Some CCS measurements

Ran some quick tests on CCS using LEDs vs. resistors in the shown circuit.

In brief:

Using R1 w/C1, noise = 4.08 uV. (20 Hz-20kHz)

Using LED w/o C1, noise = 4.73 uV; w/C1, noise = 4.21 uV.

PSRR: LED w/o C1 is 28 dB better than R1 w/o C1. R1 w/C1 is 28 dB better than LED w/o C1. Using C1, both are the same. Increasing value of C1 increases PSRR by amount of increase.

Moral of the story: Bypass!



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2002-05-25 3:45 pm
Thanks for going to all that trouble.

Any guess how much the PSRR would improve if R3 was replaced by a simple CCS (an FET plus resistor)?

Any guess how much the PSRR would improve with a cascode connection (base of cascode device referenced to emitter of CCS)?

Just good guesses here; don't drag out the soldering iron again. Don't you guys ever go to bed?
I am already on the list, aren't I?

I drew the schematic so guys from Pittsburgh would know what I am talking about. Assuming that even I do...........[joke]

Hey jam.......I just made some measurements for you guys to peruse. Why would I want to listen it? Yes, a CCS will improve things, but the whole point was to show what a CCS measures like in the first place. So.......get your simulator and figure it out . Sonnya will help you, if you get stuck. [joke]

CCS refinements

Jocko Homo,

Gratings and connurbations.....

I have done a bit of work on these. Try this.

Split R3 into two equal resistors. Connect C1 from their midpoint to ground.

This is something I saw long ago; it effectively multiplies the effectiveness of C1 for the same capacitance, by increasing the voltage across it, increasing PSRR by greatly increasing the voltage divide fraction.

With the LED, you might drop 2V. Using the split resistor, maybe 6V or even more. I have not PSpiced this (I'd appreciate it if you plugged in the figures; I don't have the program) but I'd expect at least an improvement in PSRR of 6dB.



Hi Mikek,

My sincere thanks. I knew Doug Self wrote of this stuff, that's where I got it from. But I had no idea it was Peter Blomley - a brilliant man! I actually mocked up an Blomley 'crossoverless' Class AB amp once, and it was just wonderfully complex. The ideas behind it were so rich, so intellectually challenging. His Class A Blomley driver regime is another one, very simple, but very effective at scotching crossover from the drivers.

Thanks for filling me in on this.