1. A variable gain amplifier circuit comprising: an operational amplifier for amplifying and outputting an input signal according to a cutoff frequency and a gain; a feedback resistor for changing a first resistance according to a first digital control code value which determines the cutoff frequency; and an input resistor for changing a second resistance according to a second digital control code value which is determined based on a difference of the first digital control code value and a gain code value, wherein the gain is determined by a ratio of the first resistance and the second resistance and linearly changes on a decibel (dB) basis according to the first digital control code value, and wherein the cutoff frequency is inversely proportional to the first resistance and linearly changes on a log scale.