This paper presents a fully integrated CMOS low-IF receiver working at L-band for DAB application. An imagerejection low noise amplifier (LNA) supplies over 30dB image rejection in the whole band. A calibration circuit improves matching of quadrature LO signals. Together with the quadrature weaver architecture, the receiver rejects the image signal more than 65dB. The receiver's noise figure is 4dB and OIP3 is 22dBm. The receiver is implemented in 0.25um CMOS process. The core die area is 9mm 2 .
I IntroductionDAB (Digital Audio Broadcasting) is the third generation broadcasting system that has more superior performance than AM or FM. It takes use of OFDM modulation and has a bandwidth of 1.5MHz. The satellite DAB works at L-band. Some papers [1]-[2] has designed discrete receiver for satellite communication. But an integrated receiver will greatly reduce the size and improve the performance. However, because the on-chip inductor has poor performance and large area, the high frequency, high image rejection filter in superheterodyne receivers cannot be integrated in IC process. The In-phase and quadrature (I/Q) structure is used so that the wanted signal and its image signal can be separated in digital domain. But mismatch between I/Q branches restricts the image rejection to only about 35dB [3]. Another way is to use weaver receiver, which is image rejection architecture. But it is also sensitive to matching of mixers.A monolithic CMOS receiver with high image rejection is designed to improve image rejection. The receiver takes use of quadrature weaver architecture [4], which supplies good image rejection performance. Moreover, the LNA contains a notch filter. It further rejects image signals. An improved LO driver reduces the mismatching between LO quadrature signals generated from a poly phase filter (PPF). All of these effects bring the image rejection to -65-dB.
II Circuit ImplementationThe receiver (showed in Fig.1) adopts low-IF quadrature weaver architecture. It avoids wandering DC offset and 1/f noise at low frequency. The six mixers in dashed frame compose double conversion structure. It is less sensitive to unbalance in the phase and amplitude of the RF and LO input signals of the mixers [5]. This means a better image rejection than traditional weaver architecture. o ff ch ip B P F active L P F active L P F A /D A /D V G A V G A L N A R F m ixer IF m ixer P G A V G A V G A I Q I Q calib ration circu it P olyp h ase filter O n e C h ip 8 d ivid er L O sign al gen erato r L O D river h igh freq uen cy a m p lifier IF m ixer IF m ixer IF m ixer P G A R F m ixer Fig.1 The block diagram of the receiver 1232