Power Supply Noise Rejection Ratio's (PSRR)

Dr.H · 21st July 2005, 03:41 PM

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

Jocko Homo · 21st July 2005, 03:55 PM

Yeah, it is 6 dB.

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

Jocko

Dr.H · 22nd July 2005, 06:57 AM

Hi Jocko,

Yeah, thats what I have heard before. Any data sheets, etc to back-up that claim?

Jocko Homo · 23rd July 2005, 12:01 AM

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

Guido Tent · 23rd July 2005, 09:26 PM

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".

21st July 2005, 03:41 PM	#1
Dr.H diyAudio Member Join Date: Apr 2002	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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21st July 2005, 03:55 PM	#2
Jocko Homo Banned Join Date: Feb 2002 Location: As far from the NOSsers as possible	Yeah, it is 6 dB. At the midpoint when one MOSFET turns off while the other turns on. Jocko

22nd July 2005, 06:57 AM	#3
Dr.H diyAudio Member Join Date: Apr 2002	Hi Jocko, Yeah, thats what I have heard before. Any data sheets, etc to back-up that claim?

23rd July 2005, 12:01 AM	#4
Jocko Homo Banned Join Date: Feb 2002 Location: As far from the NOSsers as possible	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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