LOW-POWER LOW-VOLTAGE MULTI-LEVEL VARIABLE-RESISTOR LINE DRIVE

摘要

A low-power multi-level pulse amplitude modulation (PAM) line driver using variable resistors is disclosed for transmitting digital data over controlled-impedance transmission lines. The driver comprises two push-pull variable resistor branches, and a middle variable resistor branch. The purpose of the two push-pull branches is to generate the target voltage level onto the line, and the middle branch ensures that at all times the effective parallel impedance of the resistors matches to the line impedance. The values of the variable resistors are selected by a decision combinational logic whose input is the raw data bits. The driver requires a supply voltage that is equal or higher than twice the maximum output signal level. This supply voltage can be the supply voltage supplied to the chip itself or a regulated supply voltage adjusted to result in a certain voltage swing. This invention discloses the design of a multi-level PAM driver for high-speed wireline communication, with up to four times improvement in power efficiency over conventional drivers. Two key requirement for high-speed line drivers are first generating the target voltage level onto the controlled-impedance line, and second being impedance matched to the line itself to eliminate signal reflections from the transmitter back to the line. The driver in accordance with the present invention satisfies both of these requirements at very high power efficiency.