This could be for anything, but here I'm thinking: most useful for things which deal with analogue audio signals.
Power output transistors, the gain stages before them, tone controls, wherever there are op-amps. Oh, the analogue supply to DAC chips...
The idea: isolate the AC noise on the rail in question (with a capacitor..), use the noise as the control signal of a high-frequency amplifier as, essentially, negative feedback. The amplifier is then connected in reverse phase to the rail so that it counters any AC noise on it with the opposite energy- negating it.
Before this, try to do the best job possible with passive components first (within reason) focusing especially on attenuating the highest frequencies and reducing overall amplitude. Why? So the 180 degree amplifier (TM) {lol...} doesn't have to do this actively (which would increase its cost)
My oscilloscope isn't of the highest frequency variety... When I bought it I wasn't thinking of using it to do work on power supplies. Fortunately, I like to buy nicer things than I need, so I did still get a 200MHz scope. But unfortunately... What I found when I eventually used it to observe some of my many SMPSes, is the bulk of a lot of the noise from the transistor switching is up at 50+ MHz. My excessive scope, was barely excessive enough to register the dang things! Due to this (and my less than ideal leads compounding the problem, probably), I don't have an accurate estimation of the amplitude of these things... Do we only need 50mA to void this crap? If so, this thing could only need to add $20 to the manufacturing of something that includes it.
But if you need a few watts? Now, THAT's going to be a few hundred!
(for 10Ghz BW, which, off the top of my head, should be fast enough for the bulk of these 50-200MHz peaks, but I could be wrong, I'm not an injuneere!)
I assume that the noise is somehow proportional to the current being drawn as the switching transistors switch ( Low power circuit? Low power noise. )
And whatever isn't thrown into the environment by wire induction transmitting it - won't need to be attenuated... But we're not talking long runs of anything inside of amplifiers, probably only traces mere inches in length
How do you feel about this idea? If my first draft implementation is crappy, imagine it's not - what do you think of just the idea itself? Useful?
Question:
Say the +50VDC rail in a class ab amplifier is from a regulated SMPS using standard transistors, and it's capable of up to 5.1A.
The amplifier is outputting 18kHz at 15W. The load on the SMPS looks almost constant due to the 20,000uf audio grade electrolytics buffering the output transistor.
The current at the SMPS output measures 2.0A, voltage ripple is 7mV so we'll pretend it doesn't exist in this situation.
We connect a 4GHz scope on the SMPS output and the AC we see this:
Very simple, the width of the spike is 1ns, the height is 2.3V
Of course we know that we don't need neg 2.3V @ 5A to null this momentary spike, even though it appears to be 52.3V with 5A being drawn. The impedance of the circuit isn't the same at 250MHz, especially just a quarter cycle!
How would we estimate the current required? Is this something that is just... known? Meaning is it known by those who make power supplies how much energy is actually contained within this noise? Like is there a rule, a percentage, something like "if switching at 20% of its maximum rating in the upper kHz-lower MHz range, you take the transistors's maximum rating, divide it by 500 and multiply by 0.2, then you have your answer in mA." something like that? lol
Like I said above, a solution like this doesn't have to cost much if the power required is only in the milliwatt range. Once in the watt range, it looks to me like it'd be getting expensive - that's the impression I got from looking at ready-made solutions on Mouser anyway - for example, a 20MHz to 10GHz amplifier capable of 3 watts costs about $200. If there are cheaper options (discrete gain section after low power, maybe?) that'd be great, but what'd be best is if only milliwatts are needed. And that this is a good idea in the first place lmao!
What do you think?
Power output transistors, the gain stages before them, tone controls, wherever there are op-amps. Oh, the analogue supply to DAC chips...
The idea: isolate the AC noise on the rail in question (with a capacitor..), use the noise as the control signal of a high-frequency amplifier as, essentially, negative feedback. The amplifier is then connected in reverse phase to the rail so that it counters any AC noise on it with the opposite energy- negating it.
Before this, try to do the best job possible with passive components first (within reason) focusing especially on attenuating the highest frequencies and reducing overall amplitude. Why? So the 180 degree amplifier (TM) {lol...} doesn't have to do this actively (which would increase its cost)
My oscilloscope isn't of the highest frequency variety... When I bought it I wasn't thinking of using it to do work on power supplies. Fortunately, I like to buy nicer things than I need, so I did still get a 200MHz scope. But unfortunately... What I found when I eventually used it to observe some of my many SMPSes, is the bulk of a lot of the noise from the transistor switching is up at 50+ MHz. My excessive scope, was barely excessive enough to register the dang things! Due to this (and my less than ideal leads compounding the problem, probably), I don't have an accurate estimation of the amplitude of these things... Do we only need 50mA to void this crap? If so, this thing could only need to add $20 to the manufacturing of something that includes it.
But if you need a few watts? Now, THAT's going to be a few hundred!
(for 10Ghz BW, which, off the top of my head, should be fast enough for the bulk of these 50-200MHz peaks, but I could be wrong, I'm not an injuneere!)
I assume that the noise is somehow proportional to the current being drawn as the switching transistors switch ( Low power circuit? Low power noise. )
And whatever isn't thrown into the environment by wire induction transmitting it - won't need to be attenuated... But we're not talking long runs of anything inside of amplifiers, probably only traces mere inches in length
How do you feel about this idea? If my first draft implementation is crappy, imagine it's not - what do you think of just the idea itself? Useful?
Question:
Say the +50VDC rail in a class ab amplifier is from a regulated SMPS using standard transistors, and it's capable of up to 5.1A.
The amplifier is outputting 18kHz at 15W. The load on the SMPS looks almost constant due to the 20,000uf audio grade electrolytics buffering the output transistor.
The current at the SMPS output measures 2.0A, voltage ripple is 7mV so we'll pretend it doesn't exist in this situation.
We connect a 4GHz scope on the SMPS output and the AC we see this:
Very simple, the width of the spike is 1ns, the height is 2.3V
Of course we know that we don't need neg 2.3V @ 5A to null this momentary spike, even though it appears to be 52.3V with 5A being drawn. The impedance of the circuit isn't the same at 250MHz, especially just a quarter cycle!
How would we estimate the current required? Is this something that is just... known? Meaning is it known by those who make power supplies how much energy is actually contained within this noise? Like is there a rule, a percentage, something like "if switching at 20% of its maximum rating in the upper kHz-lower MHz range, you take the transistors's maximum rating, divide it by 500 and multiply by 0.2, then you have your answer in mA." something like that? lol
Like I said above, a solution like this doesn't have to cost much if the power required is only in the milliwatt range. Once in the watt range, it looks to me like it'd be getting expensive - that's the impression I got from looking at ready-made solutions on Mouser anyway - for example, a 20MHz to 10GHz amplifier capable of 3 watts costs about $200. If there are cheaper options (discrete gain section after low power, maybe?) that'd be great, but what'd be best is if only milliwatts are needed. And that this is a good idea in the first place lmao!
What do you think?
