Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
On 6/5/19 1:44 am, tabbypurr wrote:
On Sunday, 5 May 2019 04:01:54 UTC+1, Clifford Heath wrote:
On 5/5/19 1:06 am, John Larkin wrote:
What do you do that's so price sensitive?
Do you have a lot of test failures form using reclaimed parts?
I've gleaned that he lives in India, where $15/week is a basic living.
UK. Assembly is dotted about the developing world. At the extreme end some previously made as little as 8-10p a day, under 15 cents.
At that point it's hard to afford enough calories to survive, so..
that's true at 10p a day. Also corn alone does not deliver the right nutrients.
anything that can be scavenged and turned into rupiah can change
someone's life.
Yes, but I do design these things to be reliable, safe & nontoxic, it's not just a free for all. I don't want to create more problems.
Well, kudos for doing something meaningful to improve life in the 3rd
world. You have my respect for it, even if some people would prefer to
bomb them into oblivion or continue to cheat them into eternal servitude
and subordination (as they believe god and Ayn Rand require them to).
Read and comment. AoE x-Chapters,
High-Speed op-amps section, DRAFT.
Recall, the AoE x-Chapters are advanced material that
was meant to come after each relevant chapter, can skip
on a quick first read, go back later for detailed info.
But as main book was growing over 2000 pages, we opted to
bring out main book first, including x-Chapter cross refs,
follow with x-Chapter book. As explained in the preface.
26 pages of good stuff, from new sections 4x.5 and 4x.6
Chapter 4x is to supplement H&H AoE III, chapters 4,5,8.
(Full Chapter 4x is now 146 pages long, still growing.)
DRAFT, but getting close to being complete.
Are explanations excellent, good, OK, or confusing?
Examine tables, any of your favorite parts missing?**
Want a separate low-power table? Can we skip that?
Is the CFB op-amp scene explained well enough?
On 24/4/19 9:04 pm, Winfield Hill wrote:
 Read and comment. AoE x-Chapters,
 High-Speed op-amps section, DRAFT.
 Recall, the AoE x-Chapters are advanced material that
 was meant to come after each relevant chapter, can skip
 on a quick first read, go back later for detailed info.
 But as main book was growing over 2000 pages, we opted to
 bring out main book first, including x-Chapter cross refs,
 follow with x-Chapter book.  As explained in the preface.
 26 pages of good stuff, from new sections 4x.5 and 4x.6
 Chapter 4x is to supplement H&H AoE III, chapters 4,5,8.
 (Full Chapter 4x is now 146 pages long, still growing.)
 DRAFT, but getting close to being complete.
 Are explanations excellent, good, OK, or confusing?
 Examine tables, any of your favorite parts missing?**
 Want a separate low-power table? Can we skip that?
 Is the CFB op-amp scene explained well enough?
Win,
Many thanks for this chapter. Bit surprised to see no mention of the
really fast fully-differential amplifiers, see:
https://www.analog.com/en/products/amplifiers/adc-drivers/fully-differential-amplifiers.html
See e.g. ADL5565, ADA4927-1. The former has -3dB point at 3GHz
On 24/4/19 9:04 pm, Winfield Hill wrote:
Read and comment. AoE x-Chapters,
High-Speed op-amps section, DRAFT.
Recall, the AoE x-Chapters are advanced material that
was meant to come after each relevant chapter, can skip
on a quick first read, go back later for detailed info.
But as main book was growing over 2000 pages, we opted to
bring out main book first, including x-Chapter cross refs,
follow with x-Chapter book. As explained in the preface.
26 pages of good stuff, from new sections 4x.5 and 4x.6
Chapter 4x is to supplement H&H AoE III, chapters 4,5,8.
(Full Chapter 4x is now 146 pages long, still growing.)
DRAFT, but getting close to being complete.
Are explanations excellent, good, OK, or confusing?
Examine tables, any of your favorite parts missing?**
Want a separate low-power table? Can we skip that?
Is the CFB op-amp scene explained well enough?
Win,
Many thanks for this chapter. Bit surprised to see no mention of the
really fast fully-differential amplifiers, see:
https://www.analog.com/en/products/amplifiers/adc-drivers/fully-differential-amplifiers.html
See e.g. ADL5565, ADA4927-1. The former has -3dB point at 3GHz and it's
not the fastest!
Clifford Heath.
"Winfield Hill" wrote in message news:q9pfrl0rmv@drn.newsguy.com...
Are explanations excellent, good, OK, or confusing?
Examine tables, any of your favorite parts missing?**
Want a separate low-power table? Can we skip that?
Is the CFB op-amp scene explained well enough?
Did you like VFB scatterplots? Need some for CFB?
Have a favorite trick that should be included?
Make comments here or send to winfieldhill@yahoo.com
https://www.dropbox.com/s/aemtyly16mtj87n/Op-amps_High-speed_ch4x_DRAFT.pdf?dl=0
Did you see the preview specs for the OPA818? FET-input, e_n = 2.2
nV/âHz at C_in = 2.4 pF (takes ADA4817's crown!) and 1400 V/Âľs slew
rate. 28 mA supply current, though, and decompensated. I might buy some
pre-release samples to test.
On 24.04.19 12:04 PM, Winfield Hill wrote:
https://www.dropbox.com/s/aemtyly16mtj87n/Op-amps_High-speed_ch4x_DRAFT.pdf?dl=0
I'm sure all this will have been found in editing already, but just in case:
â p. 42: "current conveyer" should be "conveyor"
â p. 47: In the ADA4817 note, you are probably referring to output -
input feedback on the ADA4817-1ARDZ (i.e. the SOIC package), right?
"pin-6 feedback" could be a bit more evocative.
- p. 66: Note (x) seems to be missing ("non-inverting input"?)
Did you see the preview specs for the OPA818? FET-input, e_n = 2.2
nV/âHz at C_in = 2.4 pF (takes ADA4817's crown!) and 1400 V/Âľs slew
rate. 28 mA supply current, though, and decompensated. I might buy some
pre-release samples to test.
Did you like VFB scatterplots? Need some for CFB?
The VFB scatterplots are great, but what would be a nice touch would be
to have them in digital form to look up individual points. (One can
always OCR the table, of course.)
â David
"Winfield Hill" wrote in message news:q9pfrl0rmv@drn.newsguy.com...
Are explanations excellent, good, OK, or confusing?
Examine tables, any of your favorite parts missing?**
Want a separate low-power table? Can we skip that?
Is the CFB op-amp scene explained well enough?
Did you like VFB scatterplots? Need some for CFB?
Have a favorite trick that should be included?
https://www.dropbox.com/s/aemtyly16mtj87n/Op-amps_High-speed_ch4x_DRAFT.pdf?dl=0
Well.. The usual... most accounts really are confused
on what the actually fundamental difference is between
CFA and VFA
My take on this is here:
http://www.kevinaylward.co.uk/ee/currentfeedbackmyth/currentfeedbackmyth.xht
To wit, its clear many simply don't understand that the
typically slew speed increase is because of the class
AB input topology, and has, essentially, nothing to do
with the feedback topology at all.
Its worth point out that the name "current feedback"
has been hijacked from its historical definition.
Kevin Aylward wrote...
"Winfield Hill" wrote in message news:q9pfrl0rmv@drn.newsguy.com...
Are explanations excellent, good, OK, or confusing?
Examine tables, any of your favorite parts missing?**
Want a separate low-power table? Can we skip that?
Is the CFB op-amp scene explained well enough?
Did you like VFB scatterplots? Need some for CFB?
Have a favorite trick that should be included?
https://www.dropbox.com/s/aemtyly16mtj87n/Op-amps_High-speed_ch4x_DRAFT.pdf?dl=0
Well.. The usual... most accounts really are confused
on what the actually fundamental difference is between
CFA and VFA
My take on this is here:
http://www.kevinaylward.co.uk/ee/currentfeedbackmyth/currentfeedbackmyth.xht
To wit, its clear many simply don't understand that the
typically slew speed increase is because of the class
AB input topology, and has, essentially, nothing to do
with the feedback topology at all.
Here I take issue, and also agree with you. To me
it's the nature of the VAS, voltage-amplifying-stage.
In the CFB, high error voltages dramatically increase
the VAS high-Z node currents, making for fast slewing.
By contrast, classic VFB stages are struck with their
fixed class-A current. OK, perhaps that's what you're
saying. The counter example is what we like to call
VFB+CFB circuits. Here the CFB "-" input and "feedback"
resistor are buffered with a follower, creating a VFB
amplifier, see 4x.6.3 and Figure 4x.61, panels C and D.
You might note that we called those out in the VFB
table, with note Z. There are quite a few of them,
and they have dramatically-faster slew rates.
One (im)practical consequence of the CFB slew rate advantage is
dramatic loading of the input signal. Instead of being civilized and
adding power gain to go fast, a CFB just steals power from the signal
source.
Am 25.04.19 um 00:42 schrieb Joerg:
On 2019-04-24 14:17, Gerhard Hoffmann wrote:
Am 24.04.19 um 21:35 schrieb Joerg:
1. EMI behavior of opamps. This is generally not understood at all by
engineers and (still!) not taught at universities from what young EEs
told me. A bipolar input stage will rectify RF at the first BE
junction, even stuff at cell phone frequencies. This rectification or
demodulation is very inefficient but since that is inside the loop any
resultying baseband AM will hit at full tilt because it happens at
"open loop".
It's not that FETs are any worse at demodulating than BJTs, it's just
that they need a higher source impedance for the same dBms. Say, a
different cable transformation.
MOSFETs don't demodulate at all because there is no conducting diode
path. I have found cases with hardcore EM susceptibility to the point
where a person outside the concrete walls of the building could upset
a circuit operating at single-digit kHz range, just by turning on
their cell phone. GSM ones were especially bad. After switching to a
CMOS opamp ... nad, zilch, not even when holding a cell phone right
above the open circuit and then turning it on.
Are you really trying to tell me that a thing with a square law transfer
function cannot demodulate? That it takes a PN junction? I've seen it on
BF862 and the opa140 on my table (admittedly open) also dislikes my cell
phone.
For RF in, say, the cell phone range there is no or hardly any loop
gain unless you have a super-fast opamp.
The loop gain is not needed for the RF signal. It's enough if it
exists for the demodulated result of the input square law device.
2. Back-to-back input protection diodes between IN+ and IN-. Very
often overlooked. In datasheets they are sometimes only mentioned in a
footnote under the abs max table but often there is only a +/-0.3V
diff limit. Aside from pouring gasoline on the above mentioned EMI
issue these diodes can really throw people a curve when using opamps
in an unorthodox way or as a comparator. Thou shalt not do that but ...
These diodes are anti-parallel, not an efficient rectifier.
Can be enough. There is always an offset.
100s of mV offset between the input pins of thing designed to have
near infinite gain. OMG.
... It's a very
good thing that they are there. A low noise op amp with zenered BE
junctions at the input is no longer a low noise op amp. And an op amp
with 100 dB open loop gain and a Volt between its inputs is a design
error.
Not if you know what you are doing and the mfg has blessed railing the
output.
Using an op amp as a comparator is not unorthodox, it's wrong.
Nah, BTDT. You have to know the limits and not exceed reverse Vbe
anywhere. Which can be a mere -2V in RF stuff.
The diodes are there to protect other stuff from dying.
Real hot stuff doesn't have diodes. For example the SD5400 quad FET
array, a marvelous IC. One of my circuits almost drove a tech insane
because every one of them he soldered in died. Until I showed him how
to avoid every last bit of ESD. Once inside the circuit everything was
safe.
The data sheet has a different opinion.
http://www.farnell.com/datasheets/69195.pdf
The idea of unprotected MOS gates died mostly with the RCA 40600
(verbatim). It had a nice bronze wire wrapped around its leads, to
be pulled away after soldering. It was soon away from the market
and made place for the 40673, 40841 and 3N140. I still have a few;
they will probably survive me unused in their box.
John Larkin wrote...
One (im)practical consequence of the CFB slew rate advantage is
dramatic loading of the input signal. Instead of being civilized and
adding power gain to go fast, a CFB just steals power from the signal
source.
?? Usually we drive the "+" input, it's the "-"
input that draws current, from the output. Is
the output signal what your complaining about?
On Wed, 24 Apr 2019 15:42:04 -0700, Joerg <news@analogconsultants.com
wrote:
On 2019-04-24 14:17, Gerhard Hoffmann wrote:
Am 24.04.19 um 21:35 schrieb Joerg:
1. EMI behavior of opamps. This is generally not understood at all by
engineers and (still!) not taught at universities from what young EEs
told me. A bipolar input stage will rectify RF at the first BE
junction, even stuff at cell phone frequencies. This rectification or
demodulation is very inefficient but since that is inside the loop any
resultying baseband AM will hit at full tilt because it happens at
"open loop".
It's not that FETs are any worse at demodulating than BJTs, it's just
that they need a higher source impedance for the same dBms. Say, a
different cable transformation.
MOSFETs don't demodulate at all because there is no conducting diode
path. I have found cases with hardcore EM susceptibility to the point
where a person outside the concrete walls of the building could upset a
circuit operating at single-digit kHz range, just by turning on their
cell phone. GSM ones were especially bad. After switching to a CMOS
opamp ... nad, zilch, not even when holding a cell phone right above the
open circuit and then turning it on.
A downside is that one can often not achieve the same low noise
performance with CMOS opamps.
I've been tweaking my 500 MHz triggered Colpitts oscillator [1]. It's
now common-collector, using either a bipolar NPN or an enhancement
phemt. I'm seeing DC effects at startup.
If the device transfer curve is nonlinear upward, which they always
are, an emitter follower can rectify even if there is no base/gate
current. For a largish AC voltage, a mosfet source follower can
rectify. The rectification will be a fraction, a percent maybe, of a
bipolar.
[1] One of the several circuits that I have been futzing with for
years. Turns out that the BFT25 likes to oscillate at un-observable
frequencies in addition to the frequency it was told to oscillate at.
On 2019-05-01 13:08, John Larkin wrote:
On Wed, 24 Apr 2019 15:42:04 -0700, Joerg <news@analogconsultants.com
wrote:
On 2019-04-24 14:17, Gerhard Hoffmann wrote:
Am 24.04.19 um 21:35 schrieb Joerg:
1. EMI behavior of opamps. This is generally not understood at all by
engineers and (still!) not taught at universities from what young EEs
told me. A bipolar input stage will rectify RF at the first BE
junction, even stuff at cell phone frequencies. This rectification or
demodulation is very inefficient but since that is inside the loop any
resultying baseband AM will hit at full tilt because it happens at
"open loop".
It's not that FETs are any worse at demodulating than BJTs, it's just
that they need a higher source impedance for the same dBms. Say, a
different cable transformation.
MOSFETs don't demodulate at all because there is no conducting diode
path. I have found cases with hardcore EM susceptibility to the point
where a person outside the concrete walls of the building could upset a
circuit operating at single-digit kHz range, just by turning on their
cell phone. GSM ones were especially bad. After switching to a CMOS
opamp ... nad, zilch, not even when holding a cell phone right above the
open circuit and then turning it on.
A downside is that one can often not achieve the same low noise
performance with CMOS opamps.
I've been tweaking my 500 MHz triggered Colpitts oscillator [1]. It's
now common-collector, using either a bipolar NPN or an enhancement
phemt. I'm seeing DC effects at startup.
If the device transfer curve is nonlinear upward, which they always
are, an emitter follower can rectify even if there is no base/gate
current. For a largish AC voltage, a mosfet source follower can
rectify. The rectification will be a fraction, a percent maybe, of a
bipolar.
It's many orders of magnitude lower. Switching out a BJT opamp against a
CMOS opamp is among my quickest EMC fixes. Of course, the increased
input noise has to be palatable.
[1] One of the several circuits that I have been futzing with for
years. Turns out that the BFT25 likes to oscillate at un-observable
frequencies in addition to the frequency it was told to oscillate at.
Oh yeah. Without a few ohms or a (very small) ferrite bead in series
with the base they can do a tarantella dance and it can be at
frequencies where the Federales really don't like it. Especially the Air
Force.
On 2019-05-01 09:03, Gerhard Hoffmann wrote:
Am 25.04.19 um 00:42 schrieb Joerg:
On 2019-04-24 14:17, Gerhard Hoffmann wrote:
Am 24.04.19 um 21:35 schrieb Joerg:
1. EMI behavior of opamps. This is generally not understood at all by
engineers and (still!) not taught at universities from what young EEs
told me. A bipolar input stage will rectify RF at the first BE
junction, even stuff at cell phone frequencies. This rectification or
demodulation is very inefficient but since that is inside the loop any
resultying baseband AM will hit at full tilt because it happens at
"open loop".
It's not that FETs are any worse at demodulating than BJTs, it's just
that they need a higher source impedance for the same dBms. Say, a
different cable transformation.
MOSFETs don't demodulate at all because there is no conducting diode
path. I have found cases with hardcore EM susceptibility to the point
where a person outside the concrete walls of the building could upset
a circuit operating at single-digit kHz range, just by turning on
their cell phone. GSM ones were especially bad. After switching to a
CMOS opamp ... nad, zilch, not even when holding a cell phone right
above the open circuit and then turning it on.
Are you really trying to tell me that a thing with a square law transfer
function cannot demodulate? That it takes a PN junction? I've seen it on
BF862 and the opa140 on my table (admittedly open) also dislikes my cell
phone.
Old thread but it could help some younger engineers:
It is all a matter of how much. Works like this: The first BE junction
that RF usually encounters inside an opamp is at the first BJT, first
stage. IN+ as well as IN-. Unfortunately any rectified RF attacks at
full open loop gain.
When replacing it with an opamp with CMOS input any demodulation
mechanism is so inefficient that it the problem typically vanishes
totally. Done it many times and usually some jaws dropped because that
was the simplest EMI fix they ever saw.
GSM phones are particularly bad and I think that is because of the way
they negotiate with a cell tower, starting at full power for whatever
reason. It results in very low frequency pulsing ... WHOPPP .. POP ..
POP .. POP.
For RF in, say, the cell phone range there is no or hardly any loop
gain unless you have a super-fast opamp.
The loop gain is not needed for the RF signal. It's enough if it
exists for the demodulated result of the input square law device.
The problem is that the rectified signal's spectrum can be in the tens
of Hertz, hence full open loop gain. For the LM324 that's a whopping 100dB.
2. Back-to-back input protection diodes between IN+ and IN-. Very
often overlooked. In datasheets they are sometimes only mentioned in a
footnote under the abs max table but often there is only a +/-0.3V
diff limit. Aside from pouring gasoline on the above mentioned EMI
issue these diodes can really throw people a curve when using opamps
in an unorthodox way or as a comparator. Thou shalt not do that but
...
These diodes are anti-parallel, not an efficient rectifier.
Can be enough. There is always an offset.
100s of mV offset between the input pins of thing designed to have
near infinite gain. OMG.
Now look at that at 100dB open loop gain. Less than a millivolt and the
thing can rail.
On 7/13/19 2:37 PM, Joerg wrote:
On 2019-05-01 09:03, Gerhard Hoffmann wrote:
Am 25.04.19 um 00:42 schrieb Joerg:
On 2019-04-24 14:17, Gerhard Hoffmann wrote:
Am 24.04.19 um 21:35 schrieb Joerg:
2. Back-to-back input protection diodes between IN+ and IN-. Very
often overlooked. In datasheets they are sometimes only mentioned
in a
footnote under the abs max table but often there is only a +/-0.3V
diff limit. Aside from pouring gasoline on the above mentioned EMI
issue these diodes can really throw people a curve when using opamps
in an unorthodox way or as a comparator. Thou shalt not do that
but ...
These diodes are anti-parallel, not an efficient rectifier.
Can be enough. There is always an offset.
100s of mV offset between the input pins of thing designed to have
near infinite gain. OMG.
Now look at that at 100dB open loop gain. Less than a millivolt and
the thing can rail.
So colour me stupid. What's so different about offsets due to
rectification vs. intrinsic imbalances, such that they get multiplied by
A_VOL and not A_VCL like all the others?
On 2019-07-13 13:10, Phil Hobbs wrote:
On 7/13/19 2:37 PM, Joerg wrote:
On 2019-05-01 09:03, Gerhard Hoffmann wrote:
Am 25.04.19 um 00:42 schrieb Joerg:
On 2019-04-24 14:17, Gerhard Hoffmann wrote:
Am 24.04.19 um 21:35 schrieb Joerg:
[...]
2. Back-to-back input protection diodes between IN+ and IN-. Very
often overlooked. In datasheets they are sometimes only mentioned
in a
footnote under the abs max table but often there is only a +/-0.3V
diff limit. Aside from pouring gasoline on the above mentioned EMI
issue these diodes can really throw people a curve when using opamps
in an unorthodox way or as a comparator. Thou shalt not do that
but ...
These diodes are anti-parallel, not an efficient rectifier.
Can be enough. There is always an offset.
100s of mV offset between the input pins of thing designed to have
near infinite gain. OMG.
Now look at that at 100dB open loop gain. Less than a millivolt and
the thing can rail.
So colour me stupid. What's so different about offsets due to
rectification vs. intrinsic imbalances, such that they get multiplied by
A_VOL and not A_VCL like all the others?
Imbalances are static, they do not show up as spectrally significant
noise. Rectified RF is not constant and that's the problem. GSM phones
are an extreme case, several watts on-off-on-off-on-off. If you or a
friend have one, turn it off (really off so it has to reboot and seek a
tower, not just the screen), lay it close to the selected audio input
cable of a big stereo, then turn it on. Brace for a really loud
RAT-TAT-TAT sound from the speakers. In the unlikely event that your
stereo doesn't do that send a thank-you note and maybe a gift basket to
their engineers for an excellent job.
CDMA phones like mine (on the Sprint network) do that to a much lesser
extent because their tower negotiation sequence is more efficient.
On 7/13/19 4:26 PM, Joerg wrote:
On 2019-07-13 13:10, Phil Hobbs wrote:
So colour me stupid. What's so different about offsets
due to rectification vs. intrinsic imbalances, such that
they get multiplied by A_VOL and not A_VCL like all the
others?
Imbalances are static, they do not show up as spectrally
significant noise. Rectified RF is not constant and that's
the problem. GSM phones ...
Understood. But unless I misunderstand, you're claiming
that an op amp with A_VCL = 20 dB (say) multiplies the
rectified RF by A_VOL (100 dB) instead. That's what I'm
wondering about.
Am 13.07.19 um 07:18 schrieb David Nadlinger:
Did you see the preview specs for the OPA818? FET-input, e_n = 2.2
nV/âHz at C_in = 2.4 pF (takes ADA4817's crown!) and 1400 V/Âľs slew
rate. 28 mA supply current, though, and decompensated. I might buy
some pre-release samples to test.
I wonder why there is no FET input CFB opamp. Is there a fundamental
problem?
The inputs are dissimilar already, so one could easily reallocate the
inv input FET area to the n.i. side, and its bias current, too.
That should be a 2:1 noise advantage.
The inv. input could be bipolar and minimum size.