原创 单端输入与差分输入的区别(中英文)

1、Single-Ended Signals/Inputs<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

Single-ended inputs connect one wire from each signal source to the data acquisition system. The data acquisition system then simply measures the difference between the signal and the ground (or earth) at the PC. This requires that the signal source is grounded (earthed), and is the same value as that at the PC.

2、Differential Signals/Inputs

Differential inputs use two signal wires from each signal source to the data acquisition system. One connected to the positive input and one to the negative input. The voltage between the input and the PC ground is monitored by two high-impedance amplifiers. A third amplifier is used to measure the difference between the +ve and -ve inputs, eliminating any voltage common to both wires. This method eliminates the problems that can occur with a single-ended system. That is any differences in grounds are irrelevant, and noise can be reduced; using twisted pairs ensures that any noise generated will be the same for each wire.

3、Pseudo-differential Inputs

Some data acquisition boards claim to be differential but are in fact pseudo-differential inputs. This is acceptable provided the signal sources are close together and do share a true common ground. Pseudo-differential is similar to single-ended with the ground of the signal isolated from the PC. The source ground is then connected to the PC ground, by measuring the difference between these two grounds; the effect of this difference can be removed from the measurement. However, pseudo-differential inputs can not eliminate the effects of noise. Choosing between single-ended and differential inputs, differential is best when signal leads are over a few meters in length. This eliminates the effects of noise pick up and the possibility of ground differentials. Measuring small signals under around 100 mV, these can be overwhelmed noise and ground differentials. Measuring output from sensors with high impedance such as strain gauges, differential inputs remove common mode voltage. High impedance can lead to higher common mode voltages. Single ended is appropriate - When you want a low cost system to measure a lot of input signals and you are confident that the above situations can be eliminated.

4、单端输入与差分输入简介

单端输入，输入信号均以共同的地线为基准。这种输入方法主要应用于输入信号电压较高(高于1 V)，信号源到模拟输入硬件的导线较短(低于15 feet)，且所有的输入信号共用一个基准地线。如果信号达不到这些标准，此时应该用差分输入。对于差分输入，每一个输入信号都有自有的基准地线。由于共模噪声可以被导线所消除，所以差分输入可以减小噪声误差。

单端输入时, 是判断信号与 GND 的电压差；差分输入时, 是判断两个信号线的电压差。对于差分输入，当信号受干扰时, 差分的两线会同时受影响, 但电压差变化不大，因此差分输入方式的抗干扰性能较佳。而单端输入的一线变化时，由于GND不变, 所以电压差变化较大，因此单端输入的抗干扰性能较差。

5、差分走线的优势

差分信号和普通的单端信号走线相比，最明显的优势体现在以下三个方面：

(1) 抗干扰能力强，因为两根差分走线之间的耦合很好，当外界存在噪声干扰时，几乎是同时被耦合到两条线上，而接收端关心的只是两信号的差值，所以外界的共模噪声可以被完全抵消。

(2) 能有效抑制EMI，同样的道理，由于两根信号的极性相反，他们对外辐射的电磁场可以相互抵消，耦合的越紧密，泄放到外界的电磁能量越少。

(3) 时序定位精确，由于差分信号的开关变化是位于两个信号的交点，而不像普通单端信号依靠高低两个阈值电压判断，因而受工艺，温度的影响小，能降低时序上的误差，同时也更适合于低幅度信号的电路。目前流行的LVDS（low voltage differential signaling）就是指这种小振幅差分信号技术。