Background: One digitizer is used to implement a digital nuclear measurement for the acquisition of nuclear information. Purpose: A principle and method of a parameter-adjustable front-end controller is presented for the sake of reducing the quantitative errors while getting the maximum ENOB(effective number of bits) of ADC(analog-to-digital converter) during waveform digitizing

as well as reducing the losing counts. Methods: First of all

the quantitative relationship among the radiation count rate(n)

the amplitude of input signal(Vin)

the conversion scale of ADC(±V) and the amplification factor(A) was derived. Secondly

the hardware and software of the front-end controller were designed to fulfill matching the output of different detectors

adjusting the amplification linearly through the control of channel switching

and setting of digital potentiometer by CPLD(Complex Programmable Logic Device). Results:(1) Through the measurement of γ-ray of Am-241 under our digital nuclear measurement set-up with CZT detector

it was validated that the amplitude of output signal of detectors of RC feedback type could be amplified linearly with adjustable amplification by the front-end controller.(2) Through the measurement of X-ray spectrum of Fe-55 under our digital nuclear measurement set-up with Si-PIN detector

it was validated that the front-end controller was suitable for the switch resetting type detectors

by which high precision measurement under various count rates could be fulfilled. Conclusion: The principle and method of the parameter-adjustable front-end controller presented in this paper is correct and feasible.