开云体育

  1. LTspice
  2. Messages
Expanded Topics Messages Polls
Date
Re: Creating a dirt-simple subcircuit component

 

There are dynamic range issues with very small resistors.
?
Pre-LTspice, I saw simulations with very small resistors where voltages drifted a few volts beyond the supply rails.
?
Andy
?
Re: Creating a dirt-simple subcircuit component

 

On Sun, Apr 13, 2025 at 04:11 PM, John Woodgate wrote:

Why not?

On 2025-04-13 23:58, eetech00 via groups.io wrote:
I don't recommend the use of tiny valued resistor as jumpers.
?
Because a zero valued voltage sources' behavior is basically transparent to the simulator.
A small valued resistor in not. It still exhibits behavior in the circuit as resistor and could
affect high frequency simulations or behavior of models that contain tiny valued parasitic components.
Re: AC Analysis - show Mag in dBuV versus Freuqncy

 

开云体育

dBu? is decibels referred to 0.775 V, which is 1 mW in 600 ohms. dB?V, or better dB(?V), is decibels referred to 1?V.

On 2025-04-14 00:02, Zivko Petru via groups.io wrote:
?
dbu on the other hand is referenced to 1 uV.
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only If something is true: * as far as we know - it's science *for certain - it's mathematics *unquestionably - it's religion

Virus-free.
Re: Creating a dirt-simple subcircuit component

 

开云体育

Why not?

On 2025-04-13 23:58, eetech00 via groups.io wrote:
I don't recommend the use of tiny valued resistor as jumpers.
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only If something is true: * as far as we know - it's science *for certain - it's mathematics *unquestionably - it's religion

Virus-free.
Re: AC Analysis - show Mag in dBuV versus Freuqncy

 

Hello Ray.Koo,
?
Since you are looking for attenuation characteristic of the filter,? your base reference is immaterial.
Namely it could be dB with respect to any value... say boiled but not peeled potatos .
It is just a ratio value of input versus output or the other way around output versus input with a change in the sign in front of the number.
The is the wisdom of dB or B? or dBu or dBm or dBc or dBa with respect to an appropriate? reference.
In LT spice AC analysis You are instructed to use 1Vac as input. Therefore the output will be specifies in dB with respect to that 1Vac.
?
dbu on the other hand is referenced to 1 uV. As such it specifies voltage ratio not attenuation characteristic ( usual use of dBu and dBm as absolute value references ).
?So enjoy your results in dB and recognise it as the correct value, a ratio of input to output? not a signal level with respect to1 uV or 1 mW into 50 ohm or 1mW into 600 ohm.
Re: Creating a dirt-simple subcircuit component

 

Hi
?
I have two "jumpers" in my library both made from a single zero voltage source.
?
One has a "shorting link" graphic.
One has a "current probe" graphic.
?
I don't recommend the use of tiny valued resistor as jumpers.
Re: Creating a dirt-simple subcircuit component

 

开云体育

That’s what I am using…

?

?

?

From: [email protected] <[email protected]> On Behalf Of BRUCE108
Sent: Sunday, April 13, 2025 2:45 PM
To: [email protected]
Subject: EXTERNAL: Re: [LTspice] Creating a dirt-simple subcircuit component

?

You can use a 0 Volt source as a jumper. This allows differen netnames on each side with 0 vols difference across the source. My distribution has a jumper2 symbol which is not a sub-circuit, but a custom symbol for a 0 Volt source.

?

The contens of the .asy file are:

?

Version 4
SymbolType CELL
LINE Normal 24 64 32 64
LINE Normal -24 64 -32 64
CIRCLE Normal -16 60 -24 68
CIRCLE Normal 16 60 24 68
ARC Normal -20 44 20 84 20 60 -20 60
SYMATTR Prefix V
SYMATTR Value 0
SYMATTR Description A wire jumper that has different node names for each terminal
PIN -32 64 NONE 0
PINATTR PinName +
PINATTR SpiceOrder 1
PIN 32 64 NONE 0
PINATTR PinName -
PINATTR SpiceOrder 2

?

Prefix V with a value 0 is a 0 volt source between two points

?
Re: Creating a dirt-simple subcircuit component

 

You can use a 0 Volt source as a jumper. This allows differen netnames on each side with 0 vols difference across the source. My distribution has a jumper2 symbol which is not a sub-circuit, but a custom symbol for a 0 Volt source.
?
The contens of the .asy file are:
?
Version 4
SymbolType CELL
LINE Normal 24 64 32 64
LINE Normal -24 64 -32 64
CIRCLE Normal -16 60 -24 68
CIRCLE Normal 16 60 24 68
ARC Normal -20 44 20 84 20 60 -20 60
SYMATTR Prefix V
SYMATTR Value 0
SYMATTR Description A wire jumper that has different node names for each terminal
PIN -32 64 NONE 0
PINATTR PinName +
PINATTR SpiceOrder 1
PIN 32 64 NONE 0
PINATTR PinName -
PINATTR SpiceOrder 2
?
Prefix V with a value 0 is a 0 volt source between two points
?
Re: Creating a dirt-simple subcircuit component

 

You can have zero ohm resistor in LTspice, but it doesn't do what you might expect.

If you use one, LTspice just ignores the symbol and the netlist shows that it replaced the resistor with a wire, so both "ends" are the same net.

--
Regards,
Tony?

On Sun, 13 Apr 2025, 20:32 John Waugaman via , <jwaugaman=[email protected]> wrote:
You cannot have a zero-ohm resistor in LTspice.? I've created a jumper with a 1f ohm resistance called MyJmpr.? The simple subcircuit is assigned it to the original jumper symbol and saved as MyJmpr.asy.? I have uploaded it to the Temp files as MyJmpr.zip.? I do like the idea of using a zero-volt voltage source.? You could do the same as I have done with the resistor and assign that as a subcircuit to the original jumper assembly and save the result as a new jumper.
John
?
Re: Creating a dirt-simple subcircuit component

 

开云体育

Yep!

I don’r really like the Jumper symbol, so made it one as a resistor-sized box, marked “0 Ω”

?

From: [email protected] <[email protected]> On Behalf Of John Waugaman via groups.io
Sent: Sunday, April 13, 2025 11:32 AM
To: [email protected]
Subject: EXTERNAL: Re: [LTspice] Creating a dirt-simple subcircuit component

?

You cannot have a zero-ohm resistor in LTspice.? I've created a jumper with a 1f ohm resistance called MyJmpr.? The simple subcircuit is assigned it to the original jumper symbol and saved as MyJmpr.asy.? I have uploaded it to the Temp files as MyJmpr.zip.? I do like the idea of using a zero-volt voltage source.? You could do the same as I have done with the resistor and assign that as a subcircuit to the original jumper assembly and save the result as a new jumper.

John

?
Re: Creating a dirt-simple subcircuit component

 

You cannot have a zero-ohm resistor in LTspice.? I've created a jumper with a 1f ohm resistance called MyJmpr.? The simple subcircuit is assigned it to the original jumper symbol and saved as MyJmpr.asy.? I have uploaded it to the Temp files as MyJmpr.zip.? I do like the idea of using a zero-volt voltage source.? You could do the same as I have done with the resistor and assign that as a subcircuit to the original jumper assembly and save the result as a new jumper.
John
?
Re: Creating a dirt-simple subcircuit component

 

开云体育

SO, no need to include the file name in the symbol Attributes editor?

?

From: [email protected] <[email protected]> On Behalf Of Andy I via groups.io
Sent: Sunday, April 13, 2025 11:22 AM
To: [email protected]
Subject: EXTERNAL: Re: [LTspice] Creating a dirt-simple subcircuit component

?

What "linkage"?

?

The filenames (minus the .ext) must match.? That's all the "linkage" you need.

?

Andy
Re: Creating a dirt-simple subcircuit component

 

No Prefix.
?
Andy
?
Re: Creating a dirt-simple subcircuit component

 

What "linkage"?
?
The filenames (minus the .ext) must match.? That's all the "linkage" you need.
?
Andy
Re: Creating a dirt-simple subcircuit component

 

开云体育

OK:

Erased prefix “X”

Have ZeroOhm OR ZeroOhm.asc in SpiceModel line

All works fine.

?

Thanks!

Dave

?

From: [email protected] <[email protected]> On Behalf Of Andy I via groups.io
Sent: Sunday, April 13, 2025 11:11 AM
To: [email protected]
Subject: EXTERNAL: Re: [LTspice] Creating a dirt-simple subcircuit component

?

Create the symbol from the schematic (.asc) file!

?

Must not have Prefix = X.

?

Andy

?
Re: Creating a dirt-simple subcircuit component

 

开云体育

I did.

Ah!? What prefix, then?

And still, where do I insert the linkage to ZeroOhm.asc?

?

From: [email protected] <[email protected]> On Behalf Of Andy I via groups.io
Sent: Sunday, April 13, 2025 11:11 AM
To: [email protected]
Subject: EXTERNAL: Re: [LTspice] Creating a dirt-simple subcircuit component

?

Create the symbol from the schematic (.asc) file!

?

Must not have Prefix = X.

?

Andy

?
Re: Creating a dirt-simple subcircuit component

 

Create the symbol from the schematic (.asc) file!
?
Must not have Prefix = X.
?
Andy
?
Re: AC Analysis - show Mag in dBuV versus Freuqncy

 

开云体育

If that weird design works for you, OK. This group doesn't do circuit design, but if you want to have a sensible low-pass filter, you could well use one of the filter design apps at

On 2025-04-13 18:52, Ray. Koo via groups.io wrote:
Hi John,
Please see my answer to items 1, 3, and 4.
1. The intention?was twofold, (a) to verify attention rate at -40dB/Dec and (b) to check filter behavior at higher frequencies
2. I could get???into the Vertical?Axis range but ltspice did not display it. That was an interesting suggestion.
3. Caps have esl = 10pH & 20pH, respectively.?
I re-run the simulation with esl and noticed the effect of stray inductances.
4. Yes, you are?correct there.

Very Best,
Ray

On Sun, Apr 13, 2025 at 1:09?AM John Woodgate via <jmw=[email protected]> wrote:

1. If you are only concerned with the response well below 1MHz, there is not much point in sweeping up to 10MHz.

2. You can't change the axis labels to dB?V within LTspice, but you can add text to the plot pane: 0dB = 1?V. With Windows, you can get ? with ALT+0181 on the numerical keypad, with NumLock enabled.

3. To see the effects of even small stray inductances, put 100nH in series with each capacitor. 24 dB gain at about 10 kHz, but see below about input impedance.

4. The input impedance [1V/I(L1)] is very low, less than 1 ohm up to 300 kHz and a minimum of 2 milliohms at about 10 kHz.

On 2025-04-13 02:10, Ray. Koo via wrote:
Hi John,

Thanks for your response.
fc of the first LC is 11.25kHz and that of the second?one is 32.83kHz which are << 1MHz.
I intend to show dBuV?instead of dB on the vertical axis of the Bode plot if that is doable with LTspice.

Thanks,
Ray

On Sat, Apr 12, 2025 at 3:18?PM John Woodgate via <jmw=[email protected]> wrote:

Right-click on V(out) at the top of the plot window and change it to V(out)/1u in the pane that opens. But that is never going to work properly, or as you expect, in practice, because those large capacitors resonate with internal and lead inductances, probably well below 1 MHz.

On 2025-04-12 22:07, Ray. Koo via wrote:
Hi LTspice Group,
?
I have simulated a filter which is a cascaded of two LC low-pass filters.
I get the Bode plot Magnitude in dB versus frequency and phase versus frequency.
?
However, I need to display the magnitude in dBuV versus frequency.
dB is just a value but dBuV is a value with reference 1uV.
I tried few things but no one worked.

Is there a way to show dBuV vs Frequency?
Has anyone tried it before?
?
LCLC filter is uploaded.
?
Comments are appreciated!
Ray
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only If something is true: * as far as we know - it's science *for certain - it's mathematics *unquestionably - it's religion

Virus-free.
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only If something is true: * as far as we know - it's science *for certain - it's mathematics *unquestionably - it's religion
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only If something is true: * as far as we know - it's science *for certain - it's mathematics *unquestionably - it's religion
Re: Creating a dirt-simple subcircuit component

 

开云体育

I understood it to do exactly that, but it merges them in the netlist.

?

From: [email protected] <[email protected]> On Behalf Of Andy I via groups.io
Sent: Sunday, April 13, 2025 10:47 AM
To: [email protected]
Subject: EXTERNAL: Re: [LTspice] Creating a dirt-simple subcircuit component

?

The Jumper symbol is a confusing one, to me at least.? I do not usually see that it actually separates nodenames, but it may allow them.

?

Andy

?
Re: Creating a dirt-simple subcircuit component

 

开云体育

I agree, and have tried but can’t get it right!

I want to link the symbol to ZeroOhm.asc in the same folder.

Where/how to do that? In the symbol editor, Ctrl-A menu, right?

In the Spice Model line?

In the Value line?

With/out the “.asc”?

?

?

From: [email protected] <[email protected]> On Behalf Of Andy I via groups.io
Sent: Sunday, April 13, 2025 10:45 AM
To: [email protected]
Subject: EXTERNAL: Re: [LTspice] Creating a dirt-simple subcircuit component

?

Where is the sUbcircuit?

?

I see a symbol, but not linked to any subcircuit.? That won't work.

?

NSY

?
581 - 600 of 157653