Design Of Acousto-optic Tunable Filter Multi-channels Drive

A new Acousto-Optic Tunable Filter (AOTF) multi-channels drive based onDirect Digital Synthesizer (DDS) is presented in this paper, to improve theperformance of the Sound-light tunable filter. The drive using a new generation DDSchip AD9959and controlled by FPGA, which can provide independent frequencyoutput on four channels, each channel of AD9959is controlled by the program ofFPGA. The program can be used to correct unbalances between signals due toexternal reason. The FPGA control program is written in Verilog HardwareDescription Language, with a method of synchronous finite state machine (FSM), toachieve the function of receiving external control data and sending control data toAD9959.The power of signal of producing by AD9959is limited and can`t meet therequirements of driving the AOTF crystal, so we must amplify the signal by the linearpower amplifier circuit, and then the signal can drive the AOTF crystal. Themulti-stage cascade is used to realize high linearity and high gain in the poweramplifying module. In the first stage, digital variable gain amplifier is used to achievethe output power adjustable. The power amplifier circuit is a super broadbandamplifier. To avoid the lack of matching of capacitance and inductance, so we usemicro strip line and transmission line transformer for impedance matching design,furthermore, this impedance matching design can expand the bandwidth, and enhanceanti-interference ability of the circuit, thus keeping the purity of drive signal. TheAOTF drive designed in paper can realize RF signal output of the frequency range of65MHz-225MHz, and resolution of0.1Hz. The power and purity of signal meet thedrive requirements of AOTF, thereby achieving high-precision spectral scanning ofthe AOTF spectrometer in the range of400-1000nm.