04/02/02EECS 3121 Lecture 23: DRAM + Driving large capacitances EECS 312 Reading: 10.3.3, 8.2.3, 8.5...
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Transcript of 04/02/02EECS 3121 Lecture 23: DRAM + Driving large capacitances EECS 312 Reading: 10.3.3, 8.2.3, 8.5...
04/02/02 EECS 312 1
Lecture 23: DRAM + Driving large capacitances
EECS 312
Reading: 10.3.3, 8.2.3, 8.5 (text)
04/02/02 EECS 312 2
Lecture Overview
• Midterm 2 review
• Finish discussion of memories
• Chip packaging overview
• Driving large loads
04/02/02 EECS 312 3
Midterm 2
04/02/02 EECS 312 4
Packaging
Requirements
• Electrical: Low parasitics
• Mechanical: Reliable and Robust
• Thermal: Efficient Heat Removal
• Economical: Cheap
04/02/02 EECS 312 5
Bonding Techniques
Lead Frame
Substrate
Die
Pad
Wire Bonding
04/02/02 EECS 312 6
Flip-Chip Bonding
Solder bumps
Substrate
Die
Interconnect
layers
04/02/02 EECS 312 7
Package Types
04/02/02 EECS 312 8
Package Parameters
04/02/02 EECS 312 9
Driving Large Capacitances
VDD
Vin Vout
CL
tpHL = CL Vswing/2
Iav
Transistor
Sizing
04/02/02 EECS 312 10
Using Cascaded Buffers
C2C1
Ci
CL
1 u u2 uN-1
In Out
uopt = eThis ignores self-loading (junction capacitance of driving stage): derivation on page 450 of text
X = CL/Cin
u = tapering factor
04/02/02 EECS 312 11
tp as a function of u and x
1.0 3.0 5.0 7.0u
0.0
20.0
40.0
60.0
u/l
n(u
)
x=10
x=100
x=1000
x=10,000
04/02/02 EECS 312 12
Impact of Cascading Buffers
04/02/02 EECS 312 13
Output Driver Design
04/02/02 EECS 312 14
How to Design Large Transistors
G(ate)
S(ource)
D(rain)
Multiple
Contacts
S
S
G
D
(a) small transistors in parallel(b) circular transistors
We don’t want a long poly run – resistive and large parasitics
Place multiple narrower devices in parallel (with same gate signal)
04/02/02 EECS 312 15
Tristate Buffers
In
VDD
En
EnOut
VDD
Out
In
En
En
Useful for signals with multiple drivers
2nd implementation is better in some cases b/c no series connected devices in output stage
04/02/02 EECS 312 16
Lecture Summary
• Chips must be put in a package to interface with other devices
• Sending signals off-chip requires a lot of driving capability
• Driving large loads is best done using cascaded buffers with tapering factor of e