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RF Signal Generator Based on Time-to-Analog Converter in 0.18 µm Complementary Metal Oxide Semiconductor

In this paper, we propose an inductorless scalable RF signal generator from a digital pulse signal. Conventionally, digital-to-analog converters (DACs) generate analog signals by summing quantized voltage steps digitally. However, the DACs are not suitable for low-voltage operation in the fine complementary metal oxide semiconductor (CMOS) IC because the required quantized step becomes smaller as the CMOS process becomes finer. To overcome this, a time-to-analog conversion technique is suggested. The suggested circuit can advance the time step resolution and the low-voltage operation is possible. A prototypal time-to-analog circuit that generates sinusoidal waveforms from digital RF input was fabricated using 0.18-µm CMOS technology. The frequency was 128 MHz and the output power was -6.6 dBm. The output levels of the second and third harmonics were -23 and -37 dBc, respectively. The time-to-analog conversion technology suggested could become more attractive in the future if finer CMOS technologies that can realize higher time resolution are applied.