A novel accurate dB-linear control circuit topology for variable gain amplifiers in BiCMOS technology

We present in this paper a novel accurate decibel linear control circuit topology for variable gain amplifiers. According to our knowledge, the proposed linear-in-dB control circuit features the simplest control mechanism and topology for current summing or current steering VGAs to date. Based on the proposed circuit topology, a wideband variable gain amplifier with accurate linear-in-dB gain variation is implemented in Tower Jazz 0.18μm SiGe BiCMOS technology. The simulation shows the designed wideband VGA operates up to 5.2GHz with a linear-in-decibel gain ranging from -50dB to +20dB. The VGA possesses nearly constant bandwidth over the gain variation range and dissipates about 6mA current from a single 1.8V supply. The simulated noise figure at maximum gain is less than 6.5dB when matched to 50Ω and the chip layout area is less than 0.3mm excluding pads.