An amplifier circuit is disclosed that allows for practical integrated circuit implementation of a dc-blocked, low-noise differential amplifier capable of amplifying ultra low-frequency signals and amplitudes ranging upwards of a few microvolts. DC-blocking capacitors having a capacitance value close to that of the effective input capacitance of the low-noise amplifier's inputs can be used by incorporating a positive feedback mechanism that tracks any variations in the amplifier gain or integrated circuit's technology process and lowers or cancels the input parasitic capacitances. Advantageously, the parasitic capacitance of transistors, typically field effect transistors, located on an integrated circuit chip are used in the feedback mechanism. This reduces the capacitive voltage division loss of the signal at the input of the amplifier while still allowing for the use of very small values of dc-blocking capacitance. No other active elements other than the amplifier itself are required to attain a low area, integrated circuit implementation of a dc-blocked, yet ultra low-frequency high pass filtered, low-noise amplifier.
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