Sense amplifiers and sensing methods

Abstract

A sense amplifier for sensing the impedance between two terminals includes an amplification stage whose input is connected to one of the terminals. The input is connected to a power supply voltage VCC through two transistors in parallel. One transistor provides a high speed by providing a large current when the voltage on the input is low. Moreover, to increase speed and save power, that transistor turns off when the amplification stage input voltage is slightly above the amplification stage trip voltage. The other transistor provides a small current to pull the amplification stage input up almost to VCC to reduce the amplification stage power consumption. The small current does not interfere significantly with the pull-down speed. One of the amplification stage power terminals is connected to ground through current limiting transistors to reduce the amplification stage power consumption when the amplification stage input voltage is at its low value which is slightly below the trip voltage. A reference voltage generator controls one of the two transistors connecting the amplification stage input to VCC so as to prevent the low value of the amplification stage input voltage from converging to the trip voltage over a wide range of the VCC and processing variations.