A 400µW 3rd Order LPF with -5 to 27dB Variable Gain for 3G Direct Conversion Receiver in 180nm CMOS Technology

Abstract

Design of an ultra low power channel select filter with variable gain for the direct conversion wireless 3G receiver is proposed. Portable wireless communication receiver requires a highly linear and low noise base band filter to achieve good sensitivity. Low power consumption is desirable for Portable systems. The proposed 3rd order continues time low pass filter consists of a pre passive filtering stage followed by an OPAMP stage. The pre passive filtering section with minimum number of resistors and capacitors provides high out band linearity and good spurious free dynamic range (SFDR) of the receiver. The single OPAMP stage provides four pole transfer function and reduces in band noise by the use of Cascode structure. Finally, inclusion of a variable gain stage, improves the system suitability for the practical applications. The simulated results of the proposed filter show 12 dBm of Input referred 3rd order intercept point (IIP3),33 dBm of out of band IIP3, with 2.5MHz 3dB frequency. The circuit shows -5 to 27dB variable gain by consuming 400µW power from 1.8V supply in 180nm CMOS.