A PIN Diode SiGe HBT Variable Gain Amplifier for WCDMA Applications
We report a novel PIN diode SiGe HBT variable gain amplifier (VGA) suited for the standard of WCDMA. The PIN diode which is employed in the feedback loop of the VGA play as a variable resistor to realize the gain control function. By adjusting the bias of the diode, the gain of the VGA can be changed. An inductor is utilized in the feedback loop to reduce the noise figure of the circuit. After matching the circuit, we get a variable gain amplifier with 21dB dynamic range, about 19dB maximum gain, and 2.6dB minimum noise figure. This work demonstrates a new method controlling the gain by adding a PIN diode in the feedback loop except changing the bias of the transistor.