Low-Voltage Improved Accuracy CMOS VGA Circuit

The paper presents a 100dB-linear VGA circuit, designed for a low-voltage operation, having a multitude of applications, such as synthesizers, amplitude modulation and audio level compression. The original design method proposes the approximation of the exponential function by implementing a new fourth-order approximation function that allows to obtain high accuracy of the circuit and a wide decibel linear range (100dB), considering a deviation from the exponential function equal with ± 1dB. The proposed variable gain amplifier presents the advantage of current-mode operation that increases the circuit frequency response. An additional increasing of the exponential function accuracy represents a consequence of the independence of the output signal on technological-caused errors and also on temperature. The circuit is designed for an implementation in 0.18μm CMOS technology on a chip area of approximately 12μm2, being characterized by a low-voltage low-power operation (a supply voltage of 0.9V and a maximal current consumption smaller than 1.9μA).