Hi kgrlee,
Sorry I missed this post; I was probably in Florida on vacation.
Yes, great minds think alike. I have for quite some time planned to build and measure the various incarnations of the amplifiers in Chapter 3 for the second edition.
Glad you enjoyed Chapter 3.
My Jurassic times go back pretty far. I cut my teeth on an HK Citation 12 clone with quasi-complementary outputs
. Of course, that was after I built numerous tube amps in high school. How time flies!Cheers,
Bob
I am not surprised, because suggesting that a TIS has an all-pass characteristic is pretty indefensible.
I am not surprised, because suggesting that a TIS has an all-pass characteristic is pretty indefensible.
Let's have a miller compensated 2 stage OTA. It can be shown that the voltage transfer function has a second order denominator and a positive zero at the numerator. This positive zero comes from feedforward of miller capacitance.
If we increase the miller capacitor, we have pole splitting but after a certain value of C, the non dominant pole stops moving towards high frequencies while the dominant pole continues towards low frequencies; The positive zero decreases with C increasing and for a certain value will be lower than the non dominant pole. Then we start to have a region where the voltage gain is constant but the phase is -180° as a single negative pole followed by a single positive zero will show in a bode plot. This region way be called all pass.
Why does this kind of post sound familiar?Hi Waly
OTA is Operational Transconductance Amplifier. An OTA is like an op amp without the output current stage. It is essentially what you have with an IPS (input stage), and VAS (voltage amplifier stage). The output is very high impedance and if loaded down quickly looses it's voltage gain proportionally with the load.
The zeros require a lot more explanation. Simply put they are the -3dB attenuation points at -45 degrees on a bode plot. Perhaps someone can explain this in simple terms for you.
Cheers,
Thanks, I may know a little about poles and zeroes
. However, before properly explaining and exemplifying, all I hear is technobabble.Go to EE school and you will learn what a right-half-plane zero is. Until then, you should be politely asking questions instead of making belligerent assertions.
Cheers,
Bob
The sad thing is I did go to EE school. Used to know about bode plots, nyquist stability therorem and all that. Haven't used it for years and lost it all.
Now trying to relearn it all with respect to something I find really interesting.Thanks, but I just graduated in EE.
Rather than making belligerent comments, I would appreciate if you would stay on topic.
Thank you for your attention.
Where was the bolded expression mentionned in the very
thread you did respond to.?.
Indeed.
Ummm... I was asking if a "positive zero" is re-baptizing the thing usually known as a "RHP zero".
Good night.
Waly, Great Guru Baxandall shows clear evidence of this in the Baxandall Papers http://www.douglas-self.com/ampins/baxandall/baxandall.htm though he's using really Jurassic devices.
michaelkiwanuka said:
The VAS is indeed the PA stage that will show all-pass characteristics first. Michael, you may like to search for 'minimum phase of BJTs' on this website to remedy your ignorance of elementary analogue electronics.JPV said:
Budding Guru Waly, I apologize on behalf of Bob and us other old fogeys for not using terms with their exact meaning. 'Excess Phase' IS strictly the phase of the 'all-pass' part of a non-minimum phase transfer function.
I used to be a minimum-phase guru when I was your age but confess to have often used the term 'excess-phase' in the evil manner that Bob has
I can swear I've never been as sinful as to call RHPs what JPV does As you are closest to high academia, please excuse us forgetting what we pretended to learn in Jurassic school.
But I'm sure this discussion is nearly as fruitful as discussing VAS vs TIS with Michael
[deleted : my definitive 15 page contribution on da subject]
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Hi Bob,
If Waly has just graduated from EE then he has spent all his time studying and had little time to mature. Takes a while to shake off the high school mentality.
Cheers,
Waly, Great Guru Baxandall shows clear evidence of this in the Baxandall Papers http://www.douglas-self.com/ampins/baxandall/baxandall.htm though he's using really Jurassic devices.
The VAS is indeed the PA stage that will show all-pass characteristics first. Michael, you may like to search for 'minimum phase of BJTs' on this website to remedy your ignorance of elementary analogue electronics.
Budding Guru Waly, I apologize on behalf of Bob and us other old fogeys for not using terms with their exact meaning. 'Excess Phase' IS strictly the phase of the 'all-pass' part of a non-minimum phase transfer function.
I used to be a minimum-phase guru when I was your age but confess to have often used the term 'excess-phase' in the evil manner that Bob has
As you are closest to high academia, please excuse us forgetting what we pretended to learn in Jurassic school.
But I'm sure this discussion is nearly as fruitful as discussing VAS vs TIS with Michael
Yes, kgrlee, we old fogies do get ourselves in trouble on occasion with semantics. Sometimes I define excess phase as any phase that I wish wasn't there. Maybe like excess fat. Even in a completely minimum-phase system, I lump into the category of excess phase the sum of the phases of all of those pesky far-out poles I am too lazy to enumerate
.Life is too short, especially for us old fogies. Pass me a beer.
Cheers,
Bob