A single CHIP transmitter for a spread spectrum direct sequence in-house communication system at 2.4GHz

The design of a single chip transmitter for a spread spectrum inhouse communication system working at 2.4GHz is presented. The circuit consists of a frequency doubler (1.2 to 2.4GHz), a double balanced modulator with an LO buffer amplifier, and a seven stage power amplifier for 100mW of output power. Except for the power amplifier output matching network, and a bandpass filter, no additional external components are required. Chip fabrication was performed with a commercial lmm-GaAs-MESFET enhancement/depletion foundry process. Through consequent use of an insensitive circuit design strategy, a high production yield is achieved. From 26 devices investigated, all but one were functional, providing high fundamental suppression without additional filtering. However, a certain output power and temperature sensitivity, together with a high chip-to-chip spread of the carrier suppression, has been observed. At moderate output power levels, about 90% of the devices provided sufficient carrier suppression at less than 1W of power consumption.