Abstract
A novel low-loss image-reject mixer (IRM) using the source follower isolation method for digital radio mondiale/digital audio broadcasting applications is presented. It is based on double-quadrature mixers (DQMs) and passive polyphase filters (PPFs). The DQM is designed with four passive CMOS mixers. A source follower is inserted between the RF PPF and DQM to decrease the conversion loss of the IRM. Compared with the traditional isolation method, the source follower isolation method shows much higher on-resistance while looking into the RF port of the mixer; meanwhile, the chip area will be greatly decreased. This chip is fabricated in a 0.18-mu m CMOS technology. The total conversion loss is 10.5 dB, and the conversion loss per stage of PPFs is 2.1 dB on average. The image-reject ratio is larger than 40 dB in the bandwidth of 1.536 MHz without trimming and calibration. The P1dB gain compression point is 7.6 dBm. The chip core area is 1.1 x 1.3 mm(2).