地球物理勘探用高精度隔离放大器

地球物理勘探在野外进行,测量的电信号振幅范围为n×100 uV～ n×1 V, 对电信号测量精度要求优于0.1%.这就要求相应的隔离放大器增益范围大,档差小, 温漂小.为了满足上述要求,设计的精密隔离放大器由高线性度高精度器件-隔离放大芯片AD202-组成隔离级,3个零漂移运放LT1250组成3级9档放大级,档差为10 dB,增益从0～ 90 dB可控.实际电路的测试结果表明: 基于AD202和LT1250设计的隔离放大器的最大非线性误差为0.23%,19小时内的漂移为27 uV,达到了设计要求.

High precision isolation amplification instrument for geophysical exploration

A high precision isolation amplifier for front-end electrical filed conditioning and sampled current signal isolation amplification is introduced. The instrument is composed of the input buffer circuit, the first stage amplifier and the low-pass filter with gain as 0 dB, 10 dB, 20 dB, 30 dB, the second stage amplifier and the low-pass filter with gain as 0 dB, 10 dB, 20 dB, 30 dB, the third stage amplifier and the low-pass filter with gain as 0 dB, 10 dB, 20 dB, 30 dB, the isolation stage with high linearity, high precision isolation amplifier AD202, the output stage with low-pass filter, gain control circuit, and overload detection and indication circuit. It offers a total gain the 90 dB; ensures proper amplification of small signal less than 100 uV. To test the instrument, the small signal input test, the frequency response test, and the non-linearity test and drift test are carried out. Test results show that the maximum nonlinear error of the isolation amplifier based on AD202 and LT1250 is 0.23%. Its drift is 37 uV in 19 hours, reacheing the requirement of the design.