A cable-modem RF tuner

In monolithic integration of cable-modem RF tuners a double-conversion receiver architecture is used. In this paper we present a prototype design of an upconverter and a downconverter unit. The upconverter upconverts a channel from 47-862 MHz input band to around 1575 MHz intermediate frequency. The image-reject downconverter shifts the channel to 36.125 MHz (EU) or to 43.75 MHz (US). The upconverter includes a variable-gain low-noise amplifier, a double balanced mixer, a three-stage VCO bank for LO generation and a divide-by-two circuit for driving an external PLL. The downconverter includes a LNA, image-reject mixers in Hartley configuration, a 3-stage polyphase filter, an IF-amplifier and a SAW driver. For LO generation the circuit includes a 6-GHz on -chip VCO, a divide-by-four circuit quadrature LO and a divide-by-16 for feeding an external PLL. Signal reversal switching in the LO buffer can be used for the selection of LSB/USB injection. All building blocks are presented in this paper and experimental results are given from the upconverter, downconverter, and RF tuner demonstrator including SAW filters with center frequencies at 1575 MHz and 44 MHz. the circuits are fabricated in a 0.9-/spl mu/m SiGe bipolar process.