C-multiplier again

Sorry, the model statement is too long and it wraps. LTspice won't load.

I posted the zip file in abse under the title "MPSA14 Ripple Filter Model"

I checked and it works fine.

Mike

On Mon, 24 May 2010 21:04:19 GMT, Mike <spam@me.not> wrote:

>Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
>
>> On 5/24/2010 8:09 AM, Mike wrote:
>
>[...]
> 
>> Like I said, it's basically C_CE/C_BFC.  You pick a transistor with 
>> reasonable characteristics at frequencies you care about, drive its
>> base from a really really filtered version of V_CC--with a resistor in
>> series to make sure it doesn't oscillate and doesn't blow up if the
>> input or output gets shorted--and put a BFC at the output.  If the
>> transistor has 10 pF C_CB and the BFC is 100 uF, that's 140 dB,
>> provided you look after other stuff such as the Early voltage and the
>> ESR of the output cap. Generally if your application needs more than
>> 100 dB of ripple rejection, you have to be pretty careful.
>> 
>> Cheers
>> 
>> Phil Hobbs
>
>Is that spiceable? I made a simple circuit with a voltage source driving 
>the base and a cap on the emitter. I tried various transistors such as 
>2N2222 and 2N2369, and various ESR and ESL values for the cap. 
>
>The capacitance had little effect on the attenuation floor, but mainly 
>moved the low frequency corner. No reasonable combination of transistors 
>or cap values got below -120dB. The base resistance had little effect. 
>Here's the file if you'd like to show me how it should work:
>
>Version 4
>SHEET 1 1140 1108
>WIRE -304 -448 -384 -448
>WIRE -160 -448 -224 -448
>WIRE -128 -448 -160 -448
>WIRE -128 -400 -128 -448
>WIRE -192 -352 -256 -352
>WIRE -384 -320 -384 -448
>WIRE -256 -320 -256 -352
>WIRE -128 -288 -128 -304
>WIRE -32 -288 -128 -288
>WIRE 16 -288 -32 -288
>WIRE -128 -256 -128 -288
>WIRE -32 -256 -32 -288
>WIRE -384 -224 -384 -240
>WIRE -256 -224 -256 -240
>WIRE -32 -176 -32 -192
>WIRE -128 -160 -128 -176
>WIRE -32 -80 -32 -96
>WIRE -32 16 -32 0
>FLAG -256 -224 0
>FLAG -384 -224 0
>FLAG -128 -160 0
>FLAG -160 -448 Vin
>FLAG -32 -288 Vout
>FLAG -32 16 0
>SYMBOL npn -192 -400 R0
>SYMATTR InstName Q1
>SYMATTR Value 2N2369
>SYMBOL voltage -384 -336 R0
>WINDOW 123 0 0 Left 0
>WINDOW 39 0 0 Left 0
>SYMATTR InstName V1
>SYMATTR Value 15
>SYMBOL voltage -256 -336 R0
>WINDOW 123 0 0 Left 0
>WINDOW 39 24 38 Left 0
>SYMATTR SpiceLine Rser=1
>SYMATTR InstName V2
>SYMATTR Value 10
>SYMBOL current -128 -256 R0
>WINDOW 123 0 0 Left 0
>WINDOW 39 0 0 Left 0
>SYMATTR InstName I1
>SYMATTR Value 20ma
>SYMBOL voltage -208 -448 R90
>WINDOW 0 49 39 VRight 0
>WINDOW 123 -48 40 VRight 0
>WINDOW 39 0 0 Left 0
>SYMATTR InstName V3
>SYMATTR Value2 AC 1
>SYMATTR Value ""
>SYMBOL cap -48 -256 R0
>SYMATTR InstName C1
>SYMATTR Value 1000&#4294967295;f
>SYMATTR SpiceLine Rser=1u Lser=1n
>SYMBOL res -48 -96 R0
>SYMATTR InstName R1
>SYMATTR Value 100m
>SYMBOL ind -48 -192 R0
>SYMATTR InstName L1
>SYMATTR Value 10n
>TEXT -216 -536 Left 0 ;'BJT Ripple Filter
>TEXT -224 -504 Left 0 !.ac oct 100 1 1e7


I did about the same, similar results.

ftp://jjlarkin.lmi.net/C-multiplier.gif

The lf rejection was about 3000:1. The hf rolloff corner corresponds
to a 2 ohm Re and the 15u load cap. The load is only 14 mA, so Re is
relatively high.

My opamp circuit starts with the opamp's roughly 100 dB PSRR and then
hits a 15 ohm + 120 uF lowpass, about 88 Hz corner frequency. That RC
rolloff gets pretty far down before the opamp's PSRR starts to get
bad. And I don't lose the 0.7 volts (or twice that for a darlington)
which happens to matter in my immediate case.

Neither circuit is perfect. There's probably something really good
lurking out in circuit space.

John

On May 25, 10:54=A0am, Mike <s...@me.not> wrote:
> George Herold <gher...@teachspin.com> wrote:
>
> [...]
>
> > Hi Mike, =A0Would you mind telling me how I dump this into LT spice.
> > I=92m not a spice virgin.... but I am still a newlywed.
>
> > Thanks,
>
> > George H.
>
> Hi George - here's how:
>
> 1. Select the listing with your mouse.
> 2. Press Ctrl-C to copy the selected block to the clipboard.
> 3. Open any plain ascii text editor such as NotePad or EditPad.
> 4. Paste the selected text into the word processor with Ctrl-V.
> 5. Use "Save As" to save the file to a suitable folder. Use the file
> =A0 =A0extension ".asc" to run it in LTspice.
> 6. Repeat if there is a plot file, using the ".plt" extension.
>
> If you have installed LTspice and associated the ASC file extension, all
> you need to do is select the file in MS Explorer and it will load the
> file into LTspice.
>
> If you have not associated the file extensions, then load LTspice and use
> the Open File command to locate and run the file.
>
> Please repost if you have any problems.
>
> Mike

Thanks Mike that was easy.... pretty soon I=92ll be ready for the spice
=91Karma Sutra=92.

George H.

"Bitrex" <bitrex@de.lete.earthlink.net> wrote in message 
news:J_-dnXww97pUMGbWnZ2dnUVZ_sadnZ2d@earthlink.com...
> Here's a circuit that lurking in this discussion about voltage regulators 
> inspired me to come up with over the weekend, speaking of useless circuits 
> and audiophools.  It's a voltage regulator that appears to have decent 
> line regulation without any negative feedback. Cuz negative feedback is 
> bad, right?  It's also expensive!
>
> http://i227.photobucket.com/albums/dd240/bitrex2007/voltagereg-1.jpg
>
> Can you see how it works? Or how I think it is intended to work? :) It 
> doesn't really need a split supply, that's just for messing around.  The 
> PSRR is only as good as the output opamp, unfortunately I haven't found a 
> way to get rid of it yet!

Yech, could've saved on a lot of mess by adding an OTA or two.

Considering the multiplier, I would hazard a guess at some overly 
complicated truncated-Taylor-series correction.

It's worth noting that, if Vo is the output, then all the other nodes 
supplied by it inherently have feedback.  In particular, Vref will vary a 
small amount; Vbias will vary proportionally; I_R5 will vary proportionally; 
and there's early effect on all transistors, and PSRR in the multiplier.

With R15 and R19 so excessively large compared to the impedances on the 
other sides (R20 is shunted by D1, and R29 by R18), the OTA offsets will be 
huge, and proportional to I_R6 (hence, OTA).  The first LT1014 sections seem 
to be doing I-to-V conversion, relative to Vbias (a "safe" value, given the 
OTA outputs will work somewhere between Vref and Vo, assuming Vo/2 > ~Vref).

The LHS OTA output is subtracted from Vbias, to which it is relative, so the 
multiplier gets something centered around 0.  This is superfluous, as it has 
differential inputs to begin with.  The RHS OTA gets the same treatment, and 
this zero-referenced value goes to the mult's add input.  Output goes to 
inverting amp to Vo.

Now, LHS OTA has Vref on one side (assuming the zener is actually biased in 
breakdown), and <0V on the other, so it can be simplified as taking Q4 
through a mirror to the IC input.

RHS OTA has a squishy side, and a nearly zero (~6.2mV) not-squishy side. 
I_R6 ~ 0.5mA, so if Q7/Q9 are balanced, they'll see 0.25mA each, and R19 
will see about 2.5uA, dropping 0.25V.  But then it'll be cut off, so it 
won't actually be that far down.  The actual point is somewhere inbetween, 
with Q7 taking more current than Q9.  At any rate, it's still a ratio of 
I_R6.  This is converted to V and added as offset to the product.

So, it looks like milivolt level signals go into and out of the multiplier 
block, R21/R27 and the op-amp pushes it up to useful levels.  Vref has 
little effect, and might be a divider like Vbias, just lower (so the first 
OTA doesn't run out of output range).

There isn't any particular reason for the voltage to be anything at all, 
it's just that, if everything is just so, variation in whatever parameter 
can be made to fall on the vertex of the parabolic transfer curve, having 
zero apparent gain for small values of gain.  This is akin to approximating 
e.g. cos(x) with 1 - x^2/2, which works for small x.  So I was right, it's 
essentially a truncated Taylor series correction.

Tim

-- 
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms 

Tim Williams wrote:
> More ideas.
> 
> Try JFETs.  No Vbe offset = arbitrarily low dropout.  In fact it's negative 
> a lot of the time: even better.  Easy to cascade/cascode.  Use P or N 
> channel, however you want.

Just because V_GS < 0 doesn't mean V_DS < 0.  JFETs fall off a cliff at 
low V_DS, typically well before they get to 0.7V.  BF862s fall off 
starting above 1 V.  They also have far worse Early effect (or the FET 
equivalent, whatever it's called).
> 
> Source terminal is squishy (low Gm).  Solution: servo with op-amp, or if you 
> want to be quirky, add a shunt regulator so the current draw is constant. 
> You're only drawing like 15mA, right?
> 
> Which reminds me of another novel, useless circuit I invented, the shunt 
> current source.
> 
> On my website,
> 
> http://webpages.charter.net/dawill/tmoranwms/Circuits_2010/Shunt_Current_Source.png

Fairly horrible tempco, though, IIUC.

> "This revolutionary (and impressively useless) circuit is the completion of 
> an analogy. Consider: voltage sources are available in two flavors, shunt 
> (e.g., TL431) and series-pass (e.g., LM7805). But current sources are only 
> available in one style, series-pass. These simple circuits complete the 
> analogy, providing a shunt current source. In both cases, a resistor 
> provides a current greater than or equal to the desired output current over 
> the rated range; a current sense resistor, voltage reference and voltage 
> amplifier (VBE and a BJT in the left example; a TL431 and differential pair 
> in the right example) adjust a shunt current to keep the output current 
> constant."
> 
> Man, this whole thing smacks of audiophoolery.  Sometimes, they'll put a CCS 
> into a shunt regulator (even a rather noisy one like a glow discharge tube) 
> just because they feel like it.  Difference being, you can actually measure 
> nanovolts.

You've never designed a high performance photoreceiver, have you?  Noise 
on the bias supply comes in exactly like TIA voltage noise--they're on 
opposite ends of the same capacitor (the photodiode capacitance). 
Achieving nanovolt noise on the supply is very frequently the difference 
between success and failure.

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

George Herold <gherold@teachspin.com> wrote:

[...] 

> Thanks Mike that was easy.... pretty soon I&#4294967295;ll be ready for the spice
> &#4294967295;Karma Sutra&#4294967295;.
> 
> George H.

I forgot to mention - if there is a plot file, it needs the same prefix as 
the asc file. 

Mike

> I did about the same, similar results.
> 
> ftp://jjlarkin.lmi.net/C-multiplier.gif

Phil mentioned many spice programs don't handle this very well. Using the 
data from his later post showed the results with LTspice are not usable.

Mike

On Tue, 25 May 2010 21:48:13 GMT, Mike <spam@me.not> wrote:

>> I did about the same, similar results.
>> 
>> ftp://jjlarkin.lmi.net/C-multiplier.gif
>
>Phil mentioned many spice programs don't handle this very well. Using the 
>data from his later post showed the results with LTspice are not usable.
>
>Mike

The question is whether the Early voltage slope is realistic. I don't
know. I suppose I should breadboard some parts but... the Gerbers are
gone!

John

On Mon, 24 May 2010 23:47:29 -0500, "Tim Williams"
<tmoranwms@charter.net> wrote:

>More ideas.
>
>Try JFETs.  No Vbe offset = arbitrarily low dropout.  In fact it's negative 
>a lot of the time: even better.  Easy to cascade/cascode.  Use P or N 
>channel, however you want.
>
>Source terminal is squishy (low Gm).  Solution: servo with op-amp, or if you 
>want to be quirky, add a shunt regulator so the current draw is constant. 
>You're only drawing like 15mA, right?
>
>Which reminds me of another novel, useless circuit I invented, the shunt 
>current source.
>
>On my website,
>
>http://webpages.charter.net/dawill/tmoranwms/Circuits_2010/Shunt_Current_Source.png
>"This revolutionary (and impressively useless) circuit is the completion of 
>an analogy. Consider: voltage sources are available in two flavors, shunt 
>(e.g., TL431) and series-pass (e.g., LM7805). But current sources are only 
>available in one style, series-pass. These simple circuits complete the 
>analogy, providing a shunt current source. In both cases, a resistor 
>provides a current greater than or equal to the desired output current over 
>the rated range; a current sense resistor, voltage reference and voltage 
>amplifier (VBE and a BJT in the left example; a TL431 and differential pair 
>in the right example) adjust a shunt current to keep the output current 
>constant."

Interesting power dissipation situation. 


I do this occasionally, with transistors or fets:


           Isink
             |
             |
             |
             |
             |
             c
gnd---------b
             e
             |
             |
             |
             R
             |
             |
             |
            -10V



John

Tim Williams wrote:
> "Bitrex" <bitrex@de.lete.earthlink.net> wrote in message 
> news:J_-dnXww97pUMGbWnZ2dnUVZ_sadnZ2d@earthlink.com...
>> Here's a circuit that lurking in this discussion about voltage regulators 
>> inspired me to come up with over the weekend, speaking of useless circuits 
>> and audiophools.  It's a voltage regulator that appears to have decent 
>> line regulation without any negative feedback. Cuz negative feedback is 
>> bad, right?  It's also expensive!
>>
>> http://i227.photobucket.com/albums/dd240/bitrex2007/voltagereg-1.jpg
>>
>> Can you see how it works? Or how I think it is intended to work? :) It 
>> doesn't really need a split supply, that's just for messing around.  The 
>> PSRR is only as good as the output opamp, unfortunately I haven't found a 
>> way to get rid of it yet!
> 
> Yech, could've saved on a lot of mess by adding an OTA or two.
> 
   I just downloaded a model of the LM13700 - I'll test it out.


> Considering the multiplier, I would hazard a guess at some overly 
> complicated truncated-Taylor-series correction.
> 
> It's worth noting that, if Vo is the output, then all the other nodes 
> supplied by it inherently have feedback.  In particular, Vref will vary a 
> small amount; Vbias will vary proportionally; I_R5 will vary proportionally; 
> and there's early effect on all transistors, and PSRR in the multiplier.

   Shhh! :)

> 
> With R15 and R19 so excessively large compared to the impedances on the 
> other sides (R20 is shunted by D1, and R29 by R18), the OTA offsets will be 
> huge, and proportional to I_R6 (hence, OTA).  The first LT1014 sections seem 
> to be doing I-to-V conversion, relative to Vbias (a "safe" value, given the 
> OTA outputs will work somewhere between Vref and Vo, assuming Vo/2 > ~Vref).
> 

  You're right, I missed that.  Those resistors are too large. 
Performance improves when I make them a value that's more in line with 
the impedance on the other side.

> The LHS OTA output is subtracted from Vbias, to which it is relative, so the 
> multiplier gets something centered around 0.  This is superfluous, as it has 
> differential inputs to begin with.  The RHS OTA gets the same treatment, and 
> this zero-referenced value goes to the mult's add input.  Output goes to 
> inverting amp to Vo.

    I had the differential amplifier there because I was messing around 
with scaling factors going into the multiplier.  It turned out to not be 
necessary and the bias voltage can just be applied to pins 2 and 4.

> Now, LHS OTA has Vref on one side (assuming the zener is actually biased in 
> breakdown), and <0V on the other, so it can be simplified as taking Q4 
> through a mirror to the IC input.
> 
> RHS OTA has a squishy side, and a nearly zero (~6.2mV) not-squishy side. 
> I_R6 ~ 0.5mA, so if Q7/Q9 are balanced, they'll see 0.25mA each, and R19 
> will see about 2.5uA, dropping 0.25V.  But then it'll be cut off, so it 
> won't actually be that far down.  The actual point is somewhere inbetween, 
> with Q7 taking more current than Q9.  At any rate, it's still a ratio of 
> I_R6.  This is converted to V and added as offset to the product.
> 
> So, it looks like milivolt level signals go into and out of the multiplier 
> block, R21/R27 and the op-amp pushes it up to useful levels.  Vref has 
> little effect, and might be a divider like Vbias, just lower (so the first 
> OTA doesn't run out of output range).
> 
> There isn't any particular reason for the voltage to be anything at all, 
> it's just that, if everything is just so, variation in whatever parameter 
> can be made to fall on the vertex of the parabolic transfer curve, having 
> zero apparent gain for small values of gain.  This is akin to approximating 
> e.g. cos(x) with 1 - x^2/2, which works for small x.  So I was right, it's 
> essentially a truncated Taylor series correction.
> 

Pretty close - the circuit is in essence an analog computer.  My idea 
was that the transfer function of a differential pair is approximately 
Iout = (Io/2VT)*tanh(vid), where Io is the LTP current.  By selecting 
the V-I converter resistor and Io appropriately you can cause the 
multiplying terms to drop out (at only one temperature, though) and you 
get tanh(vid). This is then squared by the multiplier to get tanh^2. 
The reference voltage is divided down 1000-1 and applied to a similar 
differential pair.

The idea is that the amplified output of the second differential pair 
will be approximately the _derivative_ of the tanh function with respect 
to the reference voltage, or sec^2h(vid), or tanh^2(vid) - 1, which is 
also inverted to get -tanh^2(vid) + 1.  Then it's added in the 
multiplier to cancel the tanh^2 terms and get 1, or a voltage that's 
stable with respect to variations in the reference.  In practice I'm not 
getting 100mv out as I expected but the multiplier does seem to put out 
a stable voltage, with 1V P-P at 1000 Hz bouncing on the supply a FFT on 
the output shows the first harmonic down -115 dB, which is about the 
PSRR of the output op amp.

Whether this is better than just two TL431s set to different voltages 
attached to the inputs of the same op amp as a differential amplifier, I 
do not know. :)


> Tim
>