### Author Topic: Mr. Feedback circuit  (Read 5936 times)

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##### Re: Mr. Feedback circuit
« Reply #8 on: August 31, 2015, 15:19:04 pm »
i have a very strong believe that there is a secret in how the feedbackcoil develop its signal...

i believe it could have being used as a parametric oscilator,,, i mean feeding it with current thru a resistor and having it coupled to the core but not coupled to the flux...

this would be the analog of a condenser microfone ...

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##### Re: Mr. Feedback circuit
« Reply #9 on: August 31, 2015, 18:49:41 pm »
many hours over it today to find out that...

its not a differential amplifier but a difference amplifier with positive feedback so it should latch the pulses with minimal signal in...

basically a comparator.. but the reduced gain increase stability and comom mode noise.. the last is not high depending on how to get the winding and the capacitor,,, the 5 volts  going into the inverting input also brings the circuit side to safe level..

i added a resistor in series with the antiparallel diodes 10 oohm and in series between them and the non inverting input 470... than reducing the capacitor to nf is possible to get 90degrees phase...

i did that to make the feedback of the opamp do its work...

actually the circuit coulbe maybe be left as it is in the patent but that big capacitor on the vic cards is a huge mistake... the 5 volts goes to the inverting input and the rg also to the non inverting input...

I found in simulation the greater is the resistor in series with the input the greater the phase lag... the same is for bigger capacitor and shunt resistor..

if i understood well to keep the commom mode rejection the ratio between r1 and rf must = r2 to
ground

the problem i see with meyer circuit increase with frequency since the reactance of the capcacitor decrease and the resistors in the circuit remain the same...

that why the simple solution is a capacitor that has much greater reactance than the shunt resistance to keep 90dreegree current from voltage but still give enough current so the shunt resistor create enough difference voltage...
the resistor in series in the antiparallel diodes could be not needed... but is interesting to keep r1 and r2 small in theory...

so now let me see iit working

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##### Re: Mr. Feedback circuit
« Reply #10 on: August 31, 2015, 23:15:46 pm »
i got it

the values work 2nf cap in series with 4 turns r1 and r2 10khohm each uf4007antiparallel diodes in parallel with a 220ohm ... having 1mehaohm from out to positive input and connecting 5 volts there too... 1 kiloohm from there to the antiparallel diodes too.. and the rests is just as stan show execpts no center tap...

it lock and the voltage is higher than manually tuning...

this is just thefirst test i did with minimummodifications to my circuit..

as this is to work at lower frequency this values seems okbut i´m reducing input and shunt resistors to get less phase lag

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##### Re: Mr. Feedback circuit
« Reply #11 on: September 01, 2015, 07:17:56 am »
well its locking,,,

as the phase comparator 2 is being used it locks to the minimum frequency... and has 0 degrees of phase diference...

it seems it loosed the ability to follow frequency... it will loose lock and the resonant scanning locks again if in the same range... otherwise an offset is also required to retune to a change in inductor..

maybe there is still phase lag,,, strangely it was able to follow when using a square wave... or when it was not locking to the correct resonant frequency as i described in the first posts...

i also detected some noize in my resonant scanning circuit when the gate is 0% is ok but when the signal goes up to 100% the scanning voltaged get noise... that maybe because i used big resistors... and its on the same board as the gate circuit.. . i will try adding filtering..

I´m thinking that maybe the first phase comparator could be a good idea to be tested.. but my board is little hard to switch to that since i designed it for working with the second comparator...

i´m planning to make a new simplified board for testing..
« Last Edit: September 01, 2015, 08:14:37 am by sebosfato »

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##### Re: Mr. Feedback circuit
« Reply #12 on: September 02, 2015, 18:50:48 pm »
yesterday i was thinking.. hell if i´m getting it to lock why it would loose the lock when circuit parameters change...

after revieweing the pll and finding there were no erros in development... i thohught the only possible reason for it maybe that the capacitor is delaying the signal by 90... so in the end its allways in the end of the lock region somehow... but i thought if i add instead a coil to get this phase correction?

let me see the difference... of course circuit need to change for it a little...

but in my opinion here the current will be just in phase with the pulse being applied so it will sit in the middle of the lock... and the inductors should not contribute to the resonance... and maybe would work as a filter at the same way... also the higher the frequency the better for the inductor... opose to the capacitor case...

http://www.n5dux.com/ham/files/pdf/Phase-Locked%20Loops.pdf

just interesting plls

« Last Edit: September 02, 2015, 19:16:54 pm by sebosfato »

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##### Re: Mr. Feedback circuit
« Reply #13 on: September 04, 2015, 18:16:06 pm »
it worked, however the frequency is little out of the resonance peak by 3khz as there is a small phase difference between the feedback an pulse out...i´m trying to solve that... maybe my only option is a small toroid... with few turns of thick wire... i tried a coil with 22 awg 1mh 1ohm.. so maybe the size of wire messes around...

the resonant freq is 34khz in this case and the pll locks at 37khz...

a comertial capacitor is a better component than a coil regarding power dissipation... maybe thats why the capacitor worked better at first glance.

maybe simply having more turns on the feedback might just work...

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##### Re: Mr. Feedback circuit
« Reply #14 on: September 05, 2015, 07:03:31 am »
oh mAN... The patent circuit is so wrong...

i added two input resistors and now it works much better.. it does not need feedback resistor at least its what seemed to me... i´m trying to get the delay out... now is really very little only 800hz from resonance

the patent shows all that is required to make it work..

the antiparallel diodes

the resistor connecting the positive side to ground...

the other voltage source

but the input resistors are misplaced... should be at the inputs after the antiparallel diodes not before otherwise the feedback can´t do its work correct, at least i guess (even if the internals of the opamp used have antiparallel diodes limiting the input to 1 volt extreme) ...

i added a resistor in parallel with the diodes too to try speeding it up... ( the uf4007 antiparallel diodes)

maybe higher speed diodes would be much better... but here it costs a lot and i have no pair i could use now.. thats why the resistor... to negate the capacitance of the diodes...

i think there is no way to get the pll to show lock condition with phase comparator I since the input and pulses are 90 degress... it would only show locked condition if the pulses are in phase..

this tells the feedback has a secret and i solved a way to get it working correct...

blame on me

instead of voltage i´m getting a sort of current feedback...but 90degress apart... so with the resonance of the vic gets perfect in phase lock..

the nice thing about it is that as my pll is working at the higher freq range the bandwidth is also high so when locks i can vary the ofset and would not even loose lock.. only if get outside the range..

i raised the turns of the feedback as thought before.. and it improoved the phase... so the problems might be the chip having to drive the transistors for the feedback led migh be getting my slew rate down too.. probably would be good to add a buffer...

in a next board i plan to do i will make many real improvements i feel the need to.. like a voltage follower to the filter and other adds raising the stability...

from all that you get that if you get a motivation no pain can stop you!

the 5v i connect to the antiparallel diodes closer to the inverting input... so it kind of tells the chip allong with the 100k resistor on the other input of the opamp to stay down when no signal in..

it was very non intuitive  to exchange the components since both change the phase of current by 90

i just knew that one was positive and other negative..
« Last Edit: September 05, 2015, 09:23:46 am by sebosfato »

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##### Re: Mr. Feedback circuit
« Reply #15 on: September 05, 2015, 09:29:59 am »
if anybody feel greatfull with all this... and feel like could help somehow here is a link for donations..