| Arbitrary waveform generator,as a signal source that can output user-defined waveforms,plays a vital role in testing fields.As the output stage of the arbitrary waveform generator,the conditioning channel affects various indicators of the final output signal.It’s very difficult to realize high analog bandwidth,wide amplitude dynamic range,high resolution and ultra-fast edge square wave due to the technical level and device performance.This thesis will design and implement a 5GHz bandwidth arbitrary waveform generator conditioning channel with two output modes of high bandwidth and high amplitude that based on the research of how to realize high bandwidth,high resolution wide dynamic range,high resolution DC bias,and ultra-fast-edge square waveform.The main research contents are as follows:1.Design of broadband amplifier circuit.For the amplification and conditioning of broadband signals,the performance of op-amps,gain blocks,variable gain amplifiers and differential amplifiers are analyzed based on the requirements of broadband conditioning capability,minimum swing rate,output power and differential output,and the full differential amplifier with the best slew rate and bandwidth is selected for the high bandwidth mode,and the op-amps with better output power is selected for the high amplitude mode.The LMH5401 and LMH3401 are used in the high-bandwidth mode where the LMH5401 is used to buffer the pre-stage DAC output and convert the single-ended signal to differential signal to meet the requirements of the post-stage circuit and the final output form,and the LMH3401 is used as the post-stage gain realization to meet the requirements of the output signal amplitude,and finally the mode with 5GHz bandwidth and 12 d B maximum gain is realized.In the high amplitude mode,a two-stage current feedback op-amp circuit is designed based on ADA4927 and THS3491 where ADA4927 is used for single-ended to differential conversion to meet the output requirements,and THS3491 is used as the high gain and high power realization to meet 5Vpp requirements in the high amplitude mode,and finally a mode with 370 MHz bandwidth and 15 d B gain is realized.2.Design of wide amplitude dynamic range and high resolution.For the problem of narrow dynamic range of input amplitude,an attenuation network with wide dynamic attention range and structure of the digitally controlled attenuator with bypassable fixed attenuator is designed after analyzing the operating frequency,attenuation range and insertion loss of various attenuation methods,the high bandwidth attenuation of the digitally controlled attenuator PE43704 B and the YAT fixed attenuator with 0.2d B insertion loss are selected.The structure realized 5GHz bandwidth with the maximum attenuation of-93 d B to meet the full bandwidth of the 35μVpp amplitude requirements.For the amplitude resolution of 50μVpp,the 16-bit DAC with voltage-controlled attenuator structure is designed based on the amplitude coarse adjustment and fine adjustment to increase the amplitude resolution from 1.38 m Vpp to 16μVpp.3.Design of ultra-fast-edge square wave conditioning circuit.Aiming at the problem that the rise time of the output square wave is too long(>300ps),a fast comparator with XOR logic gate structure is designed to output a square wave signal with a small enough edge time.At the same time,on the basis of avoiding deterioration of the output edge time of the logic gate,floating ground is set with the corresponding adjustment of the matching level of the front circuits to eliminate the DC bias contained in the output of the logic gate,so that the output signal meets the requirement that the rear conditioning circuit cannot contain the common-mode voltage.Aiming at the problem that the output square wave amplitude is not meet the standard,a differential amplifier circuit is designed after analyzing the spectrum characteristics of square wave to meet amplitude requirements of 1.5 Vpp in normal output amplitude mode.In order to meet the fast-edge square with a maximum amplitude of 5Vpp,a RF amplifier circuit is designed based on HMC8410 after analyzing the output characteristics like power.In order to lower the operating frequency of the RF amplifier,an integrated bias-tee network JEBT-4R2GW+ with lower operating frequency is used as the peripheral Bias-Tee circuit of HMC8410 to realize better low-frequency performance.Test results show that the designed conditioning channel realizes a real-time bandwidth of 5GHz(-8d B),an amplitude dynamic range of 35μVpp～1.5Vpp and a bias voltage range of-2.5V～+2.5V with amplitude and bias voltage resolution up to 16μV and 14μV.In addition,it can output ultra-fast-edge square wave with 47ps@1Vpp rise/fall time and 60ps@5Vpp high amplitude ultra-fast-edge square wave,and the comprehensive index is at the domestic leading level. |
