Design and Implementation of Ultrafast Broadband Sweep Source based on AD9914

Abstract

To address a technical difficulty of long scanning cycle of broadband (100 MHz~900 MHz) frequency sweep source, an ultrafast broadband sweep source was designed based on the basic principle of direct digital-frequency synthesis (DDS) theory by using the high-performance DDS chip AD9914. During the design, the DSP28335 chip was used as the control device. The designed source can output 100MHz~900 MHz swept-frequency signals and it can realize sawtooth wave frequency-modulated signals in the shortest cycle (8us) by configuring the digital ramp generator in the chip. Moreover, a microstrip stepped impedance low-pass filter was designed using ADS to eliminate spurious signals in the direct synthesizer and decrease the in-band attenuation, thus making the curve flatter. According to final test and experimental data analysis, the designed sweep source has a large output broadband, short sweeping cycle and strong inhibition of spurious signals. It possesses great application values.