Design And Research Of Frequency To Voltage Conversion Module Based On LTCC Technology

Recent years,with the development of hybrid integrated circuit technology and aviation technology,military avionics require more and more performance and reliability.In the airborne flight instrument system,some signals can’t be measured directly,so they need to be converted to be displayed in the instrument.Meanwhile,high stability of the system is required,and the conversion module is characterized by miniaturization.At present,this is a trend in the field of aerospace development and one of the hot spots and key points of research.Frequency voltage conversion module is an important part of airborne flight instrument system,which converts the sine wave signal with fixed amplitude into dc voltage signal.Most of the signal conversion is linear,and the substrate is Printed circuit boards(PCB).However,in practical engineering applications,the output is required to be piecewise linear and the volume is smaller.Aiming at this requirement,this paper designs a frequency voltage conversion module with piecewise linear output,and uses low temperature co-ceramic technology(LTCC)to greatly reduce the area of the circuit board,so as to achieve module miniaturization.The whole circuit is divided into four parts:DC-DC power conversion circuit,voltage comparison circuit,frequency voltage conversion circuit and analog switching circuit.Then the chip selection in the circuit is carried out through theoretical analysis,and the resistance value and capacitance value are determined.Then the baseboard of the frequency voltage conversion module is designed referring to the LTCC design specification including the selection of layers and the layout of each layer,the choice of chip,capacitor and resistance package,and the design of square resistance.Next,the design of cavity and cover was completed according to the size of LTCC substrate,and the LTCC substrate was glued to the cavity.Finally,using the cover to seal the module to complete the entire work from design to production with a weight of only 25g,a size of 22.6×14.6×4.5mm.After the completion of the frequency voltage conversion module,the electric performance test is carried out on it.When the input sinusoidal signal with fixed amplitude of 500mVpp and frequency of 0Hz～1685Hz,the output dc voltage is 0.5v～4.5v after conversion.When the frequency is from 0 to 85Hz,the output dc voltage of 0.5v is stable,and when the frequency is from 85Hz to 1685Hz,the output voltage of 0.5v to 4.5v is linear.The output voltage conversion error is≤±10mV at 25℃,≤±20mV at-55℃ and 125℃,which meets the technical index requirements.At the same time,the environmental test was carried out on the module,and the test results were qualified.It is able to adapt to the harsh airborne environment,with high precision,high reliability,good stability and small volume.