A 170MHz quadrature down-converter in 0.8 µm BiCMOS for very low power pagers

Direct conversion architecture is highly desirable in applications such as watch pager receivers or receivers in wireless hearing aids, where space is absolutely at a premium and external components must be minimized. Current consumption is also severely constrained, making it necessary to realize each RF block with less than 100µA. This paper focuses on the quadrature generation required in image-reject mixers. It is pointed out that insufficient gmdue to insufficient current makes many existing solutions impractical. It is also sown that RC-CR circuits have excellent phase but poor amplitude characteristics. The latter can be remedied by saturating amplifiers. A 280µA quadrature down-converter is reported, which includes a 90° phase-shifter and two RF mixers at 170MHz. Measured image rejection is better than 40dB.