present.
• 0/1 Alternating Pattern: A 0101 sequence used for general testing purposes.
• Special Code Sequence: A periodic sequence with a period of 7, designed for observation with a conventional oscilloscope.
• m-Sequence: Used to evaluate channel performance under different conditions.

This variety of input options makes FSK a flexible and widely used technique in applications such as power line communication, telemetry, and low-speed data transmission. Its simplicity and ease of implementation make it particularly useful in environments where noise and interference are common.