In Valve Ampifiers 4th ed. page 138, in the section on PSRR of the differential amplifiers he states that:
"Since hum and noise on the power supply line are a common-mode signal, they must also be attenuated by the CMRR. We might also expect the potential divider formed by ra and RL to give significant additional attenuation...the attenuation of power supply noise (solely due to potential divider action) is thus:
Attenuation = (RL+2ra)/[2(RL+2ra)] = <6dB.
If RL>>ra, we achieve the maximum attenuation of 6 dB!...It is now well worth comparing the PSRR of the common cathode stage, μ-follower and differential pair... The differential pair is the best and will remain the best"
Am I missing something or is the whole section confusing PSRR with CMRR? I was under the impression the PSRR of a differential pair is basically zero (all PSU noise appears at the outputs), nowhere near 6dB. What is Jones talking about?
"Since hum and noise on the power supply line are a common-mode signal, they must also be attenuated by the CMRR. We might also expect the potential divider formed by ra and RL to give significant additional attenuation...the attenuation of power supply noise (solely due to potential divider action) is thus:
Attenuation = (RL+2ra)/[2(RL+2ra)] = <6dB.
If RL>>ra, we achieve the maximum attenuation of 6 dB!...It is now well worth comparing the PSRR of the common cathode stage, μ-follower and differential pair... The differential pair is the best and will remain the best"
Am I missing something or is the whole section confusing PSRR with CMRR? I was under the impression the PSRR of a differential pair is basically zero (all PSU noise appears at the outputs), nowhere near 6dB. What is Jones talking about?
PSRR is peculiar form of common mode signal. But in place of appearing through signal line, it does at the power source ones.
But he's talking specifically about the PSRR of the diff amp itself, not the additional CMRR of the output stage or whatever
It depends crucially on where you take the output. If you look at Terman and all the others from that era, it was always assumed that the output was taken differentially. In which case, PSRR = CMRR. But if you want to argue that isn't realistic, and that each output should be referenced to 0V, then I would agree with you, but it has been convention for over seventy years and it's quite difficult overturning conventions. The point was covered at ETF2017 for which a Powerpoint 2003 file is attached. The file has been renamed with .txt extension because it was ignored with its .ppt extension, so download, change its name back and find an older operating system prepared to acknowledge it.
Do you know that W10 lets you rename it anything you like, including extensions, but still think it's a txt file? Damn you Bill gates!
Jan
Jan
Windows follies....
I'm using Chrome as my browser, in Win11.
I clicked on the file Morgan uploaded, and when the "Save As" dialog box opened, I renamed the file ETF2017.ppt.
That got saved to my \user\downloads\ folder, and when I clicked Open, it opened in LibreOffice as an MS PowerPoint.
So, I don't think Win10 or Win11 have arrived at the point where it 'senses' what kind of file it's accessing. It's still dumb enough to be tricked into at least trying to open a file in a particular program based on the three-letter extension you put at the end of the filename. Fortunately...
I hope Morgan doesn't mind that I've uploaded it as a PDF here. Let me know if that's a problem.
I'm using Chrome as my browser, in Win11.
I clicked on the file Morgan uploaded, and when the "Save As" dialog box opened, I renamed the file ETF2017.ppt.
That got saved to my \user\downloads\ folder, and when I clicked Open, it opened in LibreOffice as an MS PowerPoint.
So, I don't think Win10 or Win11 have arrived at the point where it 'senses' what kind of file it's accessing. It's still dumb enough to be tricked into at least trying to open a file in a particular program based on the three-letter extension you put at the end of the filename. Fortunately...
I hope Morgan doesn't mind that I've uploaded it as a PDF here. Let me know if that's a problem.
Why should a differential pair's PSRR be other than that of any balanced design, e. g. a PP amplifier?
Anyway, even MJ isn't free of errors. I have the 3rd edition of his Valve Amplifiers book and I've detected at least two major bugs in it.
Best regards!
Anyway, even MJ isn't free of errors. I have the 3rd edition of his Valve Amplifiers book and I've detected at least two major bugs in it.
Best regards!
That makes sense, but the extra 6dB figure he then bolts onto it still confuses me. I just can't follow his line of thinking on that.