(A) wideband/high dynamic range CMOS variable gain amplifier (VGA) for low supply voltage wireless applications

Abstract

This thesis presents a new wideband and high dynamic range CMOS VGA at low supply voltage for wireless applications. To achieve conflicting performances such as high linearity and low noise figure (NF) with constraints of low power dissipation, it is necessary for VGA to have an accurate gain control function and a wideband gain cell (VGA cell) with high gain at low voltage. This CMOS VGA employing a new gain stage cell with an active load for wideband operation is presented workable at low supply voltage such as under 1.8V. It employs multistage architecture and combines three gain stages with both temperature and process compensated gain control circuit to satisfy the specifications of wireless communications. New VGA cell is proposed to achieve both high dynamic range and wideband at low supply voltage. A new current sharing bias scheme improves the dynamic range and linearity. With its smaller bias current, higher linearity due to better IP3 in low gain control range is acquired for high dynamic range. Wideband operation is also achieved using novel active load with gain boosting. There is an improvement of -3 dB band-width over 31 % owing to gain boosting technique. In a proposed exponential function generator with control voltage scaler (CVS), it is possible to compensate some deviations of its slope against temperature variations. Due to both process and temperature compensation of exponential function, total gain error is reduced by about 10 dB at 85℃. VGA IC is fabricated using 0.18㎛ CMOS technology. The active area of VGA is 440㎛×440㎛. It consumes under 3 mA at 1.8 V supply voltage. The gain in dB has a linear function of external control voltage $(V_c)$ with gain control range of 84 dB(from -42 dB to +42 dB). Its operating bandwidth shows up to 350 MHz. IIP3 varies from -22 dBm at +42 dB $(V_c = 1.8V)$ to +20 dBm at -42 dB $(V_c = 0.0V)$. Minimum NF is under +7 dB at +42 dB of gain. The suggested VGA in this thesis is thought to be suitable f...