John,

2N7002 is a small N-channel MOSFET.

Andy

I think it is a start-up problem, and that the feedback loop may have more than one stable operating point.? Without the capacitor, it comes up driving the MOSFET ON.? With the capacitor C4, it seems to start up with the MOSFET OFF (I don't know why the cap should make any difference for DC), and finds a stable operating point, with nothing to bring the MOSFET ON.? The op-amp's inverting input pin has the extra 10K resistor, and the input bias current of the op-amp seems to go up quite a lot when its inputs are both low, and this drives the op-amp's output low so it never turns ON the MOSFET.

I can't think of an obvious reason why C4 would affect that.? Maybe things are so very close to teetering either one way or the other, that the slightest change alters which way it goes.

You can change which "state" it comes up in, by adding an .IC statement.? That's why I think the circuit has multiple stable operating points.

Andy

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I can't imagine what this is supposed to do, even if it would run. Did you mean R7 to be 100 megohms?

A filter circuit simulation was offered in ABSE, uploaded as 45216607d4_puzzle.zip

If an output transient load section, or a component C4 is connected, the circuit
won't start. Gives miraculous ac filtering, when off, but curious to know the
simulator mechanics behind this odd effect in sim schematic.

RL

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Where is the 2N7002 in LTspice? I can't find it.

RL,

Please make sure to upload complete schematics including custom symbols.? Yours is missing a special custom symbol for the 2N7002.? (Why, I don't know.)

Andy

I think the "won't start" problem that RL refers to (without actually saying it), is that the output DC voltage does not come up.? The simulation runs, but the output voltage stays low (<1mV).

Roy, that is not what you see?

That is what I see when i used the 2N7002 symbol that comes with LTspice.? When C4 is removed, the output pops up to about 6V.

Andy

I replaced the missing Mosfet with another NMOS part.? The circuit starts up fine for me.

RL,

Please make sure to upload complete schematics including custom symbols.? Yours is missing a special custom symbol for the 2N7002.? (Why, I don't know.)

Andy

A filter circuit simulation was offered in ABSE, uploaded as 45216607d4_puzzle.zip

If an output transient load section, or a component C4 is connected, the circuit
won't start. Gives miraculous ac filtering, when off, but curious to know the
simulator mechanics behind this odd effect in sim schematic.

RL

On 02/03/2021 19:16, LV wrote:

I know about possibility for logic modelling in LTSpice...
But what if you need model 20000 gates?
Draw schematic in LTSpice?

I know this is an LTspice group, but I can't help thinking that for purely digital designs, you might be better off using a tool intended for such, like Logisim for example.

--
Regards,
Tony

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If you have a number of identical blocks of gates, there are two ways of defining one and automagically creating from it as many as you want, without drawing them all.

Hi Vlad
I know about possibility for logic modelling in LTSpice...
But what if you need model 20000 gates?
Draw schematic in LTSpice?

--
Best Regards
Victor

Victor wrote:

? ? "But what if you need model 20000 gates?
? ? ?Draw schematic in LTSpice?"

Is this still a question about reversible logic?? (If it isn't, please start a new Topic.)

LTspice can simulate many thousands of gates.? It has been done with tens of thousands, if not hundreds of thousands.? It is limited by your computer's memory, not by LTspice.? Using LTspice's built-in A-devices instead of full transistor-level circuits should make it both more compact and faster.

Obviously, one may want to use hierarchy (subcircuits) when doing thousands of gates.? Right?

Andy

Hi Vlad
I know about possibility for logic modelling in LTSpice...
But what if you need model 20000 gates?
Draw schematic in LTSpice?

--
Best Regards
Victor

Hello LV

You need study HDL (VHDL or Verilog) and use appropriate tools like Modelsim
or Active HDL

The gates have a truth table that can be easily implemented in LTspice
with A devices or .MACH. The only things to take care of are the
transition times, since LTspice is a SPICE and, thus, an analog
simulator: it will consider everything, not just the before/after
states, which means there may be occasional spikes, that's all.

--
Vlad
______________________
ltspicegoodies.ltwiki.org v2:
quite universal analog/digital filter,
power electronics, signal processing,
easy to work with math functions,
digital models, and rants.

Hello
You need study HDL (VHDL or Verilog) and use appropriate tools like Modelsim or Active HDL
--
Best Regards
Victor

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A web search indicates that reversible gates can be made from logic that has 3 inputs and 3 outputs. These can be built in LTspice, using the special A-devices or perhaps even with real parts. But LTspice is an analog simulator, with somewhat limited application to pure digital circuits.

Aditya wrote, "I wanted to know if it is possible to implement reversible logic gates like "Toffoli" and "Feynman" in LTSpice."

LTspice (note the spelling, the 's' is not capitalized) is an electronic circuit simulator.

If you have a circuit that can be built using transistors, diodes, resistors, capacitors, inductors, and if you have SPICE models for the semiconductor parts, it can be simulated in LTspice.? It can even simulate circuits that have some other components (valves or vacuum or thermionic tubes) or some imagined devices described mathematically (controlled sources, or math functions).

Do you have a real electronic circuit for the kind of logic gates you want to simulate?? Then it can probably be simulated in LTspice.? If there is no real functional equivalent for the thing you want, then maybe, or maybe not.

Now it's your job to see if there are SPICE models for these devices.

Andy

Aditya wrote, "I wanted to know if it is possible to implement reversible logic gates like "Toffoli" and "Feynman" in LTSpice."

LTspice (note the spelling, the 's' is not capitalized) is an electronic circuit simulator.

If you have a circuit that can be built using transistors, diodes, resistors, capacitors, inductors, and if you have SPICE models for the semiconductor parts, it can be simulated in LTspice.? It can even simulate circuits that have some other components (valves or vacuum or thermionic tubes) or some imagined devices described mathematically (controlled sources, or math functions).

Do you have a real electronic circuit for the kind of logic gates you want to simulate?? Then it can probably be simulated in LTspice.? If there is no real functional equivalent for the thing you want, then maybe, or maybe not.

Now it's your job to see if there are SPICE models for these devices.

Andy

I am new to reversible computing and reversible logic in general. I wanted to know if it is possible to implement reversible logic gates like "Toffoli" and "Feynman" in LTSpice. Any help would be really appreciated.
Thank you.
Aditya

The ADHV4702 is a small signal op amp with operation to 220V and 10MHz GBW. Add an HV current buffer, schematic same as LH0002 and you are set. You'll have to chase down some HV NON and PNP devices as the LTspice library only goes to 150V. And you will likely need a heat sink if there is more than 1mA or so load current.

Will do. Just thought I'd check to see if it's a known bug before assembling the stuff.

dcorner1953 wrote, "LT refuses to bring up the current meter or thermometer icons for just two components in the entire circuit"

Just to be clear, transistors have 3+ terminals, so the currents you're talking about are their pin currents.? You can't measure (plot) the current on a transistor, but you can plot the current into each pin.? Make sure to position the pointer on the wire going to that pin, otherwise the current meter won't appear.

If the transistor model is a .SUBCKT model, you should enable saving subcircuit currents.? That setting is in the Control Panel, Save Defaults tab.? Also, if you used a .SAVE or .PLOT or .PRINT command anywhere on your schematic, those commands limit what voltages and currents are saved, so don't use them unless you really need them.

It is not a known bug.? Certainly nothing that affects transistors in the upper left quadrant of your schematic -- or the upper left I/V quadrant -- or the upper left quadrant of the bridge -- or whatever else you meant.

? ? "What other surprises might LT have in store for this circuit?"

Well, for one thing, the values you used for R34 and L2 are ridiculous, so don't use those!? Also, your 2N3055 might need to be reconsidered.? And don't use a 1N34 as the power rectifiers!? You knew that, right?

? ? "Seems LT glitched something in the original file, but how did copying do a partial fix?"

Isn't it obvious?? When you did that copy, the moon eclipsed Mercury and that rearranged all the charm quarks in the copied version.? I could tell by looking at your schematic, it was as plain as day.

:-)

Now where did you put that schematic?? Oh, wait, you didn't!? I guess my mind-reading skills need a little work.

Stop trying to make us guess what's in your schematic.? Upload it.

Andy