The earliest implementations consisted of a reference ladder of well matched resistors connected to a reference voltage. Each tap at the resistor ladder is used for one comparator, possibly preceded by an amplification stage, and thus generates a logical 0 or 1 depending on whether the measured voltage is above or below the reference voltage of the resistor tap. The reason to add an amplifier is twofold: it amplifies the voltage difference and therefore suppresses the comparator offset, and the kick-back noise of the comparator towards the reference ladder is also strongly suppressed. Typically designs from 4-bit up to 6-bit and sometimes 7-bit are produced.