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.com%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?
Favorite peak detector?
Started by ●December 28, 2023
Reply by ●December 28, 20232023-12-28
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.ti.com%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?https://www.analog.com/en/design-notes/peak-detectors-gain-in-speed-performance.html ?
Reply by ●December 28, 20232023-12-28
On 12/28/2023 8:11 PM, 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.ti.com%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? >This topology is interesting because it takes the abs of a difference, and has high-impedance inputs. I haven't used it for anything but might be useful for something.. <http://www.seekic.com/uploadfile/ic-circuit/s200971525951166.gif>
Reply by ●December 28, 20232023-12-28
On Thu, 28 Dec 2023 17:11:03 -0800 (PST), Klaus Kragelund <klaus.kragelund@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. > >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.com%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?What's the pulse reprate? Target accuracy? ADC full-scale voltage?
Reply by ●December 28, 20232023-12-28
Klaus Kragelund <klaus.kragelund@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. > > 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.com%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? > >Since the pulse shape is known, I’d tend to use a gated integrator. Much easier. If you don’t know the exact timing, use two slightly wider ones alternating, each with a duty cycle of 75% or so. That way any pulse will be completely inside one or the other. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics
Reply by ●December 28, 20232023-12-28
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.ti.com%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?There was a popular circuit for doing this based on the idea of splitting the input signal into a differentiator that is used to trigger a fast sample and hold at the peak of the original input signal, where the differentiator changes sign...
Reply by ●December 29, 20232023-12-29
On Thursday, December 28, 2023 at 5:11:07 PM UTC-8, 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.ti.com%252Flit%252Fgpn%252Flmc6482 > > 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.
Reply by ●December 29, 20232023-12-29
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.ti.com%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? > > 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
Reply by ●December 29, 20232023-12-29
On Thu, 28 Dec 2023 21:10:39 -0800 (PST), whit3rd <whit3rd@gmail.com> wrote:>On Thursday, December 28, 2023 at 5:11:07?PM UTC-8, 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.ti.com%252Flit%252Fgpn%252Flmc6482 >> >> 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.If the plan is to divide down and peak rectify, a BUF602 is a good part.
Reply by ●December 29, 20232023-12-29
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.ti.com%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? >> >> 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
