Patent ID: 6903593

Claim:
A gain amplifier with DC offset cancellation circuit, the gain amplifier having an input end coupled to an input signal source, comprising: a buffer, having an input end coupled to an output end of the gain amplifier, and an active low-pass analogue filter, coupled to the output end of the buffer, for filtering input analog signals at high frequencies, and feeding the filtered buffer output signals to the input end of the gain amplifier to be deducted from the input analog signals in order to obtain a negative feedback, so as to cancel DC bias, wherein the active low-pass analogue filter includes a variable resistor, an amplifier, a capacitor pair and a comparator, the amplifier being coupled to an output of the variable resistor, the negative feedback being provided from the output of the variable resistor to the input signal source, the capacitor pair being coupled to the amplifier, one input of the comparator being coupled to an output of the amplifier, and a second input of the comparator being coupled to a reference voltage source such that a comparison signal is output by the comparator to the variable resistor after comparing the negative feedback with a reference voltage.