Syllabic companding baseband switched capacitor filter for WLAN 802.11a/g receivers

The IEEE WLAN 802.11a/g standard requires short time interval (5.6 mus) for automatic gain control (AGC) convergence during reception of the preamble in each data packet. Due to this stringent settling time requirement, most of the AGC is implemented after the baseband filter, which leads to high power consumption in the baseband filter. In this paper, we present syllabic companding using switched capacitor (SC) ciruits as a solution to achieve gain control in the baseband filter without sacrificing any of the AGC settling time. A 5^th order syllabic companding, Chebyshev type, SC filter with a cut-off frequency of 10 MHz is implemented in IBM´s 1.2 V, 130 nm CMOS technology. The filter consumes a total power of 45 mW. It is estimated that companding by a factor of 4 achieves 12 dB improvement in dynamic range and a reduction in power consumption by a factor of 4.3 with respect to conventional filters.