I am trying to make an analog isolator of my own. The isolator needs to isolate analog signals (0-10 V) and should have relatively high bandwidth (up to 1 MHz) with unity gain. I am a beginner as far as electronics are concerned.
I found a design on the internet from Stanford research systems. The design looks great (input signal -10 to 10 V and up to 1 MHz bandwidth with unity to x100 gain) but I am puzzled by some of the components:
The schematics I found (https://xdevs.com/doc/Stanford_Research_Systems/SIM900/sim984_sch.pdf) contain three pages, the first page is the interfacing electronics, the second is the actual isolation electronics, the third is the power supply electronics. I am mainly interested in the second page below:
Again you can find the complete schematics here: https://xdevs.com/doc/Stanford_Research_Systems/SIM900/sim984_sch.pdf
First, the basics of the design (from the device's manual (https://www.thinksrs.com/downloads/pdfs/manuals/SIM984m.pdf)):
*The upper portion of Page 2 shows the floating input amplifier. Gain is controlled through latching relays U214 and U215, the control coils of which are earth-referenced.
*The (amplified) signal is optically coupled through U205, U206, U207, and U208.
*The (earth-referenced) output circuitry includes the output bandwidth control. This circuitry is on the lower portion of Page 2 of the schematics. The overall AC gain is trimmed using VR202 at the factory, and should not require user adjustment.
*DC offset can be adjusted with VR203, accessed from the front panel of the instrument. Note that the offset trim is referenced to the output, and comes after the gain is applied
What are the components in the purple frames, and in the bottom left light green frame doing ? These ICs don't even seem to be connected to any part of the circuit except the ground and the power supplies.