| Frequency counter is a commonly used electronic measurement and analysis instrument.At the same time,it is also an important instrument to measure frequency,cycle and time interval in the research field of electronic measurement and instrumentation research.One of the keys to developing high-accuracy frequency counter is to design an analog channel with low noise,high bandwidth,and high dynamic range.In this thesis,according to the requirements of the design index,the appropriate discrete components are selected to complete the construction of the analog channel circuit of the frequency counter,and the localization of the components is realized.The main research contents of this thesis are as follows:1.Research on high precision broadband signal compensation bias circuit.Aiming at enhancing the driving ability of the circuit,a common drain electrode-common collector amplifier circuit is designed by using FET and triode;In order to meet the bandwidth requirements of 1GHz,by comparing different design schemes,analyzing the circuit structure,a broadband signal compensation bias circuit is designed.Finally,the actual circuit is built and debugged with discrete devices.2.Design of trigger circuit of comparator.In order to meet the requirements of low propagation delay and strong anti-interference ability,a high-speed comparator is used to shape the signal through hysteresis comparison;for the trigger voltage requirement of the analog channel,a dual-channel voltage output DAC is used,and the DAC is configured as bipolar The output,combined with FPGA control,the trigger level can be changed arbitrarily,achieving a voltage resolution of 3m V and the trigger voltage range covering-2.5V～2.5V.3.Localization and substitution of analog channel devices.The construction of the analog channel circuit of the entire frequency counter is completed by selecting appropriate discrete devices,and on the basis of the existing product technology,by comparing the index parameters of different devices,the circuit debugging work is continuously carried out,and the analog channel of the frequency counter is used.The device has achieved localization substitution and improved independent controllability.4.Design of analog channel digital logic.In order to complete the conditioning of the input signal,a digital logic is designed to control the analog channel quickly and efficiently through FPGA;according to the requirements of the signal parameter measurement function,the design logic makes the DAC output analog voltage change step by step with the input signal,and realizes the high-speed comparator and signal parameter measurement with variable duty cycle to improve the functional completeness of frequency counters.Finally,the entire analog channel of the frequency counter is tested and verified by building a test platform,and the key indicators such as input impedance,input voltage dynamic range,bandwidth,and voltage resolution of the analog channel are tested,and the test results all meet the design requirements. |
