An Improved Linearity, Single Stage Variable Gain Amplifier Using Current Squarer for Wider Gain Range
A novel single stage variable gain amplifier (VGA) based on transconductance $g_{m}$gm ratio amplifier is analyzed and designed with wider linear in dB gain range and improved linearity. The variable gain amplifier proposed here consists of an exponential control block, a current squarer and an amplifier block with both input and load degeneration. With the help of current squarer which gets square function of the output current from exponential control block, the VGA achieves the maximum linear gain range in single stage. Current squarer is proposed, which is designed with compensation technique to minimize the second order effect caused by carrier mobility reduction in short channel MOSFET. To avoid the poor linearity performance of the $g_{{m}$gm ratio amplifiers, the distortion is analyzed and the linearity is improved by applying input and load degenerating technique. At the same power consumption, the input 1 dB compression point can be improved by nearly 8.78 dB. Simulation results show that the VGA can provide a gain variation range of 64.09 dB (from 35.59$ 35.59 to 28.5 dB) with a 3 dB bandwidth from 47 to 640 MHz. The circuit consumes the maximum power 3.5 mW from a 1.8 V supply.
Circuits Syst. Signal Process.