A CMOS dual-channel, 100-MHz to 1.1-GHz transmitter for cable applications

A dual-channel wide-band transmitter for cable applications is presented th at has more than a decade frequency coverage. The chip consists of two para llel transmitters that are both fully operational from 100 MHz up to 1.1 GH z. Using a single ended current-mode output topology, the radio-frequency ( RE) output signals are lossless combined by summing the output currents. Th e third-order harmonic of the oscillator signal is filtered by a nide-band polyphase filter. The complex filtering operation is mathematically describ ed in this paper. The on-chip integrated oscillators have a measured 55-120 0-MHz tuning range. Using the polyphase filter, a linear mixer topology, an d a linear output driver, all distortion components are below -40 dBc. All intermodulation products of the two channels are smaller than -48 dBc. In t his way, it is guaranteed that the parallel channels do not disturb the oth er channels in the frequency band even without any channel-specific filteri ng. Each channel delivers the designed -16-dBm RF output signal. The measur ed transmitter noise floor is situated at -139.8 dBc/Hz. The chip has been processed in a standard 0.5 mu m CMOS technology.