Design of a CMOS active RC baseband channel filter for a direct conversion WCDMA receiver

The direct conversion receiver architecture achieves a high integration level because off-chip passive image and channel selection filters are not needed like in superheterodyne. The channel selection can be performed with integrated analog or digital filters. This paper reports the design of a baseband channel selection for a 3G WCDMA direct conversion receive, which consists of a channel selection filter with automatic tuning scheme and a programmable gain amplifier (PGA) merged into filter chain. The design provides solutions to some known problems of direct conversion receivers such as DC offset (DC servo feedback technique). Active RC integrator is used in the filter chain (5th-order Chebyshev with 0.01dB ripple and -3 dB frequency close to 2 MHz) and a fully differential telescopic two-stage operational amplifier is chosen.