Say a weekend project idea, something nice to build

[RoGeorge]

Day1 is done.  Lets see your progress.

I have not even started! 
For the double pendulum, I might probably not have enough mechanical skills.

This weekend I've only followed the very first advice in this thread, and relax.  Previous weekend at least I have had some interesting reading about SMBus controlled batteries, and made a few (failed) attempts to talk with such a battery that still refuses to respond (while other laptop batteries were nice enough to report their parameters by SMBus).  But this weekend, did nothing.

Anybody else happen to have some progress with their projects?  Post some pics please.

[joeqsmith]

Assuming you only have two days, the clocks ticking.

Today I punched out some shims for an experiment I have been working on.
https://www.eevblog.com/forum/rf-microwave/experimenting-with-waveguides-using-the-litevna/msg5506135/#msg5506135

Looking back one year, you can see how seemingly little progress has been. 
https://www.eevblog.com/forum/rf-microwave/experimenting-with-waveguides-using-the-litevna/msg4880348/#msg4880348

[joeqsmith]

Ok, it's been a full weekend.  Lets see the end result. 

[RoGeorge]

No, no, you first! 

[joeqsmith]

Hobby wise,  the only accomplishment was stamping out those shims and setting up the magnetic field for the cavity.  The majority of the weekend was spent doing yard work.   

***
Well, not quite true.  I have been jotting down ideas for a review I am planning on for Lasmux's active probes.   

https://www.eevblog.com/forum/testgear/12-ghz-active-probe-project/

[RAPo]

A video of the output of my gyrator 1ms sweep from 10Hz to 10kHz advanced xy-mode on DHO942s.

Ok, it's been a full weekend.  Lets see the end result.

[mawyatt]

How about a Chaotic Circuit like this, where the two Centroids are Lorenz Attractors.

One can replace the inductor with a Gyrator like we did back in 80s when we were playing around with this for use as an Analog Encryption circuit, Attractors were the "Analog Encryption Keys".

Best,

[RAPo]

Nice work! My real goal is something similar but way more complex: to show 3D-homoclinic bifurcations.
In 1989 I did the [url=https://www.cambridge.org/core/journals/ergodic-theory-and-dynamical-systems/article/homoclinic-points-and-moduli/B78AF9D2DF3B959AB41DA34671B979A0]2D case on paper.

[/url]

How about a Chaotic Circuit like this, where the two Centroids are Lorenz Attractors.

One can replace the inductor with a Gyrator like we did back in 80s when we were playing around with this for use as an Analog Encryption circuit, Attractors were the "Analog Encryption Keys".

Best,

[mawyatt]

For those interested in discrete transistor design, here's an interesting adaptation of the classic Transistor Differential Amplifier. This rendition produces excellent linearity without feedback that we utilized in many of our custom IC developments many decades ago.

Best,

[RoGeorge]

Wow, looks puzzling, thanks! 

I'll have to redraw the schematic, to see if it is related with the Caprio cell.  Thinking about the Caprio cell because you mentioned very low distortions without feedback.

[mawyatt]

This is different than the Caprio Cell which employs a cross coupling technique.

Best,

[mawyatt]

Another fun circuit for the weekend!!

https://www.eevblog.com/forum/testgear/sds800x-hd-actual-use-cases/msg5510188/#msg5510188

Best,

[RoGeorge]

For those interested in discrete transistor design, here's an interesting adaptation of the classic Transistor Differential Amplifier. This rendition produces excellent linearity without feedback that we utilized in many of our custom IC developments many decades ago.

OK, I give up! 
Why does it work?

After looking closely, there's no cross-connection, indeed, so it is not like a Caprio Cell.

Seems to be just a normal differential pair (normal as in symmetric transistors, the pair in the middle of the schematic), with two more differential pairs in which the transistors are strongly asymmetric, and all the three differential pairs are connected in parallel.  I assume 13x means one transistor's area is 13 times bigger, such that the currents ratio is 13:1, right?  And the sum of all bias currents, 11xIb, has to do with the split of 13:1 in the asymmetric pairs, as 13=1+1+11.

How is that suppose to compensate for distortions?   
What is the idea behind splitting the currents in that particular way?


Did some simulations, and tried different asymmetry ratios other than 13x, while keeping the same total 11xIb.



Tried 1, 7, 13 and 20, and indeed, the minimum THD happens around 13x.  Around 13x, the most reduced harmonic is the 3rd one, which is the biggest contributor to the total distortions.  Other harmonics also benefit, but the setup seems to be tuned to reduce the 3rd harmonic in particular.


First 20 harmonics when the area ratio is changed to 1, 7, 13, 20


Detail with the peaks of the 2nd, 3rd, 4th and the 5th harmonic.  Note the red line (corresponding to ratio 13) in the 3rd harmonic is the lowest color at 3kHz.

(Side note, saying around 13x because in my simulation the 13x is the scaling factor for area.  For the splitting of currents to be 13:1, the ratio of areas has to be something like 10...12:1, depending on the transistor model.  If the model is left as generic NPN, the ratio is closer to the ideal split, but for something like a 2N2222 or 2N3905 from the LTspice standard library, the area has to be about 10:1 for the currents ratio to split 13:1.  So, for a 13x current, I should have used a 2N3904 with 11x area, but the fine tuning is not relevant for now.)

- view log (CTRL+L) to inspect the calculated distortions from .fourier ... (minimum THD is for xA=13)
    THD = 1.141442%  when area ratio xA is 1
    THD = 0.106700%  when area ratio xA is 7
    THD = 0.054449%  when area ratio xA is 13  <--- minimum THD at 13:1
    THD = 0.164344%  when area ratio xA is 20

- ako:MODELname in SPICE will retrieve all the parameters of a specified model, yet each parameter can be overwritten selectively, i.e. beta was set to 200

- in the BJT model, the parameters that are scaled by changing the area are:
    IS - Saturation current
    RC - Collector resistance
    RE - Emitter resistance
    RB - Base resistance
    CJE - BE zero-bias junction capacitance
    CJC - BC zero-bias junction capacitance
    CJS - CS zero-bias junction capacitance

[RoGeorge]

My best guess so far, the 2 asymmetric differential pairs were added to straighten the naturally S-like shaped transfer function of the normal (symmetrical) differential pair. 


Image source:  https://en.wikipedia.org/wiki/Differential_amplifier#Long-tailed_pair

Two 13:1 asymmetric pairs, each to correct one end of the S shape.

Though, I wouldn't know how to deduce the 13:1 and the 4+3+4 split of the currents, such that the resulting (combined) transfer function to become less curved.  Is there some easy way to deduce how to split the currents, or the ratios just pop out of math with no intuitive explanation?

[mawyatt]

Having long since forgot how the math worked out, we had a Post Doc Student do it decades ago, and I'm too lazy!!

The concept basically takes the classic diff pair and introduces an offset by means of the area ratio (yes this is area ratio, not current) on each side of the DC transfer curve. The 13 area ratio and the 4 to 3 bias current ratios produce the lowest HD as you've shown.

If you do a DC input sweep and plot the output you will see how the added asymmetrical pairs compensate the center symmetrical pair and "stretch" the input /output linearity range over a simple diff pair. The 3rd Order IMD was almost always our major concern.

We used this and other circuits in our chip design decades ago when extreme dynamic range was in order and at very high frequencies. Imagine what could be done with ~400GHz SiGe transistors

BTW glad you seem to like these circuits & such, and spend the time to dive in and understand!! 

Brings back fond memories of as a young kid (12) mowing grass, painting houses & businesses, repairing stuff, saving lunch money, gambling, whatever to took to save $ to get any test equipment we could find/afford and some tubes & Germanium transistors to build stuff. Wanted to not only look at the theoretical aspects of circuits, but "see" them perform in real life!!

@ RioGeorge with this said, you seem to be a very inquisitive person. Do yourself a favor and get a SDS800X HD, even if you have to eat rice for a month or two (we did while in grad school for a year!!). This little DSO is so darn good that in the hands of someone like yourself will open up new doors to the inner workings and exploration of complex circuits like we've been posting. Go over and look at the stuff we are doing with this here (more to come hopefully, memory is fading fast tho), the Bode and FFT functions alone are worth well more than the scope costs!! 

https://www.eevblog.com/forum/testgear/sds800x-hd-actual-use-cases/

Best,

[mawyatt]

Here's another interesting transistor circuit. This originates from the late Barrie Gilbert Micromixer replacing the transformer with a current commutating quad for the mixing operation.

The circuit fundamentally has unlimited dynamic range as a transimpedance amplifier (Vin to Iout) with ideal transistors. The inductors are for higher frequency work and help reduce noise figure, so can be bypassed for low frequency use.

Note this circuit also behaves as a "pseudo single to differential amplifier", where the input large signal polarity is "steered" to each current output and achieves such without the need for a negative supply by handling negative inputs as currents rather voltages, but without range limits (with ideal devices).

Analysis is quite involved even with such a simple circuit and also achieves a "controlled" range of input impedance as "seen" from the input driving source, an important aspect of controlling linearity at the input.

Anyway, another "fun" circuit to play around with

Best

[temperance]

pseudo single to differential amplifier

Interesting circuit. Can I ask where you found this? Because if I search for the reference you mentioned, the only thing I find are some papers.

Edit:

For those interested in discrete transistor design

Keep em coming. I'm always interested in those things. Today all one can see are IC's talking with IC's. I find that somehow boring.

[mawyatt]

pseudo single to differential amplifier

Interesting circuit. Can I ask where you found this? Because if I search for the reference you mentioned, the only thing I find are some papers.

Edit:

For those interested in discrete transistor design

Keep em coming. I'm always interested in those things. Today all one can see are IC's talking with IC's. I find that somehow boring.

We found this way back in 80~90s and long since forgot where it came from, think it originated with Gilbert tho. We used this as a high dynamic range amplifier and mixer (with commutation).

Best,

[RoGeorge]

introduces an offset by means of the area ratio (yes this is area ratio, not current) on each side of the DC transfer curve

Indeed, I've noticed the TF is shifted, though it seems to be keeping its shape.  I suspect the S shaped TF of the differential pair is not only shaped like an S, but also a Sigmoid function in the mathematical sense.  The Sigmoid shape is one of those function with all kind of strange properties, on par with e^x or with sinusoids.  It was studied a lot recently, since the Sigmoid is the most used shape for the activation function in neural networks, but my math skills are rather low, and never followed the details about the Sigmoid function properties and implications, but I digress.

Yes, I did a brief check in LTspice, to see the difference between a symmetric and asymmetric differential, right after thinking about the approach from my post above.  It was a surprise to see the shape is preserved.  I've looked at the first derivative, too, and that also keeps its shape and symmetry, so it's not that obvious to me what is happening (in the sense that all the hypotheses I've made in advance where not confirmed in simulation).

Will post the simulation anyway, because it's an example of the syntax needed in SPICE when relative area has to be changed.  The simulation uses a SPICE feature named "ako:" (A Kind Of), about which I didn't know before.  AKO allows mass copy of all the parameters of a model, and allows changing only the parameters that need to be overridden.

AKO: is not needed to specify relative area (area is considered by models as a scaling factor, but there is no parameter named "area" in a D or Q model), in the attached example it was used to override the Bf, or to step the trace with transistor's Beta.  In the attached plots only the area ratio is changed, beta was kept 200.


Will visit the topic you linked, and BTW, it was a big need about a topic/book/series/whatever regarding measuring techniques with a recent DSO.  Last book I've seen about that was a book in Italian, and from the tubes era.  Most of the measurements shown in your topic can be applied to other DSO models, too, if not to most of them.  It is always a pleasure to read about such application, but it is so time consuming to write the material.  I have tried a couple of times, but to me it takes forever to make the pics and the text, not to say about formulas, so while it was very fun to measure, it was tedious to document the ideas, e.g.:
- https://www.eevblog.com/forum/projects/measure-a-magnets-b-field-with-a-rigol-ds1054z-oscilloscope-and-a-piece-of-wire/
- https://www.eevblog.com/forum/projects/oscilloscope-with-trace-averaging-as-a-lock-in-amplifier-(rigol-ds1054z)/

Then, after all the time spent documenting, the thread gets lost into a million other threads. 
Maybe I should keep a ToC of titles where I've spent more time. 

[temperance]

Maybe I should keep a ToC of titles where I've spent more time.

That would be great. Interesting stuff and dialogues in those. (The lock in amp for example)

[mawyatt]

Here's an interesting modification to a simple Cascode stage that almost doubles the bandwidth with a single component and doesn't add any addition power consumption nor changes the output amplitude range significantly.

This is a simple simulation with a 2N3904 showing how a selected inductor between the Cascode stages with gain of ~10dBV and improves the BW from ~144MHz to ~265MHz.

What's happening is the shunt capacitance of the top transistor emitter is in parallel with the bottom transistor collector capacitance, this severely limits the overall stage BW. Placing an inductor separates these capacitances and forms a "pi" network with the added inductor, creating a lumped element transmission line equivalent and matching the emitter to collector.

This works, and we used such with 400GHz SiGe devices with on-chip inductors for ultra wide bandwidth applications decades ago.

Best,

[RoGeorge]

For some reason, couldn't leave behind that linearisation technique, had to come up with an intuitive explanation:



TL;DR, adding 3 shifted sigmoid-like shapes, it reduces to adding only 2, because the 3rd is almost flat when far from origin, so it doesn't change much what the middle diff pair will do anyway.  Geometrically, this is like sliding 2 parallel bars, and adding the 3 points marked 1, 2, 3.  The distance between the sliding imaginary bars had to be chosen such that the the moving bars can not fit both on the same side, or else it will worsen the linearity.

In terms of adding slopes, the same, visually is intuitive how adding the intersection between the first derivative, the plot like a hump, and the 2 bars tend to average at a more constant value than the hump variation.  Constant value here corresponds with more constant slope, which corresponds to more linear transfer function, which corresponds to less distortions.


Now, if adding shifted sigmoids reduces distortions, this means the same effect should be achieved no matter how we shift the TF.  Instead of shifting the TF with transistors of a different area, we can use normal differential pairs (transistors of the same area), and shift the transfer function with other methods.  For example with a DC bias. 



 0mV - 0.292460%
 5mV - 0.287210%
10mV - 0.271911%
20mV - 0.217110%
50mV - 0.032649%   <--- min distort 0.03% (+/-50mV value comes from a brief browse, not optimized)
100mV - 0.140207%

The advantage will be that instead of (1+13) + (1+1) + (13+1) = 30 area, same effect can be achieved with 3 equal pairs, all BJT with the same 1x area, so total 6 x area instead of 30, and a 1x area BJT might be faster than a 13x area one, so higher working frequency.

If it were to have more area available, more symmetrical pairs can be paralleled to reduce the noise factor.

Another advantage of symmetrical pairs (DC shifted) is that the overall distortions are lower (at least in simulation) when compared with the same schematic implemented with asymmetrical pairs (see attached FFT detail vs previous FFT detail min THD 0.03% vs. 0.05% w asymmetrical areas).


In case the end application is at low frequency, instead of 3 differential pairs with 3 distinct DC offsets, we can use only one differential pair, and switch the other input with +/-50mV really fast. 



If the switching is at a much higher frequency than the signal, then the output will average the +/-50mV of "shaking", and it will be just like if it were 3 differential pairs instead of just one pair of BJT.  The shaking signal must be averaged out from the output (output must be low pass filtered in case this does not happen naturally).


Even more convenient than that, the above paragraph is nothing but addition (not modulation).  Addition can be made by simply putting the voltage sources in series, or maybe with 2 adding resistors, like in the last draft schematic from the lower right corner.

Note that a shaking made with a sinusoidal HF shaking, instead of square shaking, will still reduce distortions when compared with a normal and not shaken input signal.  (sinusoidal shaking should be easier to implement than square, analysis required for which one linearizes the amplifier better)

Both the adding of the shaking jumps in the input signal, and the low pass filtering of the output if necessary, can be applied outside of an existing amplifier.  The existing amplifier doesn't have to be modified, and doesn't have to be specially designed to include parallel differential pairs, as long as the existing amplifier has enough bandwidth for the fast "shaking" of the useful signal. 


In conclusion, the same core principle of adding shifted transfer functions, can be implemented either:
- by additional asymmetrical differential pairs
- by additional symmetrical differential pairs with different DC offsets
- without additional differential pairs, and instead by time-multiplexing a DC-offset overlapped to the input signal and averaging the amplifier output

First 2 methods will require specialized amplifiers, the 3rd one may be applicable to already existing amplifiers.

[mawyatt]

Have you investigated unequal emitter resistors in the Triplett?

Best,

[RoGeorge]

Interesting idea, I hadn't thought of that.

[RAPo]

An old AEG info center came in. With it you can produce DTMF tones. I've never studied that before. So this weekend will be spent reading about this an Goertzel filters. Mayb there is even some time left to implement decoding DTMF on an Arduino.