Power Supply Noise Rejection Ratio's (PSRR) - diyAudio
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Old 21st July 2005, 03:41 PM   #1
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Default Power Supply Noise Rejection Ratio's (PSRR)

Does anyone have access to info on PSRR for logic chips like 74HC74, etc? I have seen suggestions that these figures are as low as 6dB and therefore these chips benefit greatly from the use of clean power supplies.

Can anyone confirm this? Any data I can see?
Thanks
Ryan
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Old 21st July 2005, 03:55 PM   #2
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Yeah, it is 6 dB.

At the midpoint when one MOSFET turns off while the other turns on.

Jocko
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Old 22nd July 2005, 06:57 AM   #3
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Hi Jocko,

Yeah, thats what I have heard before. Any data sheets, etc to back-up that claim?
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Old 23rd July 2005, 12:01 AM   #4
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There are no data sheets to back that up. Just the assumption that the P- and N-channel devices are idntical. If they are not, then it is more than 6 dB in one direction, and much less in the other.

(Hint: It acts like a voltage divider.)

Jocko
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Old 23rd July 2005, 09:26 PM   #5
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Quote:
Originally posted by Jocko Homo
There are no data sheets to back that up. Just the assumption that the P- and N-channel devices are idntical. If they are not, then it is more than 6 dB in one direction, and much less in the other.

(Hint: It acts like a voltage divider.)

Jocko
My measurements on various manufacturers show indeed about 6 dB. Jocko, most outputs are made symmetrical by scaling the FETs such that N and P side become "identical".
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