The document discusses sense amplifiers, which are used in memory circuits to amplify weak signals from memory cells to recognizable logic levels. Modern sense amplifiers use 2-6 transistors, while early designs used up to 13 transistors. The key roles of sense amplifiers are amplification, delay reduction, power reduction, and signal restoration. Differential amplifiers are commonly used in SRAM as they offer a true differential output. Bit lines are precharged before reads and the sense amplifier is enabled once a sufficient signal is built up on the bit lines. Various types of sense amplifiers are discussed, including those based on inverters, charge redistribution, and single to differential conversion to overcome noise in larger memories.