I'm designing an "overkill" amplifier and am looking to design a ultra high impedance, ultra low noise current source. Right now, it consists of a cascode current mirror using a THAT300/320 transistor array and two green LEDs to set a reference voltage.
My web research has found that use of LEDs to set the current source's reference voltage is about the best one can do to get low noise with a down-side of temperature dependence for actual current.
One question is this: what LEDs are suggested. I've seen references to "rectangular LEDs". Why should they be rectangular?
What would be a good PN choice in surface mount? Why?
My original design used a "filtered" 1N4xxx series "low noise" zener diode, but I found that using said part (without filtering) yielded a noise voltage of 80-100x worse than a junk-box T1-3/4 green led. Even with a "tapped" resistor filter, it was still worse than a LED.
After days of searching for info, I've come up dry. It's time for me to consult the experts! 😀
Thanks,
John
My web research has found that use of LEDs to set the current source's reference voltage is about the best one can do to get low noise with a down-side of temperature dependence for actual current.
One question is this: what LEDs are suggested. I've seen references to "rectangular LEDs". Why should they be rectangular?
What would be a good PN choice in surface mount? Why?
My original design used a "filtered" 1N4xxx series "low noise" zener diode, but I found that using said part (without filtering) yielded a noise voltage of 80-100x worse than a junk-box T1-3/4 green led. Even with a "tapped" resistor filter, it was still worse than a LED.
After days of searching for info, I've come up dry. It's time for me to consult the experts! 😀
Thanks,
John
You should be able to find some pointers in these threads:
http://www.diyaudio.com/forums/showthread.php?threadid=114813
http://www.diyaudio.com/forums/showthread.php?threadid=35821
http://www.diyaudio.com/forums/showthread.php?threadid=114813
http://www.diyaudio.com/forums/showthread.php?threadid=35821
jgedde said:
Simply wrong conception of engineering design - you say you want to maximize 2 parameters while using a topology that requires trading them off against several other unstated constraints
the way to find a acceptable balance is to look at the larger amplifier circuit context to determine which ccs parameters impact the rest of the circuits' performance the most
"the best" off-road truck tire isn't very good on a sprint bicycle
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