T
Tim Wescott
- Jan 1, 1970
- 0
PaulCsouls said:
You get matched transistors -- there used to be some RCA chips
available; if they aren't still out there Zetex has some matched pairs
they sell for current mirrors.
You get matched transistors -- there used to be some RCA chips
available; if they aren't still out there Zetex has some matched pairs
they sell for current mirrors.
W
Winfield Hill
- Jan 1, 1970
- 0
Ken Smith wrote...
If you leave that out it won't operate to the negative rail,
which is its most important feature. The LM324 output stage
is severely in need of improvement, but it'll still need to
go down to 0V. ...
If you leave that out it won't operate to the negative rail,
which is its most important feature. The LM324 output stage
is severely in need of improvement, but it'll still need to
go down to 0V. ...
K
Ken Smith
- Jan 1, 1970
- 0
In that case you really-really need glasses.
Go back and read my post. I was explaining why it is bad to simple answer
the poster's question with a complete solution. There is no case in which
it is a good thing to do in the situation as it is.
K
Ken Smith
- Jan 1, 1970
- 0
No, some designs of op-amps require matched components. Other designs do
not. They only need the parts to be within the normal process span.
You can trim the offset voltage out out with a trimmer. The offset
bias current can often be ignored. The output stage bias point can be
made value independant enough if you are willing to trade off gain per
device and swing. Lots of op-amps got built before ICs.
K
Ken Smith
- Jan 1, 1970
- 0
If the OP is just trying to get a starting point, operation down to the
negative rail can be set aside. Yes the output stage sucks but it is
simple.
R
Rich Grise
- Jan 1, 1970
- 0
The teacher, maybe?
How the hell are we supposed to know? We weren't sitting in on
the lectures you skipped any more than you apparently were. And
we don't have your textbook.
The ones that the teacher is going to grade your score on.
You're welcome.
Rich
P
PaulCsouls
- Jan 1, 1970
- 0
I stand corrected.
Paul C
Paul C
J
Jim Thompson
- Jan 1, 1970
- 0
See "MC1530-TeachingExercise.pdf" on the SED/Schematics page of my
website.
You can even build it with 2N3904's, EXCEPT: change R10 from 3.4K to
3.3K and add 100 ohm resistors in each of the emitter paths for Q9 and
Q10 (since discrete parts won't match accurately enough for raw
current mirror use).
...Jim Thompson
W
Winfield Hill
- Jan 1, 1970
- 0
Ken Smith wrote...
Simple, but pedagogically best as an example of how not to do it.
Simple, but pedagogically best as an example of how not to do it.
D
Daniel Haude
- Jan 1, 1970
- 0
On Sun, 07 Nov 2004 16:58:31 -0700,
Nice! What's a quadrille pad? What's Lubyrith?
--Daniel
in Msg. said:
Nice! What's a quadrille pad? What's Lubyrith?
--Daniel
P
Paul Burridge
- Jan 1, 1970
- 0
It can't be *that* bad. In that poll of "classic chips" we had last
year, the 324 was one of the most popular, ISTR.
F
Fred Bloggs
- Jan 1, 1970
- 0
Winfield said:
Non-sense, it's a great little opamp.
J
Jim Thompson
- Jan 1, 1970
- 0
A "quadrille pad" is just a pad of paper with a blue grid on it. I
used 10-to-the-inch paper.
Ouch! Typo! "Lubyrith" should be "Rubylith", a two-layer material,
one layer red, one layer clear.
You cut the red layer away with a sharp knife or special-made cutter,
leaving clear areas for photographic exposure. I believe the material
was originally used for PCBs.
Now-a-days it's all done in software and a GDSII data stream defines
the images.
I designed the MC1530 when I was 23 years old.
...Jim Thompson
J
Jim Thompson
- Jan 1, 1970
- 0
[snip]
Typo is now corrected.
...Jim Thompson
J
Jim Thompson
- Jan 1, 1970
- 0
On a bipolar process you don't have many choices. The vertical PNP
plus current sink _did_ get you _almost_ to negative rail ;-)
The biggest problem was brand variability... Motorola's copy had such
severe cross-over distortion as to make the part unusable for active
filters... which is why I put the Motorola LM324 on the GenRad
(OmniComp) do-not-purchase list.
...Jim Thompson
W
Winfield Hill
- Jan 1, 1970
- 0
Jim Thompson wrote...
My complaint is not with the pulldown circuitry.
To my knowledge, this problem was equally bad with '324 parts from
all the manufacturers. I suppose they chose *zero* class-AB current
to help insure the 50uA pulldown could reach closer to the negative
rail, but it's a great example of how *not* to do it.
My complaint is not with the pulldown circuitry.
To my knowledge, this problem was equally bad with '324 parts from
all the manufacturers. I suppose they chose *zero* class-AB current
to help insure the 50uA pulldown could reach closer to the negative
rail, but it's a great example of how *not* to do it.
J
Jim Thompson
- Jan 1, 1970
- 0
Not so. TI and National parts were demonstrably better than Motorola
parts. (At least in mid to late '70's when I was using them like
popcorn.)
I ultimately eliminated the problem with a pull-down resistor from
output to minus supply, keeping the output class-A.
While I never dissected an LM324, I suspect that some versions derived
the 50uA from mirroring via a replica of Q12 (National data sheet
reference designators).
Might be an interesting exercise to trace one out under a microscope:
If you look at the published schematic, the output stage cannot
function properly, it has a major problem... can you tell us what it
is?
How would _you_ do it, Win ?
...Jim Thompson
K
Ken Smith
- Jan 1, 1970
- 0
The output section has about 3 diodes worth of crossover distortion and
the compensation does not enclose that distortion so at high frequencies,
it appears in the output. It also makes the output impedance rise quite a
bit for increasing frequencies and vary a lot with load current. This can
lead to trouble when you use them to drive a transistor buffer.
J
Jim Thompson
- Jan 1, 1970
- 0
The "simplified schematic" is flawed... it can't be as-drawn... there
is a fundamental error. I tried to tease Win into _stepping_in_it_,
but he won't take the bait ;-)
And what's this statement, "...compensation does not enclose that
distortion..."?
...Jim Thompson
W
Winfield Hill
- Jan 1, 1970
- 0
Jim Thompson wrote...
Some of us have work to do! I assume you're referring to Q7's collector-
base diode in parallel with Q13's base-emitter (NSC diagram, Q12 and Q11
for Motorola), during pulldown. We don't know the relative I_s values...
Do you have access to a proper full schematic?
He's referring to the compensation cap connected to the base of a pullup
output transistor, rather than to the output, forcing a slew time delay
when traversing from pullup to pulldown, and back. No doubt the chosen
cap connection is more stable, and perhaps protects the cap from static
discharge damage too. But it exacerbates the crossover distortion.
Some of us have work to do! I assume you're referring to Q7's collector-
base diode in parallel with Q13's base-emitter (NSC diagram, Q12 and Q11
for Motorola), during pulldown. We don't know the relative I_s values...
Do you have access to a proper full schematic?
He's referring to the compensation cap connected to the base of a pullup
output transistor, rather than to the output, forcing a slew time delay
when traversing from pullup to pulldown, and back. No doubt the chosen
cap connection is more stable, and perhaps protects the cap from static
discharge damage too. But it exacerbates the crossover distortion.
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