A 2.4 GHz Input Cascaded CMOS Variable Gain Amplifier with 50 dB Gain Control for RF Applications

Variable Gain amplifiers (VGAs) are essential front-end amplifiers in Radio Frequency (RF) communication systems, enabling efficient signal processing through dynamic gain control. This paper presents two distinct RF VGA designs integrated using Cadence GPDK 180 nm technology, each with a specific gain-control mechanism. The first design is based on resistive tuning with differential NMOS input pairs, achieving gain control by varying load resistances. The second design employs gate-controlled transconductances (gm) tuning through active load MOSFETS. Each design incorporates LC matching networks to ensure impedance matching and allow maximum power transfer at a frequency of 2.4 GHz. The simulated results demonstrated that resistive-tuning VGA achieves a wider bandwidth of 2 GHz while that of gm-tuning 583.7 MHz and increase of gain up to 50 dB upon cascading five VGAs. Parametric and temperature variation analysis reveals that the resistive-tuning VGA provides greater stability, whereas gm-tuning VGA offers precise gain control but is more sensitive to process variation maintaining stable operation up to 30°C. The input-referred noise recorded 3.5 nV/-VHz for maximum gain control and output power at 1 dB (OPIdB) 5.4 dBm.