A 90nm-CMOS 1.8mW 87dB-SNR 3rd order analog filter for GSM receivers

A 3rd order continuous time low pass filter for a GSM Receiver is presented. The filter uses the cascade of two active RC cells. The cut-off frequency deviation due to the technological spread, aging and temperature variation is adjusted by an on-chip tuning circuit. Fine definition (based on filter quality factor sensitivity functions) of the opamp frequency response and thermal/flicker noise optimization provides accurate filter transfer function. No miller cap tuning is needed, saving area and linearity. The device in 90 nm CMOS technology consumes 1.8 mW, features 87dB-SNR and 48 muVrms in-band integrated noise. The supply voltage is 1.2 V. The filter has been designed using an automatic Matlab design procedure which is validated by the agreement between the simulation results and the expected performance.