If "M" is also biased with zero "V" and provided transistors "M" and "M" have good matching of their properties, such as channel length, width, threshold voltage, etc., the relationship "I" = "f"("V", "V" = 0) applies, thus setting "I" = "I"; that is, the output current is the same as the reference current when "V" = 0 for the output transistor, and both transistors are matched.