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Old 27th May 2002, 01:51 AM   #1
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Default 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!

Jocko
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Old 27th May 2002, 02:03 AM   #2
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Question Current source

Isn't the the value of current for the current source verses the change in the value of the DC supply more stable for the circuit with the LED?
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Old 27th May 2002, 02:44 AM   #3
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I thought that was obvious. Someone asked about noise.

Jocko
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Old 27th May 2002, 02:32 PM   #4
CG is offline CG
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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?
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Old 27th May 2002, 02:46 PM   #5
jam is offline jam  United States
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Default The TDR twins don't need any sleep!

CG has a good point about replacing R3 with a current source. Also by how much will the noise increase if the LED was replaced with a Zener? How are the sonics affected?
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Old 27th May 2002, 04:58 PM   #6
tiroth is offline tiroth  United States
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Holy #%@! A schematic from Jocko???

^_^
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Old 27th May 2002, 05:23 PM   #7
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Thumbs up I thought that was obvious

Some more of that EE arogant condensation...... Grey is giong to put you on the list.

H.H.
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Old 28th May 2002, 12:04 AM   #8
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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]

Jocko
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Old 28th May 2002, 11:26 AM   #9
AKSA is offline AKSA  Australia
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Default 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.

Cheers,

Hugh

www.printedelectronics.com
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Old 28th May 2002, 02:10 PM   #10
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Smile hi aksa(hugh)....

check out my submissions on this very idea in peranders thread...''the interesting luxman stage'...
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