because the Schottky diode prevents the transistor from saturating and storing charge; see Baker clamp. Gates built with Schottky transistors use more power than normal TTL and switch faster. With Low-power Schottky (LS), internal resistance values were increased to reduce power consumption and increase switching speed over the original version. The introduction of Advanced Low-power Schottky (ALS) further increased speed and reduced power consumption. A faster logic family called FAST (Fairchild Advanced Schottky TTL) (Schottky) (F) was also introduced that was faster than normal Schottky TTL. Complementary MOS (CMOS) logic CMOS logic gates use complementary arrangements of enhancement-mode N-channel and P-channel field effect transistor. Since the initial devices used oxide-isolated metal gates, they were called CMOS (complementary metal–oxide–semiconductor logic). In contrast to TTL, CMOS uses almost no power in the static state (that is, when inputs are not changing). A CMOS gate draws no current other than leakage when in a steady 1 or 0 state. When the gate switches states, current is drawn from the power supply to charge the capacitance at the output of the gate. This means that the current draw of CMOS devices increases with switching rate (controlled by clock speed, typically). The first CMOS family of logic integrated circuits was introduced by RCA as CD4000 COS/MOS, the 4000 series, in 1968. Initially CMOS logic was slower than LS-TTL. However, because the logic thresholds of CMOS were proportional to the power supply voltage, CMOS devices were well-adapted to battery-operated systems with simple power supplies. CMOS gates can also tolerate much wider voltage ranges than TTL gates because the logic thresholds are (approximately) proportional to power supply voltage, and not the fixed levels required by bipolar circuits. The required silicon area for implementing such digital CMOS functions has rapidly shrunk. VLSI technology incorporating millions of basic logic operations onto one chip, almost exclusively uses CMOS. The extremely small capacitance of the on-chip wiring caused an increase in performance by several orders of magnitude. On-chip clock rates as high as 4 GHz have become common, approximately 1000 times faster than the technology by 1970. Lowering the power supply voltage CMOS chips often work with a broader range of power supply voltages than other logic families. Early TTL ICs required a power supply voltage of 5V, but early CMOS could use 3 to 15V. Lowering the supply voltage reduces the charge stored on any capacitances and consequently reduces the