In textbooks, channel length modulation in active mode usually is described using the Shichman–Hodges model, accurate only for old technology:[1] where I D {\displaystyle I_{D}} = drain current, K n ′ {\displaystyle K'_{n}} = technology parameter sometimes called the transconductance coefficient, W ,L = MOSFET width and length, V G S {\displaystyle V_{GS}} = gate-to-source voltage, V t h {\displaystyle V_{th}} =threshold voltage, V D S {\displaystyle V_{DS}} = drain-to-source voltage, V D S , s a t = V G S − V t h {\displaystyle V_{DS,sat}=V_{GS}-V_{th}} , and λ = channel-length modulation parameter. In the classic Shichman–Hodges model, V t h {\displaystyle V_{th}} is a device constant, which reflects the reality of transistors with long channels.