Design of Low-Cost Ground Penetrating Radar Receiving Circuit Based on Equivalent Sampling

Abstract

Based on the principle of equivalent sampling, a low-cost ultra-wideband ground penetrating radar (GPR) receiving circuit is proposed in this paper. The circuit is mainly composed of three parts: high-precision delay control circuit, sampling pulse generating circuit and equivalent sampling circuit. The Step-Recovary Diode(SRD) and the avalanche transistor are used to generate the sampling pulse signal, and the step recovery diode is used as the front sharpening circuit to drive the avalanche transistor. As a result, a sampling pulse signal with a bottom pulse width of about 430 ps and an amplitude of up to 1.5 V is generated. RF transistors are used in the equivalent sampling circuit to obtain a new triode equivalent sampling circuit which replaces a complex diode bridge circuit with a triode. The equivalent sampling circuit is verified by using a 2ns, 500mV triangular wave as the sampled signal. After being sampled and held, the signal is stepped, and each sampling point corresponds to the signal to be taken, and the holding time is 100 ns. In the time domain, the ultrawideband pulse waveform is stretched by a factor of 1000, and the relative sampling frequency is reduced by a factor of 1000. Meanwhile, at the same time, the original pulse width of 2ns becomes a 2us waveform. Through the equivalent sampling method, the receiving circuit can post-process the sampled signal by using an ADC with a low sampling frequency and a low price. The equivalent sampling method solves the problem of dependence on ultra-high-speed A/D chips and greatly reduces the hardware cost of system design.