strange LT Spice s/h behavior...

J

John Larkin

Guest
I figured that I could bootstrap an LT Spice sample/hold to make a
stairstep waveform.

Without the RC, the output jumps to +10 volts at the first clock edge.
And the RC has to be right to get a proper stairstep.



Version 4
SHEET 1 880 680
WIRE 144 -128 32 -128
WIRE 240 -128 144 -128
WIRE 448 -128 320 -128
WIRE 144 -80 144 -128
WIRE 448 0 448 -128
WIRE 144 16 144 -16
WIRE 32 96 32 -128
WIRE 192 96 32 96
WIRE 192 128 32 128
WIRE 448 144 448 80
WIRE 448 144 368 144
WIRE 576 144 448 144
WIRE 32 160 32 128
WIRE 192 160 96 160
WIRE 96 208 96 160
WIRE 96 320 96 288
FLAG 96 320 0
FLAG 32 160 0
FLAG 144 16 0
SYMBOL SpecialFunctions\\\\sample 272 128 R0
WINDOW 0 -16 -113 Left 2
WINDOW 3 -56 -83 Left 2
SYMATTR InstName A1
SYMATTR Value ROUT=1m
SYMBOL voltage 96 192 R0
WINDOW 0 48 76 Left 2
WINDOW 3 21 110 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value PULSE(0 1 10u 1n 1n 500n 1u 1e6)
SYMBOL voltage 448 -16 R0
WINDOW 0 57 42 Left 2
WINDOW 3 49 76 Left 2
SYMATTR InstName V2
SYMATTR Value 500m
SYMBOL res 336 -144 R90
WINDOW 0 77 55 VBottom 2
WINDOW 3 85 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 1k
SYMBOL cap 128 -80 R0
WINDOW 0 -56 19 Left 2
WINDOW 3 -59 49 Left 2
SYMATTR InstName C1
SYMATTR Value 10p
TEXT -200 112 Left 2 !.tran 100u
TEXT -216 8 Left 2 ;S/H Stairstep
TEXT -224 56 Left 2 ;JL Aug 12 2022


--

John Larkin Highland Technology, Inc trk

The cork popped merrily, and Lord Peter rose to his feet.
\"Bunter\", he said, \"I give you a toast. The triumph of Instinct over Reason\"
 
John Larkin wrote:
I figured that I could bootstrap an LT Spice sample/hold to make a
stairstep waveform.

Without the RC, the output jumps to +10 volts at the first clock edge.
And the RC has to be right to get a proper stairstep.
Click to expand...

Didn\'t try it out, but did you use the vanilla trap solver or the tricky
one?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
On Fri, 12 Aug 2022 16:05:46 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
I figured that I could bootstrap an LT Spice sample/hold to make a
stairstep waveform.

Without the RC, the output jumps to +10 volts at the first clock edge.
And the RC has to be right to get a proper stairstep.


Didn\'t try it out, but did you use the vanilla trap solver or the tricky
one?

Cheers

Phil Hobbs
Click to expand...

Mod trap, alternate. I\'ll try something else.
 
On Fri, 12 Aug 2022 13:16:07 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

On Fri, 12 Aug 2022 16:05:46 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
I figured that I could bootstrap an LT Spice sample/hold to make a
stairstep waveform.

Without the RC, the output jumps to +10 volts at the first clock edge.
And the RC has to be right to get a proper stairstep.


Didn\'t try it out, but did you use the vanilla trap solver or the tricky
one?

Cheers

Phil Hobbs

Mod trap, alternate. I\'ll try something else.
Click to expand...

Control panel, spice, reset to default (mod trap, normal solver) it
behaves the same.
 
On Fri, 12 Aug 2022 12:47:59 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

I figured that I could bootstrap an LT Spice sample/hold to make a
stairstep waveform.

Without the RC, the output jumps to +10 volts at the first clock edge.
And the RC has to be right to get a proper stairstep.
Click to expand...

So it works with the RC - suggests a linear condition is
permitted at the sampling time. Perhaps the internal
gates aren\'t timed to prevent signal shoot-through.

RL
 
On Fri, 12 Aug 2022 20:28:14 -0400, legg <legg@nospam.magma.ca> wrote:

On Fri, 12 Aug 2022 12:47:59 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:

I figured that I could bootstrap an LT Spice sample/hold to make a
stairstep waveform.

Without the RC, the output jumps to +10 volts at the first clock edge.
And the RC has to be right to get a proper stairstep.


So it works with the RC - suggests a linear condition is
permitted at the sampling time. Perhaps the internal
gates aren\'t timed to prevent signal shoot-through.

RL
Click to expand...

I can\'t understand it. Even 1K and 1 fF allows it to make a staircase.
But 1K and 0 fF doesn\'t.

Obviously something is goofy inside the s/h model, but I wouldn\'t know
how to accomplish that.

I can do what I want to do, by adding an RC, but I don\'t understand
it.
 
On Fri, 12 Aug 2022 12:47:59 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

I figured that I could bootstrap an LT Spice sample/hold to make a
stairstep waveform.

Without the RC, the output jumps to +10 volts at the first clock edge.
And the RC has to be right to get a proper stairstep.



Version 4
SHEET 1 880 680
WIRE 144 -128 32 -128
WIRE 240 -128 144 -128
WIRE 448 -128 320 -128
WIRE 144 -80 144 -128
WIRE 448 0 448 -128
WIRE 144 16 144 -16
WIRE 32 96 32 -128
WIRE 192 96 32 96
WIRE 192 128 32 128
WIRE 448 144 448 80
WIRE 448 144 368 144
WIRE 576 144 448 144
WIRE 32 160 32 128
WIRE 192 160 96 160
WIRE 96 208 96 160
WIRE 96 320 96 288
FLAG 96 320 0
FLAG 32 160 0
FLAG 144 16 0
SYMBOL SpecialFunctions\\\\sample 272 128 R0
WINDOW 0 -16 -113 Left 2
WINDOW 3 -56 -83 Left 2
SYMATTR InstName A1
SYMATTR Value ROUT=1m
SYMBOL voltage 96 192 R0
WINDOW 0 48 76 Left 2
WINDOW 3 21 110 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value PULSE(0 1 10u 1n 1n 500n 1u 1e6)
SYMBOL voltage 448 -16 R0
WINDOW 0 57 42 Left 2
WINDOW 3 49 76 Left 2
SYMATTR InstName V2
SYMATTR Value 500m
SYMBOL res 336 -144 R90
WINDOW 0 77 55 VBottom 2
WINDOW 3 85 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 1k
SYMBOL cap 128 -80 R0
WINDOW 0 -56 19 Left 2
WINDOW 3 -59 49 Left 2
SYMATTR InstName C1
SYMATTR Value 10p
TEXT -200 112 Left 2 !.tran 100u
TEXT -216 8 Left 2 ;S/H Stairstep
TEXT -224 56 Left 2 ;JL Aug 12 2022
Click to expand...

Even the RC is dicey. The best thing is to add a delay line at the s/h
input.
 
On Fri, 12 Aug 2022 18:41:32 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

On Fri, 12 Aug 2022 20:28:14 -0400, legg <legg@nospam.magma.ca> wrote:

On Fri, 12 Aug 2022 12:47:59 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:

I figured that I could bootstrap an LT Spice sample/hold to make a
stairstep waveform.

Without the RC, the output jumps to +10 volts at the first clock edge.
And the RC has to be right to get a proper stairstep.


So it works with the RC - suggests a linear condition is
permitted at the sampling time. Perhaps the internal
gates aren\'t timed to prevent signal shoot-through.

RL

I can\'t understand it. Even 1K and 1 fF allows it to make a staircase.
But 1K and 0 fF doesn\'t.

Obviously something is goofy inside the s/h model, but I wouldn\'t know
how to accomplish that.

I can do what I want to do, by adding an RC, but I don\'t understand
it.
Click to expand...

Stick 50R in series with the SH inputs and look at the voltages on
each side of the resistor. This shouldn\'t normally \'break\' a S/H,
should it?

RL
 
On Fri, 12 Aug 2022 18:41:32 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

On Fri, 12 Aug 2022 20:28:14 -0400, legg <legg@nospam.magma.ca> wrote:

On Fri, 12 Aug 2022 12:47:59 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:

I figured that I could bootstrap an LT Spice sample/hold to make a
stairstep waveform.

Without the RC, the output jumps to +10 volts at the first clock edge.
And the RC has to be right to get a proper stairstep.


So it works with the RC - suggests a linear condition is
permitted at the sampling time. Perhaps the internal
gates aren\'t timed to prevent signal shoot-through.

RL

I can\'t understand it. Even 1K and 1 fF allows it to make a staircase.
But 1K and 0 fF doesn\'t.

Obviously something is goofy inside the s/h model, but I wouldn\'t know
how to accomplish that.

I can do what I want to do, by adding an RC, but I don\'t understand
it.
Click to expand...

The S/H input has no current flow.

Perhaps the modeler forgot a default zin.

RL
 
On Fri, 12 Aug 2022 18:41:32 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

On Fri, 12 Aug 2022 20:28:14 -0400, legg <legg@nospam.magma.ca> wrote:

On Fri, 12 Aug 2022 12:47:59 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:

I figured that I could bootstrap an LT Spice sample/hold to make a
stairstep waveform.

Without the RC, the output jumps to +10 volts at the first clock edge.
And the RC has to be right to get a proper stairstep.


So it works with the RC - suggests a linear condition is
permitted at the sampling time. Perhaps the internal
gates aren\'t timed to prevent signal shoot-through.

RL

I can\'t understand it. Even 1K and 1 fF allows it to make a staircase.
But 1K and 0 fF doesn\'t.

Obviously something is goofy inside the s/h model, but I wouldn\'t know
how to accomplish that.

I can do what I want to do, by adding an RC, but I don\'t understand
it.
Click to expand...

In a sim where the staircase ends prematurely (C1<=1f), C1 has no
current during the final, out-sized signal rise, though it shows
well defined values in previous \'normal\' steps.

RL
 
On Fri, 12 Aug 2022 21:19:06 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

On Fri, 12 Aug 2022 12:47:59 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:

I figured that I could bootstrap an LT Spice sample/hold to make a
stairstep waveform.

Without the RC, the output jumps to +10 volts at the first clock edge.
And the RC has to be right to get a proper stairstep.

snip
TEXT -216 8 Left 2 ;S/H Stairstep
TEXT -224 56 Left 2 ;JL Aug 12 2022

Even the RC is dicey. The best thing is to add a delay line at the s/h
input.
Click to expand...

LTspice group on io says the sample is instantaneous without internal
delays - that direct gain is possible. Uncommented defaulkt output Z
is iK. A Td statement will have no effect.

Says not to worry - you can\'t buy one of these anyways.

RL
 
On Mon, 15 Aug 2022 11:17:03 -0400, legg <legg@nospam.magma.ca> wrote:

On Fri, 12 Aug 2022 21:19:06 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:

On Fri, 12 Aug 2022 12:47:59 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:

I figured that I could bootstrap an LT Spice sample/hold to make a
stairstep waveform.

Without the RC, the output jumps to +10 volts at the first clock edge.
And the RC has to be right to get a proper stairstep.

snip
TEXT -216 8 Left 2 ;S/H Stairstep
TEXT -224 56 Left 2 ;JL Aug 12 2022

Even the RC is dicey. The best thing is to add a delay line at the s/h
input.

LTspice group on io says the sample is instantaneous without internal
delays - that direct gain is possible. Uncommented defaulkt output Z
is iK. A Td statement will have no effect.
Click to expand...

It\'s still very weird.

Says not to worry - you can\'t buy one of these anyways.

RL
Click to expand...

A few people used to make analog s/h chips, but I think they are gone.
 
On Mon, 15 Aug 2022 09:14:48 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Mon, 15 Aug 2022 11:17:03 -0400, legg <legg@nospam.magma.ca> wrote:

On Fri, 12 Aug 2022 21:19:06 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:

On Fri, 12 Aug 2022 12:47:59 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:

I figured that I could bootstrap an LT Spice sample/hold to make a
stairstep waveform.

Without the RC, the output jumps to +10 volts at the first clock edge.
And the RC has to be right to get a proper stairstep.

snip
TEXT -216 8 Left 2 ;S/H Stairstep
TEXT -224 56 Left 2 ;JL Aug 12 2022

Even the RC is dicey. The best thing is to add a delay line at the s/h
input.

LTspice group on io says the sample is instantaneous without internal
delays - that direct gain is possible. Uncommented defaulkt output Z
is iK. A Td statement will have no effect.

It\'s still very weird.


Says not to worry - you can\'t buy one of these anyways.

RL

A few people used to make analog s/h chips, but I think they are gone.
Click to expand...

Actually, there are some.

https://www.mouser.com/c/semiconductors/amplifier-ics/sample-hold-amplifiers/?gclid=EAIaIQobChMI4anyg-zJ-QIVWRatBh0xXQHuEAAYAiAAEgLP4vD_BwE
 
On Mon, 15 Aug 2022 15:01:03 -0700, John Larkin
<jlarkin@highland_atwork_technology.com> wrote:

On Mon, 15 Aug 2022 09:14:48 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Mon, 15 Aug 2022 11:17:03 -0400, legg <legg@nospam.magma.ca> wrote:

On Fri, 12 Aug 2022 21:19:06 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:

On Fri, 12 Aug 2022 12:47:59 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:

I figured that I could bootstrap an LT Spice sample/hold to make a
stairstep waveform.

Without the RC, the output jumps to +10 volts at the first clock edge.
And the RC has to be right to get a proper stairstep.

snip
TEXT -216 8 Left 2 ;S/H Stairstep
TEXT -224 56 Left 2 ;JL Aug 12 2022

Even the RC is dicey. The best thing is to add a delay line at the s/h
input.

LTspice group on io says the sample is instantaneous without internal
delays - that direct gain is possible. Uncommented defaulkt output Z
is iK. A Td statement will have no effect.

It\'s still very weird.


Says not to worry - you can\'t buy one of these anyways.

RL

A few people used to make analog s/h chips, but I think they are gone.

Actually, there are some.

https://www.mouser.com/c/semiconductors/amplifier-ics/sample-hold-amplifiers/?gclid=EAIaIQobChMI4anyg-zJ-QIVWRatBh0xXQHuEAAYAiAAEgLP4vD_BwE
Click to expand...

The \'sample\' subcircuit is not a model of any of these
parts, hence the purchasing non-information.

RL
 
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