proper way to connect single ended to differential circuits - Page 1
Forum section: electronics / projects

author: john23
author_rank: Frequent Contributor
timestamp: February 23, 2025, 12:25:30 pm
content: Hello , I have a single ended PID and a vccs driver (differential )What is the best way to connect the two, so the PID output will be driver input?Thanks.

author: Zero999
author_rank: Super Contributor
timestamp: February 23, 2025, 01:05:01 pm
content: The first schematic doesn't make any sense. Are those boxes supposed to be op-amps? LTSpice has its own op-amp symbol for use with any model. It's in the op-amps section of the component selector and is called opamp2. Please use it, rather than meaningless boxes.You can easily make the output differential by adding an inverting amplifier with a gain of 1 to the output.

author: john23
author_rank: Frequent Contributor
timestamp: February 23, 2025, 01:24:44 pm
content: Helo Zero999, Yes I try to learn how to present my opamp in a OPAMP2 manner.I am learning from videos like the one shown below.The problem Is that I dont my convertion ruin the functionality .The first circuit is a PID controller,which some AC responce.What component you reccomend me to use so this functionality wont get hurt?Thanks.Ltspice files are attached.

author: Zero999
author_rank: Super Contributor
timestamp: February 23, 2025, 02:38:30 pm
content: I downloaded the AD797 model from the Analog website. Opened it in a text editor and copied and pasted it into a spice directive on the schematic.I noticed there's an extra decompensation connection, which you're not using, so I removed it. If you were using it, the solution would have been to use another op-amp symbol with another connection for decompensation or whatever. The netlist order for the AD797 subcircuit is the same as opamp2 so nothing else needed to be changed. I configured the AD797 as an inverting amplifier, as per the application schematic in the data sheet.https://www.analog.com/media/en/technical-documentation/data-sheets/ad797.pdfHere's the .asc file.You can copy and paste the SPICE directive and the AD797 into your schematic. You just need an inverting amplifier on the output to give you a differential output.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: February 23, 2025, 03:27:45 pm
content: Quote from: john23 on February 23, 2025, 12:25:30 pmTo answer the narrow question, how to convert a single-ended signal to differential, you can use voltage-controlled voltage sources, E.Here are two examples:In the left example the output of E1 is floating, it is reference to ground by the resistors R6 and R7.In the right example the outputs are ground referenced. They are offset from ground by a common mode voltage.The voltage-controlled voltage sources are ideal components, they do not introduce phase shift. The parameter sets the gain.Regards,Jay_Diddy_B

author: john23
author_rank: Frequent Contributor
timestamp: February 23, 2025, 08:07:53 pm
content: Hello, I tried to put on input of the differential circuit to GND and the other input to the output of the PID.but its not working as you can see in the attached photos.Its as if my PID output is dead.Where did i go wrong?LTspice file is attached.Thanks.

author: Zero999
author_rank: Super Contributor
timestamp: February 23, 2025, 08:38:09 pm
content: What the heck is that circuit supposed to do?It looks as though the inverting and non-inverting and inverting inputs are transposed.U1 has no DC negative feedback path.Here's a schematic which corrects the obvious faults but that peak on the AC plot indicates it'll oscillate.And why are there three inverting amplifiers with different gains in parallel?

author: john23
author_rank: Frequent Contributor
timestamp: March 03, 2025, 05:36:24 pm
content: Hello Zero999, I am building a PID controller .As you can see from the photos and simulation file , the pulse input turns into ramp in integrator and two pulses in differentiator.Regarding connecting the ADSL driver to the PID controller.Could you say what is the logic how properly its suppose to be done?I could not understand the logic in the extra opamp configuration you did.Thanks.