A pseudo-Gaussian filter and sigma-delta modulator for IEEE 802.11a/b/g transmitter

This paper presents two components of an indirect modulation transmitter: a low-cost pseudo-Gaussian filter (PGF) and a modified third-order sigma-delta modulator (SDM) for WLAN 802.11a/b/g or Bluetooth. The PGF is a Gaussian filter quantized with 4 bits and is implemented using look up table method. The SDM is a modified feed forward third order modulator with local feedback to enhance signal-to-noise ratio (SNR). With a reference clock of 16 Mhz frequency, the components are designed to work at a transmission rate of up to 1 Msymbols/s. Simulation results show that the circuits work well and the noise is less than -90 dB at 3 Mhz offset frequency. The combination of the two circuits is implemented in 0.18-um CMOS technology, occupying an area of 147 um X 147 um.