Need analog optical isolator

Thread Starter


Joined Jun 1, 2006
Iam presently working with designing an 8 channel analog input card ( This is one of the I/O modules of a control system).

I am using a optical isolator IL300D an analog optical isolator from Vishay electronics. the signal after isolation goes to the 8X1 mux and then to the input of a 16 bit ADC. After conversion the out put is varying much frequently , i could almost get stability in the MSB 2 niblles only, the lSB 2 nibblesare varying erratically. The return paths for my input signal is the ground before the optical isolator. I doubt that as the channel return path and the gnd are same, due to surges or ripples in the ground plane which is more likely in a circuit comprising of mixed signals the voltage level of the return is varying frequently. Iam enclosing the cicuit also. Iam enclosing the signal conditioning circuit which starts at the input to the card and terminates before the 8X1 MUX. The input range (0-5v) or (4-20)mA. could anyone solve my problem or suggest an analog optical isolator and preferably a working circuit built with it along with input and output specifications.


Joined Jan 28, 2005
Hi saha,

I took a look at the datasheet for the IL300 device and in it I found a typical hookup for the device (see figure 1 on page 2). I noticed a couple of significant differences between the one shown figure 1 and the hookup that you provided in your post. For example, in your schematic the opamp stage driving the optical emitter has the emitter referenced to +15V. In figure 1 of the datasheet, the optical emitter is is referenced to ground.

You may want to consider reconfiguring your connections to the IL300D to be like the one shown in the datasheet figure to see if that solves your signal stability problem.

IL300 Datasheet