Complex sentence: Some sensitive mixed-signal circuits, such as precision analog-to-digital converters, use sine waves rather than square waves as their clock signals, because square waves contain high-frequency harmonics that can interfere with the analog circuitry and cause noise.
Split into simpler sentences: Some sensitive mixed-signal circuits, such as precision analog-to-digital converters, use sine waves rather than square waves as their clock signals. Since square waves contain high-frequency harmonics that can interfere with the analog circuitry and cause noise.