一种基于T型伪电阻的可调超低高通角VGA

A VGA with Tunable Ultra Low High-Pass Corner Frequency Based on T-Shape Pseudo-Resistor

为了对超低频率的生物医学信号进行有效地调节和放大,提出了一种应用于VGA直流偏置电路的阻值可调的T型伪电阻网络,其超大的等效电阻与反馈电容形成的RC高通滤波环路可构成VGA的超低高通角。电路采用SMIC 0.18μm CMOS工艺进行设计和验证,后仿真结果表明,其高通角调节范围为0.16~410.8mHz,增益以3dB步长从10~49dB变化,等效输入噪声达2.7μV（rms）,总谐波失真（THD）仅为0.30%,具有高通角频率超低且可调、输入噪声低和THD低等特点,适用于高精度的人体心电信号采集等生物医学系统。

In order to effectively regulate and amplify ultra low frequency biomedical signal, a tunable T-shape pseudo-resistor was proposed as a DC bias circuit in variable gain amplifier （VGA）. Its ultra large equivalent resistance and feedback capacitance consisted of a RC feedback loop with a function of high-pass filter for VGA. The VGA was designed and optimized in SMIC 0.18μm CMOS technology. Post-simulation results showed that an ultra-low high-pass corner frequency was achieved with a tunable range from 0.16 mHz to 410.8 mHz. Furthermore, the gain of VGA could be varied from 10 dB to 49 dB with 3 dB increment. The equivalent input noise of VGA was 2.7 μV（rms） and total harmonic distortion（THD） was only 0. 30%. This VGA had the advantage of tunable ultra low high-pass corner frequency, low input noise and low THD, which was very suitable for high precision ECG signal acquisition and other biomedical system.