Re: AC Analysis - show Mag in dBuV versus Freuqncy
John Woodgate:
>dBu? is decibels referred to 0.775 V, which is 1 mW in 600 ohms. 0 dBU is not 1mW in 600 ohms.
0 dBU is 0,775 V irrespective of impedance.
0 dBm is 1 mW in 600 ohms.
--------------------
Best regards,
Goran Finnberg
The Mastering Room AB
Goteborg
Sweden
E-mail: mastering@...
Learn from the mistakes of others, you can never live long enough to
make them all yourself.??? -?? John Luther
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Re: Creating a dirt-simple subcircuit component
FYI - not a bad idea to use a custom,?small symbol for a 0 V voltage source, to use either as an ammeter or a net isolator.? Other group members did that already.? Easy to make your own.? Of course it adds the overhead of a custom symbol, which you need to remember to include when sending someone your schematic.
?
Andy
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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
?
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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.
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Re: AC Analysis - show Mag in dBuV versus Freuqncy
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
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Re: Creating a dirt-simple subcircuit component
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
|
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.
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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.
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Re: Creating a dirt-simple subcircuit component
That’s what I am using…
?
?
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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
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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
?
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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?
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
?
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Re: Creating a dirt-simple subcircuit component
Yep!
I don’r really like the Jumper symbol, so made it one as a resistor-sized box, marked “0 Ω”
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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.
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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
?
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Re: Creating a dirt-simple subcircuit component
SO, no need to include the file name in the symbol Attributes editor?
?
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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
?
The filenames (minus the .ext) must match.? That's all the "linkage" you need.
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Re: Creating a dirt-simple subcircuit component
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Re: Creating a dirt-simple subcircuit component
What "linkage"?
?
The filenames (minus the .ext) must match.? That's all the "linkage" you need.
?
Andy
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Re: Creating a dirt-simple subcircuit component
OK:
Erased prefix “X”
Have ZeroOhm OR ZeroOhm.asc in SpiceModel line
All works fine.
?
Thanks!
Dave
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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.
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Re: Creating a dirt-simple subcircuit component
I did.
Ah!? What prefix, then?
And still, where do I insert the linkage to ZeroOhm.asc?
?
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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.
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Re: Creating a dirt-simple subcircuit component
Create the symbol from the schematic (.asc) file!
?
Must not have Prefix = X.
?
Andy
?
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Re: AC Analysis - show Mag in dBuV versus Freuqncy
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
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
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
--
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
|
John Woodgate
Bell, Dave
Tony Casey
John Waugaman