A low distortion wide band CMOS direct digital RF amplitude modulator

In English This paper describes a low distortion wide band CMOS direct digital RF amplitude modulator, which uses a 10-bit linear interpolation current steering digital to analog converter (DAC) and a Gilbert cell based mixer to generate an amplitude modulated RF signal directly. The linear interpolation increases the attenuation of the DAC's image components. The low pass filter (LPF) is therefore eliminated, and the RF transmitter structure is simplified. This modulator is suitable for system-on-chip design. The chip has been fabricated in a 0.35 μm, 3.3 V digital CMOS process. When the transmission signal is at 3 MHz, the distortion components are below -54 dBc at 800 MHz and -49 dBc at 1.2 GHz, respectively. The image signals are below -45 dBc when the transmission signal is 5.2 MHz