Differential CircuitsSingle-Ended vs. Differential EndedAdvantages of Differential CircuitsCosts of Differential Circuits1Differential CircuitsDr. David W. GrahamWest Virginia UniversityLane Department of Computer Science and Electrical Engineering© 2010 David W. Graham2Single-Ended vs. Differential Ended• Single-ended signals– Referenced to a fixed potential (usually ground)• Differential signals– Measured between two nodes that have equal and opposite signal excursions about a fixed potential– The two nodes [must] have equal impedances to that fixed potential– The fixed potential is called the “common-mode” (CM) level– Generally, a signal is defined as the difference between V1 and V2• V1 –V2 = ΔV = Vid0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 100.20.40.60.811.21.41.61.8Tim e (s )Voltage (V)V1V2Vcm3Advantages of Differential Circuits• Common-Mode Rejection– Rejects “environmental” noise (noise produced by the environment or other circuits)– This noise will be “common” to both signals and will eventually be subtracted out• Power-Supply Rejection– Reduces the noise contributed by noisy power supplies• Increases/doubles the maximum achievable voltage swings• Increased Linearity– Removes even-order harmonics in fully differential systems• Typically simpler to bias4Costs of Differential Circuits• Increased area– In reality, the benefits far outweigh this minor detail– Single-ended circuits may consume more area to achieve the same performance• Twice the power consumption– (Similar concepts as