The Design Of Arbitrary Waveform Generator Conditioning Channel With 4GHz Bandwidth

The high-bandwidth arbitrary waveform generator has important application value in many fields such as industry and military.The arbitrary waveform generator conditioning channel is used as the output end of the instrument,which determines the instrument's analog bandwidth,output amplitude,and waveform purity.Therefore,the research on the conditioning channel of the arbitrary waveform generator is of great significance.To achieve 4GHz bandwidth arbitrary waveform generator conditioning channel,the article primarily did the following work:1.Realize high waveform purity of the output signal.The spectrum characteristics of the input signal of the conditioning channel module are analyzed,and the conclusion that the output signal contains thenf_s?f_o image frequency component is obtained.For the image frequency spurs,the LTCC low-pass filter is used to design the pre-stage filter circuit.Aiming at the harmonic noise introduced by active devices such as amplifiers in the conditioning channel,the filtering network is segmented,and high-bandwidth switching devices and LTCC low-pass filters with different cutoff frequencies are used to design a multi-stage filtering circuit.Finally,the spurious-free dynamic range index of up to-60dBc in the DC~4GHz band is achieved.2.Realize broadband signal amplitude conditioning.The amplitude characteristics of the input signal of the conditioning channel module are analyzed,and the conclusion that the input voltage range is 200mVpp~936mVpp is obtained.Combined with the amplitude index of a certain type of 4GHz bandwidth arbitrary waveform generator,the amplitude interval division design was carried out.Using high bandwidth switching devices and the same series of fixed attenuators with different attenuation values,a multi-stage attenuation circuit is designed.To achieve broadband signal amplification,a fully differential amplifier is used in the low frequency band(less than 1 GHz);and an RF amplifier is used in the high frequency band(more than 1 GHz).Finally,the range of40mVpp~2Vpp differential output within the DC~4GHz band is achieved.3.Realize broadband DC offset adjustment and ultra-fast square wave.In order to achieve broadband DC offset adjustment,in the low frequency band(less than 1GHz),the resistance plus bias scheme is used;in the high frequency band(more than 1GHz),the bias tee is used for offset adjustment.In response to the requirements of the offset circuit and the square wave conditioning circuit for the offset voltage source,a low-speed voltage output DAC,an eight-channel analog multiplexer and a general-purpose operational amplifier,combined with FPGA control,realize an independently controllable,eight-channel output Offset voltage source with a voltage above±10V.In the end,the DC offset voltage in the DC~4GHz band reaches±0.5V,and the offset voltage resolution reaches 10mV.In response to the demand for ultra-fast edge square waves,a high-speed XOR logic gate device is innovatively adopted,and the output amplitude is adjusted through the VR pin to finally realize a square wave with a controllable rise/fall time of less than 90ps.4.Signal integrity design.Clarified the necessity of signal integrity for 4GHz bandwidth circuit design.Aiming at the problem of extreme loss in the fully differential signal chain,the coupling and impedance of the differential transmission line are analyzed.Weakly coupled differential wiring with a line spacing greater than 3 times the line width and uncovered solder resist ink is used.Aiming at the problem of impedance mutation of signal vias,the parasitic parameters of vias are analyzed.Via design that reduces via diameter and pad diameter,increases anti-pad diameter,and provides proper grounding vias are used to improve via impedance discontinuity.Finally,a low-distortion,high-impedance conditioning channel circuit is realized.The system test results show that the conditioning channel module designed and implemented for a certain 4GHz bandwidth arbitrary waveform generator in this paper is capable of amplifying,attenuating,offsetting and filtering multiple waveforms such as sine wave,square wave and arbitrary wave output from the previous-stage waveform synthesis module.The conditioning channel module can realize the differential output amplitude dynamic range of 40mVpp~2Vpp within the 4GHz bandwidth,realize the DC offset adjustment of offset voltage of±0.5V and resolution of 10mV,and achieve the highest spurious-free dynamic range of less than-60dBc Signal quality indicators.