Integrated Variable Gain Amplifier and Active RC Ladder Filters

An integrated variable gain amplifier (VGA) and low pass filter (LPF) used in RFID reader are being presented here. The design consists of a preamp, a LPF followed by a VGA. The LPF is a fully differential ladder filter with option to switch into 2 modes. First mode is for listen before talk (LBT) mode with passband frequency of 331 kHz. Second mode is for Talk mode with passband frequency of 1.53 MHz. The VGA is able to provide programmable gain from 12 dB to 60 dB with 1 dB step and suppress the low frequency components below 4 kHz to cancel the DC offset. Both the control for LPF mode and VGA gain will be provided by baseband circuit. For the use of VGA control a received signal strength indicator (RSSI) circuits is also included. The designs have been implemented in 0.18-mum CMOS technology which consumes 56 mA for Talk mode and 71 mA for LBT mode from 1.8 V supply voltage.