Temperature-Compensated dB-linear Digitally Controlled Variable Gain Amplifier With DC Offset Cancellation

This paper presents a compact digitally controlled variable gain amplifier (DVGA) with capabilities of both temperature compensated linear-in-decibel (dB-linear) gain control and dc offset cancellation (DCOC) without making use of either the feedback or the feed-forward loop. The proposed DVGA design is a three-stage inductorless cascaded amplifier that is integrated with a temperature-compensated dB-linear gain control, a DCOC, an output common mode feedback, a 6-bit digital gain control (with a 64-step resolution), a power shutdown mode, and a linearizer for improving the 1-dB gain compression point. The design is fabricated using a commercial 0.18-μm SiGe BiCMOS technology. The DVGA has a measured gain range of 18.4 dB with an average step size of 0.3 dB, a 3-dB bandwidth from 2 MHz to 1.9 GHz with a ±0.75-dB gain flatness from 2.75 MHz to 1.2 GHz, an input 1-dB gain compression point better than -12.5 dBm, an input return loss better than 12 dB, an output return loss better than 16 dB, and a dc power consumption of 12.2 mW from a 1.8-V supply. The core DVGA, by excluding the I/O measurement pads, occupies a die area of 160 μm × 300 μm.