# Can't Change Vss in LTSpice, Need Help

#### Yunus Emre SERT

Joined Jul 11, 2019
13
Hello,

I am trying to get +3V/-3V square signal from Q5 of CD4024B but since I'm not able to change Vss value of the IC, I get +3V / 0V signal instead of +3V/-3V signal. Can you show me a way to arrange it?

Additional Info: In fact, my main purpose is getting the signal from Q4 of CD4060B but my lib includes CD4060Bg and it both doesn't work and has the same problem also.

The files are attached. As you can see, if there were any pin for VDD and VSS, I would label them and use the voltage sources on the left side. Because no pins exist, I tried to edit properties but only VDD was shown. I can change it by editing or parametrizing but I need to change VSS. Need your help.

Thanks, regards...

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#### ci139

Joined Jul 11, 2016
1,696
Param Default Description
Vlow 0 Logic low level
see : http://ltwiki.org/index.php?title=A_Special_functions
. . . but you may need to modify the CD4000 (if it does not enable remote def. by .param internal in .lib)
in 4024 def you need to provide all subcircuits with the support (if there isn't)
Code:
* the definition of the subcircuit
.SUBCKT MyChip 1 2 3 4 PARAMS: R1=1k R2=2k
.param VarR1={R1} VarR2={R2}
r1 1 2 R = VarR1
r2 3 4 R = VarR2
.ENDS
but it's quite a lot of work ... as you need to (copy+rename the .lib) and add Vhigh={VhiFixed} Vlo={LoFixed} to all A - circuit elements and maybe more in CD4000_v.lib

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#### eetech00

Joined Jun 8, 2013
2,482
Hello,

I am trying to get +3V/-3V square signal from Q5 of CD4024B but since I'm not able to change Vss value of the IC, I get +3V / 0V signal instead of +3V/-3V signal. Can you show me a way to arrange it?

Additional Info: In fact, my main purpose is getting the signal from Q4 of CD4060B but my lib includes CD4060Bg and it both doesn't work and has the same problem also.

The files are attached. As you can see, if there were any pin for VDD and VSS, I would label them and use the voltage sources on the left side. Because no pins exist, I tried to edit properties but only VDD was shown. I can change it by editing or parametrizing but I need to change VSS. Need your help.

Thanks, regards...
Hi

Change "Spicemodel" attribute in symbol.

Also, you need to use the CD4000_v.lib library that supports external supply pins.

eT

#### Yunus Emre SERT

Joined Jul 11, 2019
13
Hi

Change "Spicemodel" attribute in symbol.

Also, you need to use the CD4000_v.lib library that supports external supply pins.

eT

View attachment 185920

#### ci139

Joined Jul 11, 2016
1,696
as infact you do not need to modify anything but your label names/voltages
Vdd_6V → Vdd_3V (←Voltage value here is still 6V)
Undefined → V_Ref (←Voltage value here is set to 3V)
GND , 0V → GND (←Voltage value here is still 0V)

but if you operate your circuit you reference your signal against +3v V_Ref . . . so Output V(OUT,V_Ref) results in ±3V

((tough it gonna be a bit messy to get acustomized with if the circuit goes more complex ))

#### Yunus Emre SERT

Joined Jul 11, 2019
13
as infact you do not need to modify anything but your label names/voltages
Vdd_6V → Vdd_3V (←Voltage value here is still 6V)
Undefined → V_Ref (←Voltage value here is set to 3V)
GND , 0V → GND (←Voltage value here is still 0V)

but if you operate your circuit you reference your signal against +3v V_Ref . . . so Output V(OUT,V_Ref) results in ±3V

((tough it gonna be a bit messy to get acustomized with if the circuit goes more complex ))
I am more confused now Actually I'm not used to LTspice, so I don't know how to do arrangements that you told.

#### eetech00

Joined Jun 8, 2013
2,482
I am more confused now Actually I'm not used to LTspice, so I don't know how to do arrangements that you told.
Follow the way I showed in post #3.

eT

#### crutschow

Joined Mar 14, 2008
27,394
All the circuit CMOS logic levels will then be ±3V.
Is that okay?

If you only need one signal to be ±3V, then it might be easier just to use a level shifter on that signal.
Below is the LTspice simulation of an example 2-transistor, 3-resistor circuit to do that.

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#### eetech00

Joined Jun 8, 2013
2,482
Hi

All I did was make changes as described in post #3.

eT