Design of a constant-bandwidth variable-gain amplifier for LTE receivers

In this study, a constant-bandwidth variable-gain amplifier (VGA) is presented for long-term evolution (LTE) receivers. The presented VGA’s description is given with a newly proposed exponential-current generator, and also the common-mode feedback and the DC-offset cancellation (DCOC) circuits. The proposed exponential current generator is based on the Taylor series approximation in such a way that it can be expanded to meet the required gain control range. The simulations are performed using the TSMC 180 nm process technology with Cadence Analog Virtuoso. The VGA has a 45 dB gain control range, 180 MHz bandwidth, 15.7 dB m the third-order input-intercept point for minimum gain and below 20 dB noise figure for maximum gain which makes it convenient for LTE receivers. The simulations also show that the bandwidth of the VGA is fairly constant over the control range. Monte Carlo simulations reveal that by using a DCOC circuit, the VGA provides 30 dB output offset rejection. The overall power consumption of the circuit is 9.1 mW under a 1.8 V power supply.