6.002
CIRCUITS AND
ELECTRONICS
Violating the Abstraction Barrier
Cite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT
OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].
6.002 Fall 2000
Lecture 25
Case 1: The Double Take
Problem
R
VO
“0” Æ “1” Vi
expected
observed
VO “1”
VO “1”
huh?
“0”
t
t
“0”
in forbidden region!
Cite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT
OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].
6.002 Fall 2000
Lecture 25
(a) DC case
R
VO
V1
Vi
Vi = 5V DC
VO = 5V DC V1 = 5V DC
very high
impedance,
like open
circuit
OK
Cite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT
OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].
6.002 Fall 2000
Lecture 25
(b)
Step
R
VO
V1
Vi
very high
impedance,
like open
circuit
5V Vi
b.1
0V
b.3
5V
t
t=0
VO
not ok!
VO = 2.5V
t=0
b.2
2T
t
5V V1
looks ok!
t=0 T
t
Cite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT
OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].
6.002 Fall 2000
Lecture 25
2.5
....
R
5
R→
Vi
characteristic
impedance
instantaneous R divider
finite propagation speed
of signals
5V
5V
5V
0
0
2T
0 T
Cite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT
OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].
6.002 Fall 2000
Lecture 25
Question: So why did our circuits work?
5V V1
rce
u
o
S
“
on”
i
t
a
n
i
Term
1. Look only at V1
0
O
M
E
D
2. Keep wires short
O
e
DEM mall wir
s
us e
3. Termination
O
DEM at the
R
add
e nd
0
t
T
5V VO
0
0
le l
l
a
r
a
P
tion
a
n
i
term
5V VO
2.5V
t
0
t
More in 6.014
Cite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT
OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].
6.002 Fall 2000
Lecture 25
Case 2: The Double Dip
Problem Æ strange spikes on supply
0
V
1
1
0
OK
driving a 50 Ω
resistor!
0
V
driving a 50 Ω
resistor!
input
Why?
Cite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT
OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].
6.002 Fall 2000
Lecture 25
Drop across inductor
Ldi
dt
VS
V
Inverter current
v inductor
VS
solution
1. short wires
2. low inductance wires
3. avoid big current swings
Cite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT
OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].
6.002 Fall 2000
Lecture 25
Case 3: The Double Team, or,
Slower may be faster!
Problem
a given chip
worked,
but was slow.
ideal
C
actual
Let’s try speeding it up by using stronger
drivers
ideal
ω
L
actual
Disaster!
Cite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT
OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].
6.002 Fall 2000
Lecture 25
Why?
DEMO
Consider
ok
C
DEMO
R1
R0
R2
dV
α
dt
dV
C
dt
crosstalk!
Cite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT
OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].
6.002 Fall 2000
Lecture 25
How does this relate to chip?
Solution
DEMO
small
Load output!
dV
dt
— put cap on outputs of chip
— jitter edges
— slew edges
Cite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT
OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].
6.002 Fall 2000
Lecture 25
Case 4: The Double Jump
Careful abstraction violation for the
better…
Recall
Vo
expect
Vi
Vo
Vi
but, observe
Vo
Vi
Cite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT
OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].
6.002 Fall 2000
Lecture 25
Case 4: The Double Jump
Careful abstraction violation for the
better…
5V
Vi
5V + 3V
5V
0V
3V
So, pullup has
stronger drive
as output rises
Cite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT
OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].
6.002 Fall 2000
Lecture 25