Hicom%252Flit%252Fgpn%252Flmc6482
I have a voltage, only present for halfsine peak of 2MHz (500ns wide), which is 500V peak.
I need to know the peak voltage, in an embedded system where the ADC samples at max 5MSa. So way too slow to find the peak.
Figure 7-23 of this datasheet has a classic peak detector:
https://www.ti.com/lit/ds/symlink/lmc6482.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&ts=1703760014317&ref_url=https%253A%252F%252Fwww.ti.com%252Fgeneral%252Fdocs%252Fsuppproductinfo.tsp%253FdistId%253D10%2526gotoUrl%253Dhttps%253A%252F%252Fwww.ti.
But for a 2MHz signal, I would need a very fast opamp.complicated.
I have done simple peak detection, with a diode, and a sample capacitor, followed with an opamp, but nothing is really good.
In this case I have 95k/5k resistor to bring the voltage down to 24V, since then the simple diode drop won't matter much. But 30V opamps are slooooow, so no real good option.
I tried using an emitter follower, but it has a funny peak where the base voltage is higher than the peak voltage, and also has potential to die due to Veb voltage.
One idea I had, use the 24V divider with the diode, then right after the pulse, activate another resistive divider with an FET to bring it to 5V where fast opamps are cheaper. The FET will only turn on as long as to sample the voltage, but seems overly
Any favorite peak detector?
Hicom%252Flit%252Fgpn%252Flmc6482
I have a voltage, only present for halfsine peak of 2MHz (500ns wide), which is 500V peak.
I need to know the peak voltage, in an embedded system where the ADC samples at max 5MSa. So way too slow to find the peak.
Figure 7-23 of this datasheet has a classic peak detector:
https://www.ti.com/lit/ds/symlink/lmc6482.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&ts=1703760014317&ref_url=https%253A%252F%252Fwww.ti.com%252Fgeneral%252Fdocs%252Fsuppproductinfo.tsp%253FdistId%253D10%2526gotoUrl%253Dhttps%253A%252F%252Fwww.ti.
But for a 2MHz signal, I would need a very fast opamp.complicated.
I have done simple peak detection, with a diode, and a sample capacitor, followed with an opamp, but nothing is really good.
In this case I have 95k/5k resistor to bring the voltage down to 24V, since then the simple diode drop won't matter much. But 30V opamps are slooooow, so no real good option.
I tried using an emitter follower, but it has a funny peak where the base voltage is higher than the peak voltage, and also has potential to die due to Veb voltage.
One idea I had, use the 24V divider with the diode, then right after the pulse, activate another resistive divider with an FET to bring it to 5V where fast opamps are cheaper. The FET will only turn on as long as to sample the voltage, but seems overly
Any favorite peak detector?
Hicom%252Flit%252Fgpn%252Flmc6482
I have a voltage, only present for halfsine peak of 2MHz (500ns wide), which is 500V peak.
I need to know the peak voltage, in an embedded system where the ADC
samples at max 5MSa. So way too slow to find the peak.
Figure 7-23 of this datasheet has a classic peak detector:
https://www.ti.com/lit/ds/symlink/lmc6482.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&ts03760014317&ref_url=https%253A%252F%252Fwww.ti.com%252Fgeneral%252Fdocs%252Fsuppproductinfo.tsp%253FdistId%253D10%2526gotoUrl%253Dhttps%253A%252F%252Fwww.ti.
But for a 2MHz signal, I would need a very fast opamp.
I have done simple peak detection, with a diode, and a sample capacitor, followed with an opamp, but nothing is really good.
In this case I have 95k/5k resistor to bring the voltage down to 24V,
since then the simple diode drop won't matter much. But 30V opamps are slooooow, so no real good option.
I tried using an emitter follower, but it has a funny peak where the base voltage is higher than the peak voltage, and also has potential to die due to Veb voltage.
One idea I had, use the 24V divider with the diode, then right after the pulse, activate another resistive divider with an FET to bring it to 5V
where fast opamps are cheaper. The FET will only turn on as long as to
sample the voltage, but seems overly complicated.
Any favorite peak detector?
fredag den 29. december 2023 kl. 02.11.07 UTC+1 skrev Klaus Kragelund:com%252Flit%252Fgpn%252Flmc6482
Hi
I have a voltage, only present for halfsine peak of 2MHz (500ns wide), which is 500V peak.
I need to know the peak voltage, in an embedded system where the ADC samples at max 5MSa. So way too slow to find the peak.
Figure 7-23 of this datasheet has a classic peak detector:
https://www.ti.com/lit/ds/symlink/lmc6482.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&ts=1703760014317&ref_url=https%253A%252F%252Fwww.ti.com%252Fgeneral%252Fdocs%252Fsuppproductinfo.tsp%253FdistId%253D10%2526gotoUrl%253Dhttps%253A%252F%252Fwww.ti.
overly complicated.
But for a 2MHz signal, I would need a very fast opamp.
I have done simple peak detection, with a diode, and a sample capacitor, followed with an opamp, but nothing is really good.
In this case I have 95k/5k resistor to bring the voltage down to 24V, since then the simple diode drop won't matter much. But 30V opamps are slooooow, so no real good option.
I tried using an emitter follower, but it has a funny peak where the base voltage is higher than the peak voltage, and also has potential to die due to Veb voltage.
One idea I had, use the 24V divider with the diode, then right after the pulse, activate another resistive divider with an FET to bring it to 5V where fast opamps are cheaper. The FET will only turn on as long as to sample the voltage, but seems
Any favorite peak detector?
https://www.analog.com/en/design-notes/peak-detectors-gain-in-speed-performance.html ?
On Thursday, December 28, 2023 at 5:11:07?PM UTC-8, Klaus Kragelund wrote:com%252Flit%252Fgpn%252Flmc6482
Hi
I have a voltage, only present for halfsine peak of 2MHz (500ns wide), which is 500V peak.
I need to know the peak voltage, in an embedded system where the ADC samples at max 5MSa. So way too slow to find the peak.
Figure 7-23 of this datasheet has a classic peak detector:
https://www.ti.com/lit/ds/symlink/lmc6482.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&ts=1703760014317&ref_url=https%253A%252F%252Fwww.ti.com%252Fgeneral%252Fdocs%252Fsuppproductinfo.tsp%253FdistId%253D10%2526gotoUrl%253Dhttps%253A%252F%252Fwww.ti.
But for a 2MHz signal, I would need a very fast opamp.
That's a variant on the Wilkinson D/A converter's peak detector; charge a capacitor in the op-amp-as-follower
way, through a diode, and when peak occurs, suddenly the op amp tries to reverse the current
through that diode (and dives fast, making a nice edge).
It doesn't need to be an op amp follower, a simple fast transistor can fit that role too.
Especially since you have 500V to play with; it'd be normal to use a capacitive divider
and maybe just a MOSFET without much gate sensitivity.
Reset after the peak is gonna take some current sink to discharge the capacitor, and a bit of dead time
before you reenergize the input.
On 29/12/2023 01:25, Lasse Langwadt Christensen wrote:ti.com%252Flit%252Fgpn%252Flmc6482
fredag den 29. december 2023 kl. 02.11.07 UTC+1 skrev Klaus Kragelund:
Hi
I have a voltage, only present for halfsine peak of 2MHz (500ns wide), which is 500V peak.
I need to know the peak voltage, in an embedded system where the ADC samples at max 5MSa. So way too slow to find the peak.
Figure 7-23 of this datasheet has a classic peak detector:
https://www.ti.com/lit/ds/symlink/lmc6482.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&ts=1703760014317&ref_url=https%253A%252F%252Fwww.ti.com%252Fgeneral%252Fdocs%252Fsuppproductinfo.tsp%253FdistId%253D10%2526gotoUrl%253Dhttps%253A%252F%252Fwww.
overly complicated.
But for a 2MHz signal, I would need a very fast opamp.
I have done simple peak detection, with a diode, and a sample capacitor, followed with an opamp, but nothing is really good.
In this case I have 95k/5k resistor to bring the voltage down to 24V, since then the simple diode drop won't matter much. But 30V opamps are slooooow, so no real good option.
I tried using an emitter follower, but it has a funny peak where the base voltage is higher than the peak voltage, and also has potential to die due to Veb voltage.
One idea I had, use the 24V divider with the diode, then right after the pulse, activate another resistive divider with an FET to bring it to 5V where fast opamps are cheaper. The FET will only turn on as long as to sample the voltage, but seems
Any favorite peak detector?
https://www.analog.com/en/design-notes/peak-detectors-gain-in-speed-performance.html ?
Instead of op-amp use a comparator, they are often much faster?
piglet
On Fri, 29 Dec 2023 08:11:43 +0000, piglet <erichpwagner@hotmail.com>ti.com%252Flit%252Fgpn%252Flmc6482
wrote:
On 29/12/2023 01:25, Lasse Langwadt Christensen wrote:
fredag den 29. december 2023 kl. 02.11.07 UTC+1 skrev Klaus Kragelund:
Hi
I have a voltage, only present for halfsine peak of 2MHz (500ns wide), which is 500V peak.
I need to know the peak voltage, in an embedded system where the ADC samples at max 5MSa. So way too slow to find the peak.
Figure 7-23 of this datasheet has a classic peak detector:
https://www.ti.com/lit/ds/symlink/lmc6482.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&ts=1703760014317&ref_url=https%253A%252F%252Fwww.ti.com%252Fgeneral%252Fdocs%252Fsuppproductinfo.tsp%253FdistId%253D10%2526gotoUrl%253Dhttps%253A%252F%252Fwww.
overly complicated.
But for a 2MHz signal, I would need a very fast opamp.
I have done simple peak detection, with a diode, and a sample capacitor, followed with an opamp, but nothing is really good.
In this case I have 95k/5k resistor to bring the voltage down to 24V, since then the simple diode drop won't matter much. But 30V opamps are slooooow, so no real good option.
I tried using an emitter follower, but it has a funny peak where the base voltage is higher than the peak voltage, and also has potential to die due to Veb voltage.
One idea I had, use the 24V divider with the diode, then right after the pulse, activate another resistive divider with an FET to bring it to 5V where fast opamps are cheaper. The FET will only turn on as long as to sample the voltage, but seems
Any favorite peak detector?
https://www.analog.com/en/design-notes/peak-detectors-gain-in-speed-performance.html ?
Instead of op-amp use a comparator, they are often much faster?
piglet
One could divide down and use a comparator. Basicaslly slowly tease
the other input of the comparator until it's tripping about half the
time.
If his ADC sample time is fast, he could random or equivalent-time
sample to find the peak. Just make the ADC clock async to the HV
pulse.
Here's the monitor pickoff from my Pockels Cell driver. The pulse is
about 1400v 7ns, sort of half-sine. Could have used a BUF602.
https://www.dropbox.com/scl/fi/8s5xexx4n9i1eyhgxtps8/T850_Pickoff.jpg?rlkey=bsq2uemyy9ijdruiq6lqnwdw0&raw=1
https://www.dropbox.com/scl/fi/rfoqchosbazddbql8smut/DSC02778.JPG?rlkey=wm0k2ys2917n8krscptwvss9p&raw=1
On Thursday, December 28, 2023 at 8:11:07?PM UTC-5, Klaus Kragelund wrote:com%252Flit%252Fgpn%252Flmc6482
Hi
I have a voltage, only present for halfsine peak of 2MHz (500ns wide), which is 500V peak.
I need to know the peak voltage, in an embedded system where the ADC samples at max 5MSa. So way too slow to find the peak.
Figure 7-23 of this datasheet has a classic peak detector:
https://www.ti.com/lit/ds/symlink/lmc6482.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&ts=1703760014317&ref_url=https%253A%252F%252Fwww.ti.com%252Fgeneral%252Fdocs%252Fsuppproductinfo.tsp%253FdistId%253D10%2526gotoUrl%253Dhttps%253A%252F%252Fwww.ti.
overly complicated.
But for a 2MHz signal, I would need a very fast opamp.
I have done simple peak detection, with a diode, and a sample capacitor, followed with an opamp, but nothing is really good.
In this case I have 95k/5k resistor to bring the voltage down to 24V, since then the simple diode drop won't matter much. But 30V opamps are slooooow, so no real good option.
I tried using an emitter follower, but it has a funny peak where the base voltage is higher than the peak voltage, and also has potential to die due to Veb voltage.
One idea I had, use the 24V divider with the diode, then right after the pulse, activate another resistive divider with an FET to bring it to 5V where fast opamps are cheaper. The FET will only turn on as long as to sample the voltage, but seems
like the sampling comparator works well many times.
Any favorite peak detector?
Does the peak measurement have to be single-shot or it can it take several cycles? If you want single-shot, it's going to be pricey. Something like the OPA615 will do it. If you can work with an integrated measurement, it will be 1/3 the cost, something
On 29/12/2023 16:27, John Larkin wrote:ti.com%252Flit%252Fgpn%252Flmc6482
On Fri, 29 Dec 2023 08:11:43 +0000, piglet <erichpwagner@hotmail.com>
wrote:
On 29/12/2023 01:25, Lasse Langwadt Christensen wrote:
fredag den 29. december 2023 kl. 02.11.07 UTC+1 skrev Klaus Kragelund: >>>>> Hi
I have a voltage, only present for halfsine peak of 2MHz (500ns wide), which is 500V peak.
I need to know the peak voltage, in an embedded system where the ADC samples at max 5MSa. So way too slow to find the peak.
Figure 7-23 of this datasheet has a classic peak detector:
https://www.ti.com/lit/ds/symlink/lmc6482.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&ts=1703760014317&ref_url=https%253A%252F%252Fwww.ti.com%252Fgeneral%252Fdocs%252Fsuppproductinfo.tsp%253FdistId%253D10%2526gotoUrl%253Dhttps%253A%252F%252Fwww.
overly complicated.
But for a 2MHz signal, I would need a very fast opamp.
I have done simple peak detection, with a diode, and a sample capacitor, followed with an opamp, but nothing is really good.
In this case I have 95k/5k resistor to bring the voltage down to 24V, since then the simple diode drop won't matter much. But 30V opamps are slooooow, so no real good option.
I tried using an emitter follower, but it has a funny peak where the base voltage is higher than the peak voltage, and also has potential to die due to Veb voltage.
One idea I had, use the 24V divider with the diode, then right after the pulse, activate another resistive divider with an FET to bring it to 5V where fast opamps are cheaper. The FET will only turn on as long as to sample the voltage, but seems
Any favorite peak detector?
https://www.analog.com/en/design-notes/peak-detectors-gain-in-speed-performance.html ?
Instead of op-amp use a comparator, they are often much faster?
piglet
One could divide down and use a comparator. Basicaslly slowly tease
the other input of the comparator until it's tripping about half the
time.
If his ADC sample time is fast, he could random or equivalent-time
sample to find the peak. Just make the ADC clock async to the HV
pulse.
Here's the monitor pickoff from my Pockels Cell driver. The pulse is
about 1400v 7ns, sort of half-sine. Could have used a BUF602.
https://www.dropbox.com/scl/fi/8s5xexx4n9i1eyhgxtps8/T850_Pickoff.jpg?rlkey=bsq2uemyy9ijdruiq6lqnwdw0&raw=1
https://www.dropbox.com/scl/fi/rfoqchosbazddbql8smut/DSC02778.JPG?rlkey=wm0k2ys2917n8krscptwvss9p&raw=1
I meant just use comp in place of op-amp in the classic peak hold
circuit. For negative going peaks an open drain comparator makes for
very low parts count :)
Here is what I meant, it gets progressively more accurate at slower dv/dt:
Version 4
SHEET 1 880 680
WIRE 16 -32 -416 -32
WIRE -512 32 -512 0
WIRE 16 32 16 -32
WIRE 480 48 64 48
WIRE 128 128 128 96
WIRE 64 144 64 48
WIRE 96 144 64 144
WIRE -512 160 -512 112
WIRE 256 160 160 160
WIRE 384 160 320 160
WIRE 480 160 480 48
WIRE 480 160 384 160
WIRE -416 176 -416 -32
WIRE 16 176 16 112
WIRE 96 176 16 176
WIRE 480 192 480 160
WIRE 16 208 16 176
WIRE 384 208 384 160
WIRE -416 320 -416 256
WIRE 16 320 16 288
WIRE 128 320 128 192
WIRE 384 320 384 272
WIRE 480 320 480 272
FLAG -416 320 0
FLAG -512 160 0
FLAG 128 320 0
FLAG 16 320 0
FLAG 384 320 0
FLAG 480 320 0
FLAG 128 96 P5
FLAG -512 0 P5
FLAG 480 48 OUT
SYMBOL Comparators\\LT1720 128 96 R0
SYMATTR InstName U1
SYMBOL cap 368 208 R0
SYMATTR InstName C1
SYMATTR Value 470p
SYMBOL voltage -512 16 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 5
SYMBOL voltage -416 160 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value SINE(0 500 2meg 0 0 0 0.5)
SYMBOL res 32 128 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R1
SYMATTR Value 199k
SYMBOL res 32 304 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 1k
SYMBOL res 464 176 R0
SYMATTR InstName R3
SYMATTR Value 100k
SYMBOL diode 256 176 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D1
SYMATTR Value 1N4148
TEXT -562 344 Left 2 !.tran 2u
TEXT 376 -144 Left 2 ;EPW SED
TEXT 368 -104 Left 2 ;DEC 2023
TEXT -152 -144 Left 2 ;SHOWING COMPARATOR AS PEAK DET
piglet
On Fri, 29 Dec 2023 19:49:01 +0000, piglet <erichpwagner@hotmail.com>252Fwww.ti.com%252Flit%252Fgpn%252Flmc6482
wrote:
On 29/12/2023 16:27, John Larkin wrote:
On Fri, 29 Dec 2023 08:11:43 +0000, piglet <erichpwagner@hotmail.com>
wrote:
On 29/12/2023 01:25, Lasse Langwadt Christensen wrote:
fredag den 29. december 2023 kl. 02.11.07 UTC+1 skrev Klaus Kragelund: >>>>>> Hi
I have a voltage, only present for halfsine peak of 2MHz (500ns wide), which is 500V peak.
I need to know the peak voltage, in an embedded system where the ADC samples at max 5MSa. So way too slow to find the peak.
Figure 7-23 of this datasheet has a classic peak detector:
https://www.ti.com/lit/ds/symlink/lmc6482.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&ts=1703760014317&ref_url=https%253A%252F%252Fwww.ti.com%252Fgeneral%252Fdocs%252Fsuppproductinfo.tsp%253FdistId%253D10%2526gotoUrl%253Dhttps%253A%252F%
overly complicated.
But for a 2MHz signal, I would need a very fast opamp.
I have done simple peak detection, with a diode, and a sample capacitor, followed with an opamp, but nothing is really good.
In this case I have 95k/5k resistor to bring the voltage down to 24V, since then the simple diode drop won't matter much. But 30V opamps are slooooow, so no real good option.
I tried using an emitter follower, but it has a funny peak where the base voltage is higher than the peak voltage, and also has potential to die due to Veb voltage.
One idea I had, use the 24V divider with the diode, then right after the pulse, activate another resistive divider with an FET to bring it to 5V where fast opamps are cheaper. The FET will only turn on as long as to sample the voltage, but seems
Any favorite peak detector?
https://www.analog.com/en/design-notes/peak-detectors-gain-in-speed-performance.html ?
Instead of op-amp use a comparator, they are often much faster?
piglet
One could divide down and use a comparator. Basicaslly slowly tease
the other input of the comparator until it's tripping about half the
time.
If his ADC sample time is fast, he could random or equivalent-time
sample to find the peak. Just make the ADC clock async to the HV
pulse.
Here's the monitor pickoff from my Pockels Cell driver. The pulse is
about 1400v 7ns, sort of half-sine. Could have used a BUF602.
https://www.dropbox.com/scl/fi/8s5xexx4n9i1eyhgxtps8/T850_Pickoff.jpg?rlkey=bsq2uemyy9ijdruiq6lqnwdw0&raw=1
https://www.dropbox.com/scl/fi/rfoqchosbazddbql8smut/DSC02778.JPG?rlkey=wm0k2ys2917n8krscptwvss9p&raw=1
I meant just use comp in place of op-amp in the classic peak hold
circuit. For negative going peaks an open drain comparator makes for
very low parts count :)
Here is what I meant, it gets progressively more accurate at slower dv/dt: >>
Version 4
SHEET 1 880 680
WIRE 16 -32 -416 -32
WIRE -512 32 -512 0
WIRE 16 32 16 -32
WIRE 480 48 64 48
WIRE 128 128 128 96
WIRE 64 144 64 48
WIRE 96 144 64 144
WIRE -512 160 -512 112
WIRE 256 160 160 160
WIRE 384 160 320 160
WIRE 480 160 480 48
WIRE 480 160 384 160
WIRE -416 176 -416 -32
WIRE 16 176 16 112
WIRE 96 176 16 176
WIRE 480 192 480 160
WIRE 16 208 16 176
WIRE 384 208 384 160
WIRE -416 320 -416 256
WIRE 16 320 16 288
WIRE 128 320 128 192
WIRE 384 320 384 272
WIRE 480 320 480 272
FLAG -416 320 0
FLAG -512 160 0
FLAG 128 320 0
FLAG 16 320 0
FLAG 384 320 0
FLAG 480 320 0
FLAG 128 96 P5
FLAG -512 0 P5
FLAG 480 48 OUT
SYMBOL Comparators\\LT1720 128 96 R0
SYMATTR InstName U1
SYMBOL cap 368 208 R0
SYMATTR InstName C1
SYMATTR Value 470p
SYMBOL voltage -512 16 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 5
SYMBOL voltage -416 160 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value SINE(0 500 2meg 0 0 0 0.5)
SYMBOL res 32 128 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R1
SYMATTR Value 199k
SYMBOL res 32 304 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 1k
SYMBOL res 464 176 R0
SYMATTR InstName R3
SYMATTR Value 100k
SYMBOL diode 256 176 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D1
SYMATTR Value 1N4148
TEXT -562 344 Left 2 !.tran 2u
TEXT 376 -144 Left 2 ;EPW SED
TEXT 368 -104 Left 2 ;DEC 2023
TEXT -152 -144 Left 2 ;SHOWING COMPARATOR AS PEAK DET
piglet
Nice sim. Kinda ringy. A bit of resistance in series with C1 might
help.
Open-loop diode into the cap is easier to stabilize.
Or maybe a sample-and-hold approach.
A screaming fast ADC and some FPGA math would be accurate.
fredag den 29. december 2023 kl. 22.10.27 UTC+1 skrev John Larkin:252Fwww.ti.com%252Flit%252Fgpn%252Flmc6482
On Fri, 29 Dec 2023 19:49:01 +0000, piglet <erichp...@hotmail.com>
wrote:
On 29/12/2023 16:27, John Larkin wrote:
On Fri, 29 Dec 2023 08:11:43 +0000, piglet <erichp...@hotmail.com>
wrote:
On 29/12/2023 01:25, Lasse Langwadt Christensen wrote:
fredag den 29. december 2023 kl. 02.11.07 UTC+1 skrev Klaus Kragelund: >> >>>>> Hi
I have a voltage, only present for halfsine peak of 2MHz (500ns wide), which is 500V peak.
I need to know the peak voltage, in an embedded system where the ADC samples at max 5MSa. So way too slow to find the peak.
Figure 7-23 of this datasheet has a classic peak detector:
https://www.ti.com/lit/ds/symlink/lmc6482.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&ts=1703760014317&ref_url=https%253A%252F%252Fwww.ti.com%252Fgeneral%252Fdocs%252Fsuppproductinfo.tsp%253FdistId%253D10%2526gotoUrl%253Dhttps%253A%252F%
overly complicated.
But for a 2MHz signal, I would need a very fast opamp.
I have done simple peak detection, with a diode, and a sample capacitor, followed with an opamp, but nothing is really good.
In this case I have 95k/5k resistor to bring the voltage down to 24V, since then the simple diode drop won't matter much. But 30V opamps are slooooow, so no real good option.
I tried using an emitter follower, but it has a funny peak where the base voltage is higher than the peak voltage, and also has potential to die due to Veb voltage.
One idea I had, use the 24V divider with the diode, then right after the pulse, activate another resistive divider with an FET to bring it to 5V where fast opamps are cheaper. The FET will only turn on as long as to sample the voltage, but seems
Nice sim. Kinda ringy. A bit of resistance in series with C1 might
Any favorite peak detector?
https://www.analog.com/en/design-notes/peak-detectors-gain-in-speed-performance.html ?
Instead of op-amp use a comparator, they are often much faster?
piglet
One could divide down and use a comparator. Basicaslly slowly tease
the other input of the comparator until it's tripping about half the
time.
If his ADC sample time is fast, he could random or equivalent-time
sample to find the peak. Just make the ADC clock async to the HV
pulse.
Here's the monitor pickoff from my Pockels Cell driver. The pulse is
about 1400v 7ns, sort of half-sine. Could have used a BUF602.
https://www.dropbox.com/scl/fi/8s5xexx4n9i1eyhgxtps8/T850_Pickoff.jpg?rlkey=bsq2uemyy9ijdruiq6lqnwdw0&raw=1
https://www.dropbox.com/scl/fi/rfoqchosbazddbql8smut/DSC02778.JPG?rlkey=wm0k2ys2917n8krscptwvss9p&raw=1
I meant just use comp in place of op-amp in the classic peak hold
circuit. For negative going peaks an open drain comparator makes for
very low parts count :)
Here is what I meant, it gets progressively more accurate at slower dv/dt: >> >
Version 4
SHEET 1 880 680
WIRE 16 -32 -416 -32
WIRE -512 32 -512 0
WIRE 16 32 16 -32
WIRE 480 48 64 48
WIRE 128 128 128 96
WIRE 64 144 64 48
WIRE 96 144 64 144
WIRE -512 160 -512 112
WIRE 256 160 160 160
WIRE 384 160 320 160
WIRE 480 160 480 48
WIRE 480 160 384 160
WIRE -416 176 -416 -32
WIRE 16 176 16 112
WIRE 96 176 16 176
WIRE 480 192 480 160
WIRE 16 208 16 176
WIRE 384 208 384 160
WIRE -416 320 -416 256
WIRE 16 320 16 288
WIRE 128 320 128 192
WIRE 384 320 384 272
WIRE 480 320 480 272
FLAG -416 320 0
FLAG -512 160 0
FLAG 128 320 0
FLAG 16 320 0
FLAG 384 320 0
FLAG 480 320 0
FLAG 128 96 P5
FLAG -512 0 P5
FLAG 480 48 OUT
SYMBOL Comparators\\LT1720 128 96 R0
SYMATTR InstName U1
SYMBOL cap 368 208 R0
SYMATTR InstName C1
SYMATTR Value 470p
SYMBOL voltage -512 16 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 5
SYMBOL voltage -416 160 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value SINE(0 500 2meg 0 0 0 0.5)
SYMBOL res 32 128 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R1
SYMATTR Value 199k
SYMBOL res 32 304 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 1k
SYMBOL res 464 176 R0
SYMATTR InstName R3
SYMATTR Value 100k
SYMBOL diode 256 176 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D1
SYMATTR Value 1N4148
TEXT -562 344 Left 2 !.tran 2u
TEXT 376 -144 Left 2 ;EPW SED
TEXT 368 -104 Left 2 ;DEC 2023
TEXT -152 -144 Left 2 ;SHOWING COMPARATOR AS PEAK DET
piglet
help.
Open-loop diode into the cap is easier to stabilize.
Or maybe a sample-and-hold approach.
A screaming fast ADC and some FPGA math would be accurate.
if it is only 2MHz and sine, it wouldn't need to scream that much
On Fri, 29 Dec 2023 11:10:05 -0800 (PST), Fred Bloggs ><bloggs.fredbloggs.fred@gmail.com> wrote:ti.co
On Thursday, December 28, 2023 at 8:11:07?PM UTC-5, Klaus Kragelund wrote: >>> Hi
I have a voltage, only present for halfsine peak of 2MHz (500ns wide), which is 500V peak.
I need to know the peak voltage, in an embedded system where the ADC samples at max 5MSa. So way too slow to find the peak.
Figure 7-23 of this datasheet has a classic peak detector:
https://www.ti.com/lit/ds/symlink/lmc6482.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&ts=1703760014317&ref_url=https%253A%252F%252Fwww.ti.com%252Fgeneral%252Fdocs%252Fsuppproductinfo.tsp%253FdistId%253D10%2526gotoUrl%253Dhttps%253A%252F%252Fwww.
m%252Flit%252Fgpn%252Flmc6482
But for a 2MHz signal, I would need a very fast opamp.
I have done simple peak detection, with a diode, and a sample capacitor, followed with an opamp, but nothing is really good.
In this case I have 95k/5k resistor to bring the voltage down to 24V, since then the simple diode drop won't matter much. But
30V opamps are slooooow, so no real good option.
I tried using an emitter follower, but it has a funny peak where the base voltage is higher than the peak voltage, and also
has potential to die due to Veb voltage.
One idea I had, use the 24V divider with the diode, then right after the pulse, activate another resistive divider with an
FET to bring it to 5V where fast opamps are cheaper. The FET will only turn on as long as to sample the voltage, but seems overly
complicated.
Any favorite peak detector?
Does the peak measurement have to be single-shot or it can it take several cycles? If you want single-shot, it's going to be
pricey. Something like the OPA615 will do it. If you can work with an integrated measurement, it will be 1/3 the cost, something
like the sampling comparator works well many times.
Buffer, peak rectify, calibrate against a good scope.
On Friday, December 29, 2023 at 5:05:07?PM UTC-8, Klaus Kragelund wrote:overly complicated.
On Friday 29 December 2023 at 03:38:56 UTC+1, John Larkin wrote:
On Thu, 28 Dec 2023 17:11:03 -0800 (PST), Klaus Kragelund
<klaus.k...@gmail.com> wrote:
Hi
I have a voltage, only present for halfsine peak of 2MHz (500ns wide), which is 500V peak.
I need to know the peak voltage, in an embedded system where the ADC samples at max 5MSa. So way too slow to find the peak.
One idea I had, use the 24V divider with the diode, then right after the pulse, activate another resistive divider with an FET to bring it to 5V where fast opamps are cheaper. The FET will only turn on as long as to sample the voltage, but seems
100kHzWhat's the pulse reprate?
Any favorite peak detector?
I would like 5%, but may be difficult
Target accuracy?
Sounds dead easy to me; just use a diode-capacitor and when the peak is past, the capacitor IS your peak hold
value;
as long as the event can generate an interrupt to make the ADC do its cycle, that gives you most of
ten microseconds to reset the capacitor before the next peak.
Heck, you could use a calibrated current sink on the hold capacitor and a comparator with 5MHz clock
will resolve about 3% (32 periods full scale) in six of your available 10 us; only takes a counter/timer instead of
the full ADC function. Faster clock would also work...
On a sunny day (Fri, 29 Dec 2023 13:11:46 -0800) it happened John Larkin ><jl@997PotHill.com> wrote in <heduoid3ajbkf7blifo5pm91rj5g77cutv@4ax.com>:ti.co
On Fri, 29 Dec 2023 11:10:05 -0800 (PST), Fred Bloggs >><bloggs.fredbloggs.fred@gmail.com> wrote:
On Thursday, December 28, 2023 at 8:11:07?PM UTC-5, Klaus Kragelund wrote: >>>> Hi
I have a voltage, only present for halfsine peak of 2MHz (500ns wide), which is 500V peak.
I need to know the peak voltage, in an embedded system where the ADC samples at max 5MSa. So way too slow to find the peak.
Figure 7-23 of this datasheet has a classic peak detector:
https://www.ti.com/lit/ds/symlink/lmc6482.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&ts=1703760014317&ref_url=https%253A%252F%252Fwww.ti.com%252Fgeneral%252Fdocs%252Fsuppproductinfo.tsp%253FdistId%253D10%2526gotoUrl%253Dhttps%253A%252F%252Fwww.
m%252Flit%252Fgpn%252Flmc6482
But for a 2MHz signal, I would need a very fast opamp.
I have done simple peak detection, with a diode, and a sample capacitor, followed with an opamp, but nothing is really good.
In this case I have 95k/5k resistor to bring the voltage down to 24V, since then the simple diode drop won't matter much. But
30V opamps are slooooow, so no real good option.
I tried using an emitter follower, but it has a funny peak where the base voltage is higher than the peak voltage, and also
has potential to die due to Veb voltage.
One idea I had, use the 24V divider with the diode, then right after the pulse, activate another resistive divider with an
FET to bring it to 5V where fast opamps are cheaper. The FET will only turn on as long as to sample the voltage, but seems overly
complicated.
Any favorite peak detector?
Does the peak measurement have to be single-shot or it can it take several cycles? If you want single-shot, it's going to be
pricey. Something like the OPA615 will do it. If you can work with an integrated measurement, it will be 1/3 the cost, something
like the sampling comparator works well many times.
Buffer, peak rectify, calibrate against a good scope.
Voltage divider followed by a simple analog video ADC gives
you 8 bit accuracy digital output for digital processing.
Plenty of analog video opamps available too to make a fast peak detector.
It is almost audio so low....
Yes I know, some audiophiles can hear 2 MHz...
Just a voltage divider, diode, capacitor to ground like an AM detector
into his slow ADC is the simplest, no opamp needed!
Need to know more about the application.
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