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 that has more than a decade frequency coverage. The chip consists of two parallel transmitters that are both fully operational from 100 MHz up to 1.1 GHz. Using a single-ended current-mode output topology, the radio-frequency (RF) output signals are lossless combined by summing the output currents. The third-order harmonic of the oscillator signal is filtered by a wide-band polyphase filter. The complex filtering operation is mathematically described in this paper. The on-chip integrated oscillators have a measured 55-1200 MHz tuning range. Using the polyphase filter, a linear mixer topology, and a linear output driver, all distortion components are below -40 dBc. All intermodulation products of the two channels are smaller than -48 dBc. In this way, it is guaranteed that the parallel channels do not disturb the other channels in the frequency band even without any channel-specific filtering. Each channel delivers the designed -16-dBm RF output signal. The measured transmitter noise floor is situated at -139.8 dBc/Hz. The chip has been processed in a standard 0.5 /spl mu/m CMOS technology.