Short Pulse Reading Concept An initial voltage (V+,V-) can be setup by the sensing
stage for the S.A. After the S.A is enabled, all initial points in the blue
region above MSL will be latched as “1”, all those in the red region below MSL will be latched as “0”.
However, MSL can vary widely due to mismatch, process and temperature variation, so any initial point in the MSLregion may result in reading error.
The key of short pulse reading is to effectively setup initial voltage points accordingly for the S.A, which should be as far way from the MSL region as possible.
The distance from initial voltage to the boundary of MSLregion is defined as noise margin.
1
Simulated MSL Variation
Direct sensing
Need to add capacitance to the input nodes of dynamic latch.
2
Visualization of Sensing Stage
TMR v.s. RM
Rp = 2.9kΩ, VDD=1V Increasing TMR can increase NM very effectively. For
practical TMR the NM is very small.
30 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
V+
V-
TMR= 50TMR= 75
TMR=100
TMR=150TMR=200
TMR=300
TMR=400
TMR=500TMR=600
TMR=700
TMR=800TMR=900
0 100 200 300 400 500 600 700 800 900-200
-150
-100
-50
0
50
100
150
TMR(%)
Noi
se M
argi
n (m
V)
Vp
Vap
Vap
Vp
Rpv.s. RM
TMR = 110%, VDD=1V
Only increasing Rp won’t help NM, since both Ip and Iap are affected.
40 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
V+
V-
Rp=0.5k
Rp= 1k
Rp=1.5k
Rp= 2k
Rp=2.5k
Rp= 3k
Rp=3.5k
Rp= 4k
Rp=4.5k
Rp= 5k
Rp= 6k
Rp= 7k
Rp= 8k
Rp= 9k
Rp= 10k
0 1 2 3 4 5 6 7 8 9 10-50
-40
-30
-20
-10
0
10
20
30
40
Rp(k)
Noi
se M
argi
n (m
V)
Sizing v.s. RM
Rp = 2.9kΩ, TMR = 110%, VDD=1V Purely increase the read current (e.g. by sizing the mirror
transistor), won’t help RM.
50 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
V+
V-
W= 5umW= 7.5um
W= 10um
W=12.5um
W= 15um
W=17.5umW= 20um
W=22.5um
W= 25um
W=27.5umW= 30um
5 10 15 20 25 30-40
-30
-20
-10
0
10
20
30
40
W(m)
Noi
se M
argi
n (m
V)
Differential Sensing
Need to minimize the capacitance to the input nodes of dynamic latch.– The longer the sensing state is, the better.
6
Visualization of Sensing Stage
Reverse Sensing
Need to minimize the capacitance to the input nodes of dynamic latch.– The longer the sensing state is, the better.
7
Visualization of Sensing Stage
Differential Sensing NM
Need at least 2.5 ns to have worst case NM>0
8
1 2 3 4 5 6 7 8 9 10-250
-200
-150
-100
-50
0
50
100
150
200
250
Sensing Time (ns)
Noi
se M
argi
n (m
V)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
V+
V-
1ns
2ns 3ns
4ns
5ns
6ns
7ns
8ns 9ns
10ns
Vap Vp
Vap
Vp
Reverse Sensing NM
NM is not symmetric, need to be optimized Need at least 2 ns to have worst case NM>0
9
1 2 3 4 5 6 7 8 9 10-500
-400
-300
-200
-100
0
100
200
300
400
500
Sensing Time (ns)
Noi
se M
argi
n (m
V)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
V+
V-
1ns
2ns 3ns
4ns
5ns
6ns
7ns
8ns 9ns
10nsVap
Vp
Vp
Vap
DS v.s. RS
10
1 2 3 4 5 6 7 8 9 10-150
-100
-50
0
50
100
150
200
250
300
Sensing Time (ns)
Noi
se M
argi
n (m
V)
NM of Vp (DS)
NM of Vap (DS)
NM of Vp (RS)
NM of Vap (RS)
1 2 3 4 5 6 7 8 9 10-150
-100
-50
0
50
100
150
200
Sensing Time (ns)
Noi
se M
argi
n (m
V)
NM of Vp (DS)
NM of Vap (DS)
NM of Vp (RS)
NM of Vap (RS)
Differential Sensing Improves NM
11
Direct Sensing Differential Sensing
Visualization of Sensing Stage Simulated NM for the same setting
Current Work
Optimizing and getting data from differential sensing.
Will try dual differential sensing, which should work even better.
12