Gm-C low-pass-filter designed for a Zero-IF base-band demodulator

A versatile 5
^th
order low-cost GM-C low-pass-filter for a Zero-IF base-band demodulation scheme is presented in this paper. The circuit is designed for a low-power 2.45GHz direct-conversion receiver based on frequency shift keying (FSK) modulation with a 2MHz corner frequency to provide rejection of the adjacent channels. Corner frequency of the proposed filter can be easily controlled from a DC bias current source. The circuit has been simulated under 2.5V using the 0.28μm standard CMOS process technology. The total output noise density is equal to 47nVrms at 2MHz. The corresponding total harmonic distortion is lower than 0.3% when a 2MHz-20mV peak-to-peak input sinusoidal voltage is applied. At the same simulation conditions and up to 8MHz, the circuit exhibits a frequency-rejected higher than 28dBc. The filter total silicon area is 100μm×100μm and the total current consumption is 180μA under 2.5V supply voltage.