So I'm doing a new lab amp product.
Our existing one is 500 Hz -- 20 MHz, 1.1 nV/sqrt(Hz).
The new one is aiming to be 10 kHz -- 200 MHz, 0.25 nV/sqrt(Hz). The >spherical cows love it, so we'll see when the test boards arrive later
this week.
As part of the design, I wanted to make an emitter follower with a
decent amount of inductance in series with its tail resistor, to avoid
the transistor turning off on fast negative edges and causing linearity >problems.
Searching on Digikey, I found this very interesting part: ><https://www.digikey.com/en/products/detail/epcos-tdk-electronics/B82498F1472J000/697521>.
4.7 uH 0805 wirewound, with a self-resonant frequency of _210 MHz_,
which is several times higher than many other parts of that description.
That corresponds to an effective parallel capacitance of 0.12 pF,
about that of a resistor of the same size, despite all the copper windings.
Pretty nifty, if true. (Parts on order.)
Cheers
Phil Hobbs
On Tue, 12 Mar 2024 23:17:57 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
So I'm doing a new lab amp product.
Our existing one is 500 Hz -- 20 MHz, 1.1 nV/sqrt(Hz).
The new one is aiming to be 10 kHz -- 200 MHz, 0.25 nV/sqrt(Hz). The
spherical cows love it, so we'll see when the test boards arrive later
this week.
As part of the design, I wanted to make an emitter follower with a
decent amount of inductance in series with its tail resistor, to avoid
the transistor turning off on fast negative edges and causing linearity
problems.
Searching on Digikey, I found this very interesting part:
<https://www.digikey.com/en/products/detail/epcos-tdk-electronics/B82498F1472J000/697521>.
4.7 uH 0805 wirewound, with a self-resonant frequency of _210 MHz_,
which is several times higher than many other parts of that description.
That corresponds to an effective parallel capacitance of 0.12 pF,
about that of a resistor of the same size, despite all the copper windings. >>
Pretty nifty, if true. (Parts on order.)
Cheers
Phil Hobbs
Couldn't you have a high tail voltage and a big resistor, or maybe a
string of smaller inductors? Or something. We've made super wideband inductors from a string of various values.
I'm hassling with inductors now too, but at the other end of the speed spectrum.
We want a programmable inductor, from maybe 1 mH to 500 mH or so,
maybe 100 mA. Sounds like an inductive DAC, a series string of
inductors with shorting relays. If the step inductance ratio were,
say, 1.8:1 we could have some hidden bits, more than the customer
sees, so we could get pretty close to his requested value.
We could test all 2^n steps, make a list, and select the closest to
his request.
We're simulating loads to an engine control computer, torque motors
and solenoids and steppers.
So I'm doing a new lab amp product.
Our existing one is 500 Hz -- 20 MHz, 1.1 nV/sqrt(Hz).
The new one is aiming to be 10 kHz -- 200 MHz, 0.25 nV/sqrt(Hz). The spherical cows love it, so we'll see when the test boards arrive later
this week.
As part of the design, I wanted to make an emitter follower with a
decent amount of inductance in series with its tail resistor, to avoid
the transistor turning off on fast negative edges and causing linearity problems.
Searching on Digikey, I found this very interesting part: <https://www.digikey.com/en/products/detail/epcos-tdk-electronics/B82498F1472J000/697521>.
4.7 uH 0805 wirewound, with a self-resonant frequency of _210 MHz_,
which is several times higher than many other parts of that description.
 That corresponds to an effective parallel capacitance of 0.12 pF,
about that of a resistor of the same size, despite all the copper windings.
Pretty nifty, if true. (Parts on order.)
John Larkin <jl@997PotHill.com> wrote:
On Tue, 12 Mar 2024 23:17:57 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
So I'm doing a new lab amp product.
Our existing one is 500 Hz -- 20 MHz, 1.1 nV/sqrt(Hz).
The new one is aiming to be 10 kHz -- 200 MHz, 0.25 nV/sqrt(Hz). The
spherical cows love it, so we'll see when the test boards arrive later
this week.
As part of the design, I wanted to make an emitter follower with a
decent amount of inductance in series with its tail resistor, to avoid
the transistor turning off on fast negative edges and causing linearity
problems.
Searching on Digikey, I found this very interesting part:
<https://www.digikey.com/en/products/detail/epcos-tdk-electronics/B82498F1472J000/697521>.
4.7 uH 0805 wirewound, with a self-resonant frequency of _210 MHz_,
which is several times higher than many other parts of that description. >>> That corresponds to an effective parallel capacitance of 0.12 pF,
about that of a resistor of the same size, despite all the copper windings. >>>
Pretty nifty, if true. (Parts on order.)
Cheers
Phil Hobbs
Couldn't you have a high tail voltage and a big resistor, or maybe a
string of smaller inductors? Or something. We've made super wideband
inductors from a string of various values.
The first stage (paralleled pHEMTs with a BFU520A cascode and BFU520A >follower) has a gain of about 40 and flatband 1-Hz noise of 0.2 nV. That >means that the noise of the follower and the second stage is not >insignificant.
The second stage is a VCVS active lowpass using an OPA818 at a gain of 10, >and the output stage is an OPA695 CFA inverter, to make the overall circuit >noninverting and provide a gain adjustment. (TE now makes a low-inductance >pot that’s nearly as good as the old Murata PVA2 ones that you use. )
Keeping the supplies simple is important, and so is avoiding ground loops. >The box actually makes +7 and -5 by railsplitting a 24V wall wart, and then >using regulating cap multipliers. (The second and third stages’ supplies
are followers running off the quiet ones, to prevent unwanted feedback.)
Sooo, I want to run the follower on +7/0 if possible, which is where the >inductor comes in. It doesn’t save any power, on account of the >railsplitter, so I can probably use the -5 rail instead.
There’s no overall feedback in this version, because it’s hard to do
without trashing the noise performance and/or stability.
I'm hassling with inductors now too, but at the other end of the speed
spectrum.
We want a programmable inductor, from maybe 1 mH to 500 mH or so,
maybe 100 mA. Sounds like an inductive DAC, a series string of
inductors with shorting relays. If the step inductance ratio were,
say, 1.8:1 we could have some hidden bits, more than the customer
sees, so we could get pretty close to his requested value.
We could test all 2^n steps, make a list, and select the closest to
his request.
We did something similar for choosing resistor taps in a low noise PGA.
Works okay, but is a bit of a pain.
We're simulating loads to an engine control computer, torque motors
and solenoids and steppers.
Fun. Analog computers forever!
Cheers
Phil Hobbs
On 2024-03-13 10:59, John Larkin wrote:
On Wed, 13 Mar 2024 12:49:04 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin <jl@997PotHill.com> wrote:
On Tue, 12 Mar 2024 23:17:57 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
So I'm doing a new lab amp product.
Our existing one is 500 Hz -- 20 MHz, 1.1 nV/sqrt(Hz).
The new one is aiming to be 10 kHz -- 200 MHz, 0.25 nV/sqrt(Hz). The >>>>> spherical cows love it, so we'll see when the test boards arrive later >>>>> this week.
As part of the design, I wanted to make an emitter follower with a
decent amount of inductance in series with its tail resistor, to avoid >>>>> the transistor turning off on fast negative edges and causing linearity >>>>> problems.
Searching on Digikey, I found this very interesting part:
<https://www.digikey.com/en/products/detail/epcos-tdk-electronics/B82498F1472J000/697521>.
4.7 uH 0805 wirewound, with a self-resonant frequency of _210 MHz_,
which is several times higher than many other parts of that description. >>>>> That corresponds to an effective parallel capacitance of 0.12 pF,
about that of a resistor of the same size, despite all the copper windings.
Pretty nifty, if true. (Parts on order.)
Cheers
Phil Hobbs
Couldn't you have a high tail voltage and a big resistor, or maybe a
string of smaller inductors? Or something. We've made super wideband
inductors from a string of various values.
The first stage (paralleled pHEMTs with a BFU520A cascode and BFU520A
follower) has a gain of about 40 and flatband 1-Hz noise of 0.2 nV. That >>> means that the noise of the follower and the second stage is not
insignificant.
The second stage is a VCVS active lowpass using an OPA818 at a gain of 10, >>> and the output stage is an OPA695 CFA inverter, to make the overall circuit >>> noninverting and provide a gain adjustment. (TE now makes a low-inductance >>> pot that’s nearly as good as the old Murata PVA2 ones that you use. )
Keeping the supplies simple is important, and so is avoiding ground loops. >>> The box actually makes +7 and -5 by railsplitting a 24V wall wart, and then >>> using regulating cap multipliers. (The second and third stages’ supplies >>> are followers running off the quiet ones, to prevent unwanted feedback.) >>>
Sooo, I want to run the follower on +7/0 if possible, which is where the >>> inductor comes in. It doesn’t save any power, on account of the
railsplitter, so I can probably use the -5 rail instead.
There’s no overall feedback in this version, because it’s hard to do
without trashing the noise performance and/or stability.
I'm hassling with inductors now too, but at the other end of the speed >>>> spectrum.
We want a programmable inductor, from maybe 1 mH to 500 mH or so,
maybe 100 mA. Sounds like an inductive DAC, a series string of
inductors with shorting relays. If the step inductance ratio were,
say, 1.8:1 we could have some hidden bits, more than the customer
sees, so we could get pretty close to his requested value.
We could test all 2^n steps, make a list, and select the closest to
his request.
We did something similar for choosing resistor taps in a low noise PGA.
Works okay, but is a bit of a pain.
We're simulating loads to an engine control computer, torque motors
and solenoids and steppers.
Fun. Analog computers forever!
Cheers
Phil Hobbs
We are about to publicly announce the P940, our modular power system.
It would be tragic if I make my fortune selling power supplies and
dummy loads that work in the single digits of KHz.
If that happens, I'll commiserate appropriately. ;)
Making DACs with relays is humiliating.
Nah, relays are amazing. There are low-power muxes that come close,
e.g. the TMUX1511 (5 ohms R_on, 2 pF C_off), but nothing that will take
any sort of power.
Of course you can do similar things with tubes. ;)
Cheers
Phil Hobbs
On Wed, 13 Mar 2024 12:49:04 -0000 (UTC), Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin <jl@997PotHill.com> wrote:
On Tue, 12 Mar 2024 23:17:57 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
So I'm doing a new lab amp product.
Our existing one is 500 Hz -- 20 MHz, 1.1 nV/sqrt(Hz).
The new one is aiming to be 10 kHz -- 200 MHz, 0.25 nV/sqrt(Hz). The
spherical cows love it, so we'll see when the test boards arrive later >>>> this week.
As part of the design, I wanted to make an emitter follower with a
decent amount of inductance in series with its tail resistor, to avoid >>>> the transistor turning off on fast negative edges and causing linearity >>>> problems.
Searching on Digikey, I found this very interesting part:
<https://www.digikey.com/en/products/detail/epcos-tdk-electronics/B82498F1472J000/697521>.
4.7 uH 0805 wirewound, with a self-resonant frequency of _210 MHz_,
which is several times higher than many other parts of that description. >>>> That corresponds to an effective parallel capacitance of 0.12 pF,
about that of a resistor of the same size, despite all the copper windings.
Pretty nifty, if true. (Parts on order.)
Cheers
Phil Hobbs
Couldn't you have a high tail voltage and a big resistor, or maybe a
string of smaller inductors? Or something. We've made super wideband
inductors from a string of various values.
The first stage (paralleled pHEMTs with a BFU520A cascode and BFU520A
follower) has a gain of about 40 and flatband 1-Hz noise of 0.2 nV. That
means that the noise of the follower and the second stage is not
insignificant.
The second stage is a VCVS active lowpass using an OPA818 at a gain of 10, >> and the output stage is an OPA695 CFA inverter, to make the overall circuit >> noninverting and provide a gain adjustment. (TE now makes a low-inductance >> pot that’s nearly as good as the old Murata PVA2 ones that you use. )
Keeping the supplies simple is important, and so is avoiding ground loops. >> The box actually makes +7 and -5 by railsplitting a 24V wall wart, and then >> using regulating cap multipliers. (The second and third stages’ supplies >> are followers running off the quiet ones, to prevent unwanted feedback.)
Sooo, I want to run the follower on +7/0 if possible, which is where the
inductor comes in. It doesn’t save any power, on account of the
railsplitter, so I can probably use the -5 rail instead.
There’s no overall feedback in this version, because it’s hard to do
without trashing the noise performance and/or stability.
I'm hassling with inductors now too, but at the other end of the speed
spectrum.
We want a programmable inductor, from maybe 1 mH to 500 mH or so,
maybe 100 mA. Sounds like an inductive DAC, a series string of
inductors with shorting relays. If the step inductance ratio were,
say, 1.8:1 we could have some hidden bits, more than the customer
sees, so we could get pretty close to his requested value.
We could test all 2^n steps, make a list, and select the closest to
his request.
We did something similar for choosing resistor taps in a low noise PGA.
Works okay, but is a bit of a pain.
We're simulating loads to an engine control computer, torque motors
and solenoids and steppers.
Fun. Analog computers forever!
Cheers
Phil Hobbs
We are about to publicly announce the P940, our modular power system.
It would be tragic if I make my fortune selling power supplies and
dummy loads that work in the single digits of KHz.
Making DACs with relays is humiliating.
On Wed, 13 Mar 2024 11:49:31 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
On 2024-03-13 10:59, John Larkin wrote:
On Wed, 13 Mar 2024 12:49:04 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin <jl@997PotHill.com> wrote:
On Tue, 12 Mar 2024 23:17:57 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
So I'm doing a new lab amp product.
Our existing one is 500 Hz -- 20 MHz, 1.1 nV/sqrt(Hz).
The new one is aiming to be 10 kHz -- 200 MHz, 0.25 nV/sqrt(Hz). The >>>>>> spherical cows love it, so we'll see when the test boards arrive later >>>>>> this week.
As part of the design, I wanted to make an emitter follower with a >>>>>> decent amount of inductance in series with its tail resistor, to avoid >>>>>> the transistor turning off on fast negative edges and causing linearity >>>>>> problems.
Searching on Digikey, I found this very interesting part:
<https://www.digikey.com/en/products/detail/epcos-tdk-electronics/B82498F1472J000/697521>.
4.7 uH 0805 wirewound, with a self-resonant frequency of _210 MHz_, >>>>>> which is several times higher than many other parts of that description. >>>>>> That corresponds to an effective parallel capacitance of 0.12 pF,
about that of a resistor of the same size, despite all the copper windings.
Pretty nifty, if true. (Parts on order.)
Cheers
Phil Hobbs
Couldn't you have a high tail voltage and a big resistor, or maybe a >>>>> string of smaller inductors? Or something. We've made super wideband >>>>> inductors from a string of various values.
The first stage (paralleled pHEMTs with a BFU520A cascode and BFU520A
follower) has a gain of about 40 and flatband 1-Hz noise of 0.2 nV. That >>>> means that the noise of the follower and the second stage is not
insignificant.
The second stage is a VCVS active lowpass using an OPA818 at a gain of 10, >>>> and the output stage is an OPA695 CFA inverter, to make the overall circuit
noninverting and provide a gain adjustment. (TE now makes a low-inductance >>>> pot that’s nearly as good as the old Murata PVA2 ones that you use. ) >>>>
Keeping the supplies simple is important, and so is avoiding ground loops. >>>> The box actually makes +7 and -5 by railsplitting a 24V wall wart, and then
using regulating cap multipliers. (The second and third stages’ supplies >>>> are followers running off the quiet ones, to prevent unwanted feedback.) >>>>
Sooo, I want to run the follower on +7/0 if possible, which is where the >>>> inductor comes in. It doesn’t save any power, on account of the
railsplitter, so I can probably use the -5 rail instead.
There’s no overall feedback in this version, because it’s hard to do >>>> without trashing the noise performance and/or stability.
I'm hassling with inductors now too, but at the other end of the speed >>>>> spectrum.
We want a programmable inductor, from maybe 1 mH to 500 mH or so,
maybe 100 mA. Sounds like an inductive DAC, a series string of
inductors with shorting relays. If the step inductance ratio were,
say, 1.8:1 we could have some hidden bits, more than the customer
sees, so we could get pretty close to his requested value.
We could test all 2^n steps, make a list, and select the closest to
his request.
We did something similar for choosing resistor taps in a low noise PGA. >>>> Works okay, but is a bit of a pain.
We're simulating loads to an engine control computer, torque motors
and solenoids and steppers.
Fun. Analog computers forever!
We are about to publicly announce the P940, our modular power system.
It would be tragic if I make my fortune selling power supplies and
dummy loads that work in the single digits of KHz.
If that happens, I'll commiserate appropriately. ;)
Buy me a beer that I can cry in.
Making DACs with relays is humiliating.
Nah, relays are amazing. There are low-power muxes that come close,
e.g. the TMUX1511 (5 ohms R_on, 2 pF C_off), but nothing that will take
any sort of power.
Of course you can do similar things with tubes. ;)
If Ron * Coff is the figure of merit, in femtoseconds, no semi can
come within miles of a relay. We use a $1 DPDT telecom relay that is a
damned good 3 GHz 50 ohm switch.
Tubes don't score well by that standard, except krytrons maybe.
On 2024-03-13 12:04, John Larkin wrote:
On Wed, 13 Mar 2024 11:49:31 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
On 2024-03-13 10:59, John Larkin wrote:
On Wed, 13 Mar 2024 12:49:04 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin <jl@997PotHill.com> wrote:
On Tue, 12 Mar 2024 23:17:57 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
So I'm doing a new lab amp product.
Our existing one is 500 Hz -- 20 MHz, 1.1 nV/sqrt(Hz).
The new one is aiming to be 10 kHz -- 200 MHz, 0.25 nV/sqrt(Hz). The >>>>>>> spherical cows love it, so we'll see when the test boards arrive later >>>>>>> this week.
As part of the design, I wanted to make an emitter follower with a >>>>>>> decent amount of inductance in series with its tail resistor, to avoid >>>>>>> the transistor turning off on fast negative edges and causing linearity >>>>>>> problems.
Searching on Digikey, I found this very interesting part:
<https://www.digikey.com/en/products/detail/epcos-tdk-electronics/B82498F1472J000/697521>.
4.7 uH 0805 wirewound, with a self-resonant frequency of _210 MHz_, >>>>>>> which is several times higher than many other parts of that description.
That corresponds to an effective parallel capacitance of 0.12 pF, >>>>>>> about that of a resistor of the same size, despite all the copper windings.
Pretty nifty, if true. (Parts on order.)
Cheers
Phil Hobbs
Couldn't you have a high tail voltage and a big resistor, or maybe a >>>>>> string of smaller inductors? Or something. We've made super wideband >>>>>> inductors from a string of various values.
The first stage (paralleled pHEMTs with a BFU520A cascode and BFU520A >>>>> follower) has a gain of about 40 and flatband 1-Hz noise of 0.2 nV. That >>>>> means that the noise of the follower and the second stage is not
insignificant.
The second stage is a VCVS active lowpass using an OPA818 at a gain of 10,
and the output stage is an OPA695 CFA inverter, to make the overall circuit
noninverting and provide a gain adjustment. (TE now makes a low-inductance
pot that’s nearly as good as the old Murata PVA2 ones that you use. ) >>>>>
Keeping the supplies simple is important, and so is avoiding ground loops.
The box actually makes +7 and -5 by railsplitting a 24V wall wart, and then
using regulating cap multipliers. (The second and third stages’ supplies >>>>> are followers running off the quiet ones, to prevent unwanted feedback.) >>>>>
Sooo, I want to run the follower on +7/0 if possible, which is where the >>>>> inductor comes in. It doesn’t save any power, on account of the
railsplitter, so I can probably use the -5 rail instead.
There’s no overall feedback in this version, because it’s hard to do >>>>> without trashing the noise performance and/or stability.
I'm hassling with inductors now too, but at the other end of the speed >>>>>> spectrum.
We want a programmable inductor, from maybe 1 mH to 500 mH or so,
maybe 100 mA. Sounds like an inductive DAC, a series string of
inductors with shorting relays. If the step inductance ratio were, >>>>>> say, 1.8:1 we could have some hidden bits, more than the customer
sees, so we could get pretty close to his requested value.
We could test all 2^n steps, make a list, and select the closest to >>>>>> his request.
We did something similar for choosing resistor taps in a low noise PGA. >>>>> Works okay, but is a bit of a pain.
We're simulating loads to an engine control computer, torque motors >>>>>> and solenoids and steppers.
Fun. Analog computers forever!
We are about to publicly announce the P940, our modular power system.
It would be tragic if I make my fortune selling power supplies and
dummy loads that work in the single digits of KHz.
If that happens, I'll commiserate appropriately. ;)
Buy me a beer that I can cry in.
Making DACs with relays is humiliating.
Nah, relays are amazing. There are low-power muxes that come close,
e.g. the TMUX1511 (5 ohms R_on, 2 pF C_off), but nothing that will take
any sort of power.
Of course you can do similar things with tubes. ;)
Not identical things, just similar. Dragging a grid up to +200V quickly
If Ron * Coff is the figure of merit, in femtoseconds, no semi can
come within miles of a relay. We use a $1 DPDT telecom relay that is a
damned good 3 GHz 50 ohm switch.
Tubes don't score well by that standard, except krytrons maybe.
and then leaving it there, with no turn-off charge injection and nearly
no capacitive loading, is a job for a tube. (I used an 811A for that >BITD--it even had a B battery for the plate and a C battery for the grid >bias.) :)
Cheers
Phil Hobbs
I'm hassling with inductors now too, but at the other end of the speed spectrum.
We want a programmable inductor, from maybe 1 mH to 500 mH or so,
maybe 100 mA. Sounds like an inductive DAC, a series string of
inductors with shorting relays. If the step inductance ratio were,
say, 1.8:1 we could have some hidden bits, more than the customer
sees, so we could get pretty close to his requested value.
We could test all 2^n steps, make a list, and select the closest to
his request.
We're simulating loads to an engine control computer, torque motors
and solenoids and steppers.
On 13/03/2024 04:18, John Larkin wrote:
<snip>
I'm hassling with inductors now too, but at the other end of the speed
spectrum.
We want a programmable inductor, from maybe 1 mH to 500 mH or so,
maybe 100 mA. Sounds like an inductive DAC, a series string of
inductors with shorting relays. If the step inductance ratio were,
say, 1.8:1 we could have some hidden bits, more than the customer
sees, so we could get pretty close to his requested value.
We could test all 2^n steps, make a list, and select the closest to
his request.
We're simulating loads to an engine control computer, torque motors
and solenoids and steppers.
Gyrator?
So I'm doing a new lab amp product.
Our existing one is 500 Hz -- 20 MHz, 1.1 nV/sqrt(Hz).
The new one is aiming to be 10 kHz -- 200 MHz, 0.25 nV/sqrt(Hz). The >spherical cows love it, so we'll see when the test boards arrive later
this week.
As part of the design, I wanted to make an emitter follower with a
decent amount of inductance in series with its tail resistor, to avoid
the transistor turning off on fast negative edges and causing linearity >problems.
Searching on Digikey, I found this very interesting part: ><https://www.digikey.com/en/products/detail/epcos-tdk-electronics/B82498F1472J000/697521>.
4.7 uH 0805 wirewound, with a self-resonant frequency of _210 MHz_,
which is several times higher than many other parts of that description.
That corresponds to an effective parallel capacitance of 0.12 pF,
about that of a resistor of the same size, despite all the copper windings.
Pretty nifty, if true. (Parts on order.)
Cheers
Phil Hobbs
On Tue, 12 Mar 2024 23:17:57 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
So I'm doing a new lab amp product.
Our existing one is 500 Hz -- 20 MHz, 1.1 nV/sqrt(Hz).
The new one is aiming to be 10 kHz -- 200 MHz, 0.25 nV/sqrt(Hz). The
spherical cows love it, so we'll see when the test boards arrive later
this week.
As part of the design, I wanted to make an emitter follower with a
decent amount of inductance in series with its tail resistor, to avoid
the transistor turning off on fast negative edges and causing linearity
problems.
Searching on Digikey, I found this very interesting part:
<https://www.digikey.com/en/products/detail/epcos-tdk-electronics/B82498F1472J000/697521>.
4.7 uH 0805 wirewound, with a self-resonant frequency of _210 MHz_,
which is several times higher than many other parts of that description.
That corresponds to an effective parallel capacitance of 0.12 pF,
about that of a resistor of the same size, despite all the copper windings. >>
Pretty nifty, if true. (Parts on order.)
As you say, nifty. Do you have some means of verifying that Fo claim,
Phil? Even a NanoVNA would give a pretty good idea if it's really that
high.
Cursitor Doom <cd@notformail.com> wrote:
On Tue, 12 Mar 2024 23:17:57 -0400, Phil HobbsSure, SRF measurements aren’t super subtle.
<pcdhSpamMeSenseless@electrooptical.net> wrote:
So I'm doing a new lab amp product.
Our existing one is 500 Hz -- 20 MHz, 1.1 nV/sqrt(Hz).
The new one is aiming to be 10 kHz -- 200 MHz, 0.25 nV/sqrt(Hz). The
spherical cows love it, so we'll see when the test boards arrive later
this week.
As part of the design, I wanted to make an emitter follower with a
decent amount of inductance in series with its tail resistor, to avoid
the transistor turning off on fast negative edges and causing linearity
problems.
Searching on Digikey, I found this very interesting part:
<https://www.digikey.com/en/products/detail/epcos-tdk-electronics/B82498F1472J000/697521>.
4.7 uH 0805 wirewound, with a self-resonant frequency of _210 MHz_,
which is several times higher than many other parts of that description. >>> That corresponds to an effective parallel capacitance of 0.12 pF,
about that of a resistor of the same size, despite all the copper windings. >>>
Pretty nifty, if true. (Parts on order.)
As you say, nifty. Do you have some means of verifying that Fo claim,
Phil? Even a NanoVNA would give a pretty good idea if it's really that
high.
Cheers
Phil Hobbs
On Wed, 13 Mar 2024 22:32:27 +0000, Clive Arthur
<clive@nowaytoday.co.uk> wrote:
On 13/03/2024 04:18, John Larkin wrote:
<snip>
I'm hassling with inductors now too, but at the other end of the speed
spectrum.
We want a programmable inductor, from maybe 1 mH to 500 mH or so,
maybe 100 mA. Sounds like an inductive DAC, a series string of
inductors with shorting relays. If the step inductance ratio were,
say, 1.8:1 we could have some hidden bits, more than the customer
sees, so we could get pretty close to his requested value.
We could test all 2^n steps, make a list, and select the closest to
his request.
We're simulating loads to an engine control computer, torque motors
and solenoids and steppers.
Gyrator?
We just yesterday had a brainstorm session about that. How can one
make a programmable electronic fake inductor?
A real inductor stores energy, and can do things like high voltage
flyback. So a fake inductor should store energy, or pretend to. It
could be done with a current shunt, a fast ADC, some math in an FPGA,
a fast DAC, and a big power amplifier with big power supplies. Too
much work.
On 13/03/2024 22:43, john larkin wrote:
On Wed, 13 Mar 2024 22:32:27 +0000, Clive Arthur
<clive@nowaytoday.co.uk> wrote:
On 13/03/2024 04:18, John Larkin wrote:
<snip>
I'm hassling with inductors now too, but at the other end of the speed >>>> spectrum.
We want a programmable inductor, from maybe 1 mH to 500 mH or so,
maybe 100 mA. Sounds like an inductive DAC, a series string of
inductors with shorting relays. If the step inductance ratio were,
say, 1.8:1 we could have some hidden bits, more than the customer
sees, so we could get pretty close to his requested value.
We could test all 2^n steps, make a list, and select the closest to
his request.
We're simulating loads to an engine control computer, torque motors
and solenoids and steppers.
Gyrator?
We just yesterday had a brainstorm session about that. How can one
make a programmable electronic fake inductor?
A real inductor stores energy, and can do things like high voltage
flyback. So a fake inductor should store energy, or pretend to. It
could be done with a current shunt, a fast ADC, some math in an FPGA,
a fast DAC, and a big power amplifier with big power supplies. Too
much work.
Yes, I got part way down the road of designing a gyrator to block
telemetry signals on a power line comms device. Soon realised it would
need lots of power.
Just thinking out loud, and not really a serious suggestion, but would a variac with a fixed inductor on the secondary work as a variable
inductor? I guess 500:1 would be impossible.
On Wed, 13 Mar 2024 22:32:27 +0000, Clive Arthur
<clive@nowaytoday.co.uk> wrote:
On 13/03/2024 04:18, John Larkin wrote:
<snip>
I'm hassling with inductors now too, but at the other end of the speed
spectrum.
We want a programmable inductor, from maybe 1 mH to 500 mH or so,
maybe 100 mA. Sounds like an inductive DAC, a series string of
inductors with shorting relays. If the step inductance ratio were,
say, 1.8:1 we could have some hidden bits, more than the customer
sees, so we could get pretty close to his requested value.
We could test all 2^n steps, make a list, and select the closest to
his request.
We're simulating loads to an engine control computer, torque motors
and solenoids and steppers.
Gyrator?
We just yesterday had a brainstorm session about that. How can one
make a programmable electronic fake inductor?
A real inductor stores energy, and can do things like high voltage
flyback. So a fake inductor should store energy, or pretend to. It
could be done with a current shunt, a fast ADC, some math in an FPGA,
a fast DAC, and a big power amplifier with big power supplies. Too
much work.
On 13/03/2024 22:43, john larkin wrote:
On Wed, 13 Mar 2024 22:32:27 +0000, Clive Arthur
<clive@nowaytoday.co.uk> wrote:
On 13/03/2024 04:18, John Larkin wrote:
<snip>
I'm hassling with inductors now too, but at the other end of the speed >>>> spectrum.
We want a programmable inductor, from maybe 1 mH to 500 mH or so,
maybe 100 mA. Sounds like an inductive DAC, a series string of
inductors with shorting relays. If the step inductance ratio were,
say, 1.8:1 we could have some hidden bits, more than the customer
sees, so we could get pretty close to his requested value.
We could test all 2^n steps, make a list, and select the closest to
his request.
We're simulating loads to an engine control computer, torque motors
and solenoids and steppers.
Gyrator?
We just yesterday had a brainstorm session about that. How can one
make a programmable electronic fake inductor?
A real inductor stores energy, and can do things like high voltage
flyback. So a fake inductor should store energy, or pretend to. It
could be done with a current shunt, a fast ADC, some math in an FPGA,
a fast DAC, and a big power amplifier with big power supplies. Too
much work.
Yes, I got part way down the road of designing a gyrator to block
telemetry signals on a power line comms device. Soon realised it would
need lots of power.
Just thinking out loud, and not really a serious suggestion, but would a >variac with a fixed inductor on the secondary work as a variable
inductor? I guess 500:1 would be impossible.
john larkin <jl@650pot.com> wrote:
On Wed, 13 Mar 2024 22:32:27 +0000, Clive Arthur
<clive@nowaytoday.co.uk> wrote:
On 13/03/2024 04:18, John Larkin wrote:
<snip>
I'm hassling with inductors now too, but at the other end of the speed >>>> spectrum.
We want a programmable inductor, from maybe 1 mH to 500 mH or so,
maybe 100 mA. Sounds like an inductive DAC, a series string of
inductors with shorting relays. If the step inductance ratio were,
say, 1.8:1 we could have some hidden bits, more than the customer
sees, so we could get pretty close to his requested value.
We could test all 2^n steps, make a list, and select the closest to
his request.
We're simulating loads to an engine control computer, torque motors
and solenoids and steppers.
Gyrator?
We just yesterday had a brainstorm session about that. How can one
make a programmable electronic fake inductor?
A real inductor stores energy, and can do things like high voltage
flyback. So a fake inductor should store energy, or pretend to. It
could be done with a current shunt, a fast ADC, some math in an FPGA,
a fast DAC, and a big power amplifier with big power supplies. Too
much work.
I wonder if you could reduce the power supply needs a bit by switchmoding
the incoming current into big storage capacitors so the gyrator does some >energy storage and could make flybacks up to some limit?
On Thu, 14 Mar 2024 13:03:07 -0000 (UTC), piglet
<erichpwagner@hotmail.com> wrote:
john larkin <jl@650pot.com> wrote:
On Wed, 13 Mar 2024 22:32:27 +0000, Clive Arthur
<clive@nowaytoday.co.uk> wrote:
On 13/03/2024 04:18, John Larkin wrote:
<snip>
I'm hassling with inductors now too, but at the other end of the speed >>>>> spectrum.
We want a programmable inductor, from maybe 1 mH to 500 mH or so,
maybe 100 mA. Sounds like an inductive DAC, a series string of
inductors with shorting relays. If the step inductance ratio were,
say, 1.8:1 we could have some hidden bits, more than the customer
sees, so we could get pretty close to his requested value.
We could test all 2^n steps, make a list, and select the closest to
his request.
We're simulating loads to an engine control computer, torque motors
and solenoids and steppers.
Gyrator?
We just yesterday had a brainstorm session about that. How can one
make a programmable electronic fake inductor?
A real inductor stores energy, and can do things like high voltage
flyback. So a fake inductor should store energy, or pretend to. It
could be done with a current shunt, a fast ADC, some math in an FPGA,
a fast DAC, and a big power amplifier with big power supplies. Too
much work.
I wonder if you could reduce the power supply needs a bit by switchmoding >>the incoming current into big storage capacitors so the gyrator does some >>energy storage and could make flybacks up to some limit?
One of my engineers, in her job interview, suggested using a
buck-booster switcher to scale up/down one big inductor. That gives >continuous inductor value tuning. That was clever and got her hired,
but it's probably not practical.
On 13/03/2024 22:43, john larkin wrote:
On Wed, 13 Mar 2024 22:32:27 +0000, Clive Arthur
<clive@nowaytoday.co.uk> wrote:
On 13/03/2024 04:18, John Larkin wrote:
<snip>
I'm hassling with inductors now too, but at the other end of the speed >>>> spectrum.
We want a programmable inductor, from maybe 1 mH to 500 mH or so,
maybe 100 mA. Sounds like an inductive DAC, a series string of
inductors with shorting relays. If the step inductance ratio were,
say, 1.8:1 we could have some hidden bits, more than the customer
sees, so we could get pretty close to his requested value.
We could test all 2^n steps, make a list, and select the closest to
his request.
We're simulating loads to an engine control computer, torque motors
and solenoids and steppers.
Gyrator?
We just yesterday had a brainstorm session about that. How can one
make a programmable electronic fake inductor?
A real inductor stores energy, and can do things like high voltage
flyback. So a fake inductor should store energy, or pretend to. It
could be done with a current shunt, a fast ADC, some math in an FPGA,
a fast DAC, and a big power amplifier with big power supplies. Too
much work.
Yes, I got part way down the road of designing a gyrator to block
telemetry signals on a power line comms device. Soon realised it would
need lots of power.
Just thinking out loud, and not really a serious suggestion, but would a variac with a fixed inductor on the secondary work as a variable
inductor? I guess 500:1 would be impossible.
On 2024-03-14, Clive Arthur <clive@nowaytoday.co.uk> wrote:
On 13/03/2024 22:43, john larkin wrote:
On Wed, 13 Mar 2024 22:32:27 +0000, Clive Arthur
<clive@nowaytoday.co.uk> wrote:
On 13/03/2024 04:18, John Larkin wrote:
<snip>
I'm hassling with inductors now too, but at the other end of the speed >>>>> spectrum.
We want a programmable inductor, from maybe 1 mH to 500 mH or so,
maybe 100 mA. Sounds like an inductive DAC, a series string of
inductors with shorting relays. If the step inductance ratio were,
say, 1.8:1 we could have some hidden bits, more than the customer
sees, so we could get pretty close to his requested value.
We could test all 2^n steps, make a list, and select the closest to
his request.
We're simulating loads to an engine control computer, torque motors
and solenoids and steppers.
Gyrator?
We just yesterday had a brainstorm session about that. How can one
make a programmable electronic fake inductor?
A real inductor stores energy, and can do things like high voltage
flyback. So a fake inductor should store energy, or pretend to. It
could be done with a current shunt, a fast ADC, some math in an FPGA,
a fast DAC, and a big power amplifier with big power supplies. Too
much work.
Yes, I got part way down the road of designing a gyrator to block
telemetry signals on a power line comms device. Soon realised it would
need lots of power.
Just thinking out loud, and not really a serious suggestion, but would a
variac with a fixed inductor on the secondary work as a variable
inductor? I guess 500:1 would be impossible.
it's probably easier to just use the output terminals as a variable inductor.
On Fri, 15 Mar 2024 05:56:38 -0000 (UTC), Jasen Betts <usenet@revmaps.no-ip.org> wrote:
On 2024-03-14, Clive Arthur <clive@nowaytoday.co.uk> wrote:
On 13/03/2024 22:43, john larkin wrote:
On Wed, 13 Mar 2024 22:32:27 +0000, Clive Arthur
<clive@nowaytoday.co.uk> wrote:
On 13/03/2024 04:18, John Larkin wrote:
Just thinking out loud, and not really a serious suggestion, but would a >>> variac with a fixed inductor on the secondary work as a variable
inductor? I guess 500:1 would be impossible.
it's probably easier to just use the output terminals as a variable inductor.
I need a surface-mount motorized variac!
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