So I was out at UB, (picking up some stuff) I was talking with Bruce's* final grad student. He had some success biasing a resistive FIR detector with a current source. The grey haired tech turned him onto an LM134. (A new IC for me too.) http://www.ti.com/lit/ds/symlink/lm134.pdf Apparently they are running it dry down at 1uA and either need more voltage or less current.** (Supply is a 9V alkaline battery.) I don't know what happens when you try to run at less than 1 uA, the spec sheet stops at 10. Anyway I promised a ~100nA and lower design. My first (and only) thought was a voltage reference feeding a big R ... ascci art. Vin----+ Vref +---RRR--+->I out | /| | +----< |-----+ \| But I'm open to other ideas. It needs to be low noise. The LM134 is about 4 times shot noise, so that's a target. First question; How about some other battery. Those 9V transistor batters are noisy. My son uses 2 and 3 cell Lipo's (rechargeable), how are they noise wise? For the opmap I'll need a R-R input I've got opa2192 that should work. Then what voltage reference? I've got REF02's 5V, but they are kinda noisy. Checking AoE3 the LT6654 looks nice, (and not all that spendy) http://cds.linear.com/docs/en/datasheet/6654fh.pdf Is there any reason not to use the 1.25V one? 1.25 V /10Meg is ~ 100nA, and the 100nV/rtHz of noise is 10 fA/rtHz... DC (0.1 - 10 Hz) is ~1uV/10M so 100fA(p-p) Other ideas or comments welcome. Oh the current noise of the R is (1k=4nV/rtHz, 100k = 40, 10M= 400nV = 40 fA/rtHz, the resistor the biggest source. I guess I might gain a little with a 2.5V ref. George H. *Bruce was my post-doc PI (he got the grants) also a good friend. **(They need to run the magnet colder, and that mean the detector is colder, with higher resistance.)
Sub uA battery powered current source.
Started by ●January 10, 2018
Reply by ●January 10, 20182018-01-10
On Wed, 10 Jan 2018 17:21:32 -0800 (PST), George Herold <gherold@teachspin.com> wrote:>So I was out at UB, (picking up some stuff) I was talking with >Bruce's* final grad student. He had some success biasing >a resistive FIR detector with a current source. >The grey haired tech turned him onto an LM134. >(A new IC for me too.) >http://www.ti.com/lit/ds/symlink/lm134.pdf >Apparently they are running it dry down at 1uA >and either need more voltage or less current.** >(Supply is a 9V alkaline battery.) >I don't know what happens when you try to run at >less than 1 uA, the spec sheet stops at 10. > >Anyway I promised a ~100nA and lower design. > >My first (and only) thought was a voltage reference >feeding a big R ... ascci art. > >Vin----+ Vref +---RRR--+->I out > | /| | > +----< |-----+ > \| > >But I'm open to other ideas. >It needs to be low noise. The LM134 is about 4 times >shot noise, so that's a target. > >First question; How about some other battery. Those 9V >transistor batters are noisy. My son uses 2 and 3 cell >Lipo's (rechargeable), how are they noise wise? > >For the opmap I'll need a R-R input I've got opa2192 >that should work. Then what voltage reference? >I've got REF02's 5V, but they are kinda noisy. >Checking AoE3 the LT6654 looks nice, (and not all that spendy) >http://cds.linear.com/docs/en/datasheet/6654fh.pdf > >Is there any reason not to use the 1.25V one? > >1.25 V /10Meg is ~ 100nA, and the 100nV/rtHz of noise is >10 fA/rtHz... DC (0.1 - 10 Hz) is ~1uV/10M so 100fA(p-p) > >Other ideas or comments welcome. > >Oh the current noise of the R is >(1k=4nV/rtHz, 100k = 40, 10M= 400nV = 40 fA/rtHz, the resistor >the biggest source. I guess I might gain a little with a 2.5V ref. > >George H. > > >*Bruce was my post-doc PI (he got the grants) >also a good friend. > >**(They need to run the magnet colder, and that >mean the detector is colder, with higher resistance.)Can you apply a voltage across the detector and measure current? I wonder if a transistor with an emitter resistor would work. The more voltage across the resistor, the lower the Johnson current noise. How much voltage drop will the detector have? -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●January 10, 20182018-01-10
On Wednesday, January 10, 2018 at 8:37:32 PM UTC-5, John Larkin wrote:> On Wed, 10 Jan 2018 17:21:32 -0800 (PST), George Herold > <gherold@teachspin.com> wrote: > > >So I was out at UB, (picking up some stuff) I was talking with > >Bruce's* final grad student. He had some success biasing > >a resistive FIR detector with a current source. > >The grey haired tech turned him onto an LM134. > >(A new IC for me too.) > >http://www.ti.com/lit/ds/symlink/lm134.pdf > >Apparently they are running it dry down at 1uA > >and either need more voltage or less current.** > >(Supply is a 9V alkaline battery.) > >I don't know what happens when you try to run at > >less than 1 uA, the spec sheet stops at 10. > > > >Anyway I promised a ~100nA and lower design. > > > >My first (and only) thought was a voltage reference > >feeding a big R ... ascci art. > > > >Vin----+ Vref +---RRR--+->I out > > | /| | > > +----< |-----+ > > \| > > > >But I'm open to other ideas. > >It needs to be low noise. The LM134 is about 4 times > >shot noise, so that's a target. > > > >First question; How about some other battery. Those 9V > >transistor batters are noisy. My son uses 2 and 3 cell > >Lipo's (rechargeable), how are they noise wise? > > > >For the opmap I'll need a R-R input I've got opa2192 > >that should work. Then what voltage reference? > >I've got REF02's 5V, but they are kinda noisy. > >Checking AoE3 the LT6654 looks nice, (and not all that spendy) > >http://cds.linear.com/docs/en/datasheet/6654fh.pdf > > > >Is there any reason not to use the 1.25V one? > > > >1.25 V /10Meg is ~ 100nA, and the 100nV/rtHz of noise is > >10 fA/rtHz... DC (0.1 - 10 Hz) is ~1uV/10M so 100fA(p-p) > > > >Other ideas or comments welcome. > > > >Oh the current noise of the R is > >(1k=4nV/rtHz, 100k = 40, 10M= 400nV = 40 fA/rtHz, the resistor > >the biggest source. I guess I might gain a little with a 2.5V ref. > > > >George H. > > > > > >*Bruce was my post-doc PI (he got the grants) > >also a good friend. > > > >**(They need to run the magnet colder, and that > >mean the detector is colder, with higher resistance.) > > Can you apply a voltage across the detector and measure current?Sure, the pre-amp would have to be different... At the moment it's a three wire connection to a photoresistor down the bottom of a ~4' probe. liquid He.> > I wonder if a transistor with an emitter resistor would work. The more > voltage across the resistor, the lower the Johnson current noise. How > much voltage drop will the detector have?I think it's about 1-2 Meg ohm at 4.2 K. They need to cool to ~2K, which raises the resistance. (Seems like 1 uA should be low enough.. the grad student might be confused...)> > > > > > -- > > John Larkin Highland Technology, Inc > picosecond timing precision measurement > > jlarkin att highlandtechnology dott com > http://www.highlandtechnology.com
Reply by ●January 10, 20182018-01-10
On Wednesday, January 10, 2018 at 5:21:39 PM UTC-8, George Herold wrote:> The grey haired tech turned him onto an LM134. > (A new IC for me too.) > http://www.ti.com/lit/ds/symlink/lm134.pdf > Apparently they are running it dry down at 1uA > and either need more voltage or less current.** > (Supply is a 9V alkaline battery.)For low noise at low current, bipolars aren't ideal (shot noise). How about the matched MOSFETs from ALD? Cascode current mirror will have good compliance. <http://aldinc.com/pdf/ALD1101.pdf> There's good references with smallish currents, but mainly (because they're bandgap based) there's minimum current 100 uA (TLVH431) and shot noise: you'll want to filter them
Reply by ●January 11, 20182018-01-11
On Wed, 10 Jan 2018 18:05:10 -0800 (PST), George Herold <gherold@teachspin.com> wrote:>On Wednesday, January 10, 2018 at 8:37:32 PM UTC-5, John Larkin wrote: >> On Wed, 10 Jan 2018 17:21:32 -0800 (PST), George Herold >> <gherold@teachspin.com> wrote: >> >> >So I was out at UB, (picking up some stuff) I was talking with >> >Bruce's* final grad student. He had some success biasing >> >a resistive FIR detector with a current source. >> >The grey haired tech turned him onto an LM134. >> >(A new IC for me too.) >> >http://www.ti.com/lit/ds/symlink/lm134.pdf >> >Apparently they are running it dry down at 1uA >> >and either need more voltage or less current.** >> >(Supply is a 9V alkaline battery.) >> >I don't know what happens when you try to run at >> >less than 1 uA, the spec sheet stops at 10. >> > >> >Anyway I promised a ~100nA and lower design. >> > >> >My first (and only) thought was a voltage reference >> >feeding a big R ... ascci art. >> > >> >Vin----+ Vref +---RRR--+->I out >> > | /| | >> > +----< |-----+ >> > \| >> > >> >But I'm open to other ideas. >> >It needs to be low noise. The LM134 is about 4 times >> >shot noise, so that's a target. >> > >> >First question; How about some other battery. Those 9V >> >transistor batters are noisy. My son uses 2 and 3 cell >> >Lipo's (rechargeable), how are they noise wise? >> > >> >For the opmap I'll need a R-R input I've got opa2192 >> >that should work. Then what voltage reference? >> >I've got REF02's 5V, but they are kinda noisy. >> >Checking AoE3 the LT6654 looks nice, (and not all that spendy) >> >http://cds.linear.com/docs/en/datasheet/6654fh.pdf >> > >> >Is there any reason not to use the 1.25V one? >> > >> >1.25 V /10Meg is ~ 100nA, and the 100nV/rtHz of noise is >> >10 fA/rtHz... DC (0.1 - 10 Hz) is ~1uV/10M so 100fA(p-p) >> > >> >Other ideas or comments welcome. >> > >> >Oh the current noise of the R is >> >(1k=4nV/rtHz, 100k = 40, 10M= 400nV = 40 fA/rtHz, the resistor >> >the biggest source. I guess I might gain a little with a 2.5V ref. >> > >> >George H. >> > >> > >> >*Bruce was my post-doc PI (he got the grants) >> >also a good friend. >> > >> >**(They need to run the magnet colder, and that >> >mean the detector is colder, with higher resistance.) >> >> Can you apply a voltage across the detector and measure current? >Sure, the pre-amp would have to be different... At the moment it's >a three wire connection to a photoresistor down the bottom of a >~4' probe. liquid He. >> >> I wonder if a transistor with an emitter resistor would work. The more >> voltage across the resistor, the lower the Johnson current noise. How >> much voltage drop will the detector have? >I think it's about 1-2 Meg ohm at 4.2 K. >They need to cool to ~2K, which raises the resistance. > >(Seems like 1 uA should be low enough.. the grad student might be >confused...) >Why not a power supply and a resistor? -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●January 11, 20182018-01-11
On Wednesday, January 10, 2018 at 5:21:39 PM UTC-8, George Herold wrote:> ...biasing > a resistive FIR detector with a current source. >...down at 1uA > and either need more voltage or less current.** > (Supply is a 9V alkaline battery.)Thinking something like this: <https://www.digikey.com/schemeit/project/low-current-control-SH68M9G30290/> except the single cell battery spozed to be a programmable zener (TLVH431A), and the current mirror shown isn't the cascode that I envisioned, and a capacitor or two would help... and every time I try to edit it, the wires snarl differently. ALD's matched MOS device determines what R2 value biases the '431, and R3 ~= R1 for bias current compensation, and the op amp can be slow but low-noise and low power.
Reply by ●January 11, 20182018-01-11
George Herold wrote...> > Anyway I promised a ~100nA and lower design. > > My first (and only) thought was a voltage reference > feeding a big R ... ascci art. > >Vin----+ Vref +---RRR--+->I out > | /| | > +----< |-----+ > \|That's Figure 13.16 in AOE III. I made one of those as my first bench project at the Institute in 1988. But Figure 13.15 on the next page is more interesting, part of our "Designs by the Masters" series. You can simplify it since you don't need the DAC programming. . ,-- zener ----, . | A2 -in --+----, . +---out +in ---, | . | | Rbias . | | | . | ,------------+ Vminus . | '- -in A1 | . +--- +in out --+---- Vout . | monitor . Iout This circuit has the advantage that it can work up toward the positive rail, without dramatically lowering the zener bias current. The current might instead only double. Only A1 needs to be a good JFET or MOSFET opamp. As for the zener, rather than use a two-terminal IC Vbe reference, etc., to get lower e_n, use a 5.6 or 6.2-volt reference zener, a real zener diode, operating in optimum combo field-effect / zener region, see AoE III page 674. I remember Dave Jones looking for the precision voltage reference in his teardown of a Keithley 5-digit instrument, repeatedly passing over an innocent looking DO-41 glass zener diode, and not realizing that it was the vaunted beast! -- Thanks, - Win
Reply by ●January 11, 20182018-01-11
On Thursday, January 11, 2018 at 12:00:53 AM UTC-5, John Larkin wrote:> On Wed, 10 Jan 2018 18:05:10 -0800 (PST), George Herold > <gherold@teachspin.com> wrote: > > >On Wednesday, January 10, 2018 at 8:37:32 PM UTC-5, John Larkin wrote: > >> On Wed, 10 Jan 2018 17:21:32 -0800 (PST), George Herold > >> <gherold@teachspin.com> wrote: > >> > >> >So I was out at UB, (picking up some stuff) I was talking with > >> >Bruce's* final grad student. He had some success biasing > >> >a resistive FIR detector with a current source. > >> >The grey haired tech turned him onto an LM134. > >> >(A new IC for me too.) > >> >http://www.ti.com/lit/ds/symlink/lm134.pdf > >> >Apparently they are running it dry down at 1uA > >> >and either need more voltage or less current.** > >> >(Supply is a 9V alkaline battery.) > >> >I don't know what happens when you try to run at > >> >less than 1 uA, the spec sheet stops at 10. > >> > > >> >Anyway I promised a ~100nA and lower design. > >> > > >> >My first (and only) thought was a voltage reference > >> >feeding a big R ... ascci art. > >> > > >> >Vin----+ Vref +---RRR--+->I out > >> > | /| | > >> > +----< |-----+ > >> > \| > >> > > >> >But I'm open to other ideas. > >> >It needs to be low noise. The LM134 is about 4 times > >> >shot noise, so that's a target. > >> > > >> >First question; How about some other battery. Those 9V > >> >transistor batters are noisy. My son uses 2 and 3 cell > >> >Lipo's (rechargeable), how are they noise wise? > >> > > >> >For the opmap I'll need a R-R input I've got opa2192 > >> >that should work. Then what voltage reference? > >> >I've got REF02's 5V, but they are kinda noisy. > >> >Checking AoE3 the LT6654 looks nice, (and not all that spendy) > >> >http://cds.linear.com/docs/en/datasheet/6654fh.pdf > >> > > >> >Is there any reason not to use the 1.25V one? > >> > > >> >1.25 V /10Meg is ~ 100nA, and the 100nV/rtHz of noise is > >> >10 fA/rtHz... DC (0.1 - 10 Hz) is ~1uV/10M so 100fA(p-p) > >> > > >> >Other ideas or comments welcome. > >> > > >> >Oh the current noise of the R is > >> >(1k=4nV/rtHz, 100k = 40, 10M= 400nV = 40 fA/rtHz, the resistor > >> >the biggest source. I guess I might gain a little with a 2.5V ref. > >> > > >> >George H. > >> > > >> > > >> >*Bruce was my post-doc PI (he got the grants) > >> >also a good friend. > >> > > >> >**(They need to run the magnet colder, and that > >> >mean the detector is colder, with higher resistance.) > >> > >> Can you apply a voltage across the detector and measure current? > >Sure, the pre-amp would have to be different... At the moment it's > >a three wire connection to a photoresistor down the bottom of a > >~4' probe. liquid He. > >> > >> I wonder if a transistor with an emitter resistor would work. The more > >> voltage across the resistor, the lower the Johnson current noise. How > >> much voltage drop will the detector have? > >I think it's about 1-2 Meg ohm at 4.2 K. > >They need to cool to ~2K, which raises the resistance. > > > >(Seems like 1 uA should be low enough.. the grad student might be > >confused...) > > > > Why not a power supply and a resistor?Yeah that's what they were using. Battery is noisy, so maybe just some filter. Voltage reference and filter? Anyway I promised a current source. George H.> > > -- > > John Larkin Highland Technology, Inc > > lunatic fringe electronics
Reply by ●January 11, 20182018-01-11
On Thursday, January 11, 2018 at 4:02:53 AM UTC-5, whit3rd wrote:> On Wednesday, January 10, 2018 at 5:21:39 PM UTC-8, George Herold wrote: > > ...biasing > > a resistive FIR detector with a current source. > >...down at 1uA > > and either need more voltage or less current.** > > (Supply is a 9V alkaline battery.) > > Thinking something like this: > > <https://www.digikey.com/schemeit/project/low-current-control-SH68M9G30290/> > > except the single cell battery spozed to be a programmable zener (TLVH431A), and the > current mirror shown isn't the cascode that I envisioned, and a capacitor or two > would help... and every time I try to edit it, the wires snarl differently. > > ALD's matched MOS device determines what R2 value biases the '431, > and R3 ~= R1 for bias current compensation, > and the op amp can be slow but low-noise and low power.Scratch, scratch... OK I'm not getting that. Is it like a high side current source. ref-opamp-pfet? George H.
Reply by ●January 11, 20182018-01-11
On Thursday, January 11, 2018 at 6:09:44 AM UTC-5, Winfield Hill wrote:> George Herold wrote... > > > > Anyway I promised a ~100nA and lower design. > > > > My first (and only) thought was a voltage reference > > feeding a big R ... ascci art. > > > >Vin----+ Vref +---RRR--+->I out > > | /| | > > +----< |-----+ > > \| > > That's Figure 13.16 in AOE III. I made one of those > as my first bench project at the Institute in 1988.I found it in the 'circuit ideas' at the end of some chapter in AoE1 or 2. I've used it several times.> But Figure 13.15 on the next page is more interesting, > part of our "Designs by the Masters" series. You can > simplify it since you don't need the DAC programming. > > . ,-- zener ----, > . | A2 -in --+----, > . +---out +in ---, | > . | | Rbias > . | | | > . | ,------------+ Vminus > . | '- -in A1 | > . +--- +in out --+---- Vout > . | monitor > . IoutHuh, OK I'll have to redraw, I was trying to think how to use a shunt reference. Aren't you missing the current setting resistor between out of A2 and (+) in of A1? Hmm where does Vminus come from? (another battery?) I'll probably use a three terminal voltage ref... I've already ordered some LT6654's from DK. Thanks, George H.> > This circuit has the advantage that it can work > up toward the positive rail, without dramatically > lowering the zener bias current. The current > might instead only double. Only A1 needs to be > a good JFET or MOSFET opamp. > > As for the zener, rather than use a two-terminal > IC Vbe reference, etc., to get lower e_n, use a > 5.6 or 6.2-volt reference zener, a real zener > diode, operating in optimum combo field-effect / > zener region, see AoE III page 674. > > I remember Dave Jones looking for the precision > voltage reference in his teardown of a Keithley > 5-digit instrument, repeatedly passing over an > innocent looking DO-41 glass zener diode, and > not realizing that it was the vaunted beast! > > > > -- > Thanks, > - Win
