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Hello,
I just came across CIRCUIT060046: "High-side V-I with bipolar junction transistor (BJT) circuit"
I noticed that the description reads "This low-side voltage-to-current (V-I) converter delivers a well-regulated current to a load..."
I wonder what to call this circuit correctly: a high-side load or a low-side switch circuit?
Anyhow, there's a design document available for this circuit, SBOA325. Page 3 reproduces the results of an DC as well as an AC analysis run using Tina-TI.
I downloaded the model and could re-generate the "DC Simulation Results" as shown in SBOA325.
However, I failed to re-generate the "AC Simulation Results". The AC analysis results look rather strange:
What am I doing wrong? I guess I have to manually add the proper curves using the post-processor feature.
Please advise.
Thanks.
Dan
Hey Daniel,
To collect open loop data, you will need to open the feedback loop of the amplifier. However, where to break the loop can be tricky, but there is a method that works reliably.
This output gives you the loaded Aol (aol-beta) from the AC simulation.
Best,
Jerry
Thanks for your reply. I changed my circuit accordingly and now I get the same results as you do:
I have some follow-up questions
Almost exactly the same curve. Although, I did not add the negative power supply Vee. How relevant is that?
Further what exactly is this circuit below doing? I think I have seen it before but I don't really grasp all the details of it:
This is my understanding of this circuit: The inputs to the op amp are split into "IN+" and "(IN+)" (respectively for negative input) to break the feedback loop. Source Vi is AC coupled only (via C5) to the inputs of op amp "IN+" and "IN-". Feedback loop "(IN-)" and reference signal "(IN+)" are connected to the meter VM1.
Why are L1 and L2 required? They seem to provide a DC only path between the inputs that have been split up. However, without L1 and L2 the AC analysis does not produce a result.
Why are C2, C3, C4 required? Without them I still see a result but it changes drastically.
Further, our simulation results in a 0 db point at 8 MHz with a phase margin of +60°. The SBOA325 reports a phase margin of +78° at 237 kHz. Why is this?
Thanks a lot
Best regards,
Dan
PS: Below is my Tina TI file attached.
Hey Daniel,
Best,
Jerry
Hello Gerasimos Madalvanos,
Your thorough answer is very helpful. Thanks.
I found your decoupling circuit also in other answers here in amplifier forum and Vi/VM1 are connected as you did.
However, I just noticed that I "mounted" the voltage generator Vi and the voltage meter VM1 in reverse polarity compared to your decoupling circuit.Does that make any difference? I think it should not as I connected both the other way round.
Thanks.
Dan
Hey Daniel,
I don't believe it would make a difference, as the large capacitor creates an AC short between the two inputs anyways, so the difference would just be the polarity of the input relative to the polarity of the voltage meter, as long as those are kept the same, it should be okay.
Unsure if there are other repercussions but at first glance it seems ok.
Best,
Jerry