A CMOS Variable Gain Amplifier with Wide Dynamic Range and Accurate dB-Linear Characteristic

Abstract

A novel CMOS variable gain amplifier (VGA) with high frequency, wide dynamic range and accurate dB-linear gain control for WCDMA direct-conversion receiver is proposed. To achieve conflicting performances such as high linearity and wide dynamic range with constraints of low power dissipation, it is necessary for VGA to have an accurate gain control characteristic and a wideband gain cell (VGA cell) with high gain at low voltage. Therefore, a new VGA cell is proposed to achieve both high dynamic range and wideband at low supply voltage. Wideband operation is also achieved using novel active load with gain boosting. In a proposed exponential voltage function generator using parasitic bipolar transistor, it is possible to compensate some deviation of its slope against temperature and process variations. The VGA has a controllable gain range of -20 dB ~+55 dB which can be controlled by adjusting the external control voltage and enhanced operating frequency range up to 150 MHz