An ultra-low and adjustable high-pass corner frequency variable gain amplifier using T-type pseudo-resistor

Variable gain amplifier (VGA) is an important building block for biomedical communication system. It can amplify the variable amplitude of input signal by corresponding gain stage which provides stable signal for analog-to-digital converter (ADC). The amplitudes of common physiological signals, such as ECG, EMG and EEG, are in order of tens of uV to tens of mV and the frequencies span from tens of mHz to a few kHz. The VGA should have the features of low input referred noise, reconfigurable bandwidth, low THD, and variable gain to meet requirements of different biomedical applications[1].In order to ensure that the low cut-off frequency of VGA lower than the lowest frequency of all useful input signals, an appropriate ultra-low high-pass corner frequency must be designed.