A sense amplifier includes: a pull-down device which contains a reference cell which is structurally identical to the PLD cells being sensed; and a pull-up device connected to form a current mirror which causes a saturation current of the pull-up device to be zero or greater than the current through the sensed cell. The pull-down device has a saturation current which tracks the current through the sensed cell. When current flows through the sensed cell, saturation current through the pull-up device exceeds the saturation current through the pull-down device, and an output node is pulled up. When no current flows through the sensed cell, no current flow through the pull-up device, and the pull-down device pulls the output node down. As a result, the sense amplifier exhibits a variable trip point which tracks variations cause by changes in device fabrication process, temperature, and power supply voltage. The reference cell in the sense amplifier conducts a current only during sensing, and therefore consumes no standby power.