Abstract: According to the requirements of the modern electronic system and analytical instrument for the wind band, multi-frequency and small volume of the synthetic source, a new method for the synthesis of broadband is introduced. Based on PLL circuit with programmable logic control circuit, using multi-mode PLL(Phase Locked Loop) control circuit in the feedback divider ratio, so that the module, to achieve zero, a switch and a SPI(Serial Peripheral Interface) control modes, so as to obtain a single frequency, multi-frequency and wideband synthetic source three states respectively. Using Altera's CPLD(Complex Programmable Logic Device) to control the Hittite integrated PLL chip, obtaining the wideband synthetic source whose frequency range is 25 MHz ~6000 MHz and performance indicators reach the instrument level.