A 26GHz-Band Image Enhancement Type 1-Bit DAC for Direct Digital RF Modulator

In this paper, we propose an image enhancement type 1-bit digital to analog converter (DAC) for the direct digital RF modulator. The direct digital RF modulator is a technique to directly generate the RF signal by the 1-bit bandpass (BP) Delta-Sigma $(\Delta\Sigma)$ modulator using the image signal. The proposed 1-bit DAC is attached to the output of the 1-bit BP $\Delta\Sigma$ modulator and is able to enhance the higher-order image signal power and its SNR. We have designed and fabricated a 26GHz-band image enhancement type 1-bit DAC IC in 65nm CMOS process. The fabricated 1-bit DAC amplifies the higher-order image signals of the output signal of the 1-bit modulator, but also generates the higher-order images from the lower signal components of the modulator output. As the result, the proposed DAC improves the 26GHz output power of 4.6dB and SNR of 6.1dB in the case of 1.2Vp-p/8Gbps Manchester coding 1-bit data stream.