对数放大器提高A/D转换器动态范围的研究

Studies of Logarithmic Amplifier Enhancing Dynamic Range of A/D Translator

A/D转换器可以将模拟信号转换为数字信号,供计算机进一步处理,在各类自动化过程控制以及仪器仪表中应用广泛,不同的应用对A/D转换器的参数要求不一样,在一定的转换精度要求下,对大动态的模拟信号进行转换要求A/D的分辨率较高,即位数较高,这在有些场合是不经济的,甚至是不可实现的.将大动态的输入信号先进行对数放大,得到压缩的较小的输出动态,再加到A/D转换器进行量化,可在不增加A/D位数的情况下处理大动态的输入信号.一个实际可实现的对数放大器,在进行小信号处理时,必然偏离真正的对数,设计对数放大器时应考虑其线性一对数过渡.对小信号时出现的平方律检波导致对数变换时多出的乘2因子可利用增益调整进行消除.

A/D translator can convert analog signals into digital signals for computers to give further treatment, which has widely been used in all kinds of automation procedure control and apparatus. Different usages lead to different parametric requirements of A/D translator. According to certain conversion ac- curacy , transferring main wire dynamic analog signals requires a high distinguishability of A/D, i.e. , a high digit, which is not economic in some occa- sions, even unrealized. First carry logarithm amplify to main wire dynamic input signals, and achieve minor necked output dynamic state, then add to A/D translator in order to quantify ; therefore, main ~5re dynamic input signals can be treated without the augment of digits of A/D translator. During the disposal of minor signals, a practical logarithmic amplifier will deviate necessarily the real logarithm, therefore the linearity logarithm transition should be consid- ered when designing logarithmic amplifier. Square law rectification occurred in the disposal of minor signals will lead to extra factor multiplied by two in log- arithm conversion which can be canceled by gain adjustment.