1. SAS-3 Transmitter Training Review
Harvey Newman
April 14, 2011
T10/11-164r2

2. SAS proposal for control register proposed in 10-025r0
Index
Name
Values 15
Reset
1 = Reset coefficients to the no equalization state (e.g. ci=0 for i ≠ D)
0 = Normal operation
14:6
Reserved
Write as zero, ignore on read
5:4
Coefficient (+1) update request
5 4
1 1 = Reserved
1 0 = Decrement
0 1 = Increment
0 0 = Hold
3:2
Coefficient (0) update request
Encoding per coefficient (+1) update request
1:0
Coefficient (-1) update request
T10/11-164r2

3. Revised Proposal for SAS Control Register 11-044r0
Index
Name
Values
15:14
Coefficient settings
11b = Reserved
10b = Default coefficients (set by manufacturer)
01b = Set Tx to a specified operating condition to be determined by the phy committee (Reference)
(Not persistent across reset, reference Tx mode for characterization)
00b = Normal operation (up to Tx to determine, may use default or last know value)
13:6
Reserved
Write as zero, ignore on read
5:4
Coefficient (+1) update request
5 4
1 1 = Reserved
1 0 = Decrement
0 1 = Increment
0 0 = Hold
3:2
Coefficient (0) update request
Encoding per coefficient (+1) update request
1:0
Coefficient (-1) update request
T10/11-164r2

4. Revised Proposal for SAS Control Register 11-036r2
Index
Name
Values
15:13
Pattern Type
All others = Reserved
000b = Normal operation (up to Tx to determine, may use default or last know value) 12
Reserved
Write as zero, ignore on read
11-10
Coefficient Settings
11b = Reserved
10b = Default coefficients (set by manufacturer)
01b = Set Tx to a specified operating condition to be determined by the phy committee (Reference)
00b = Normal operation (up to Tx to determine, may use default or last know value)
9:6
5:4
Coefficient (+1) update request
5 4
1 1 = Reserved
1 0 = Decrement
0 1 = Increment
0 0 = Hold
3:2
Coefficient (0) update request
Encoding per coefficient (+1) update request
1:0
Coefficient (-1) update request
T10/11-164r2

5. Coefficient Update Proposed in 10-025r0
Coefficient Update Proposed in r0. Dashed Line Represents Waveform Before Update.
V3(k)
V1(k-1)
V1(k)
V3(k)
V1(k-1)
V3(k-1)
V3(k-1)
V1(k-1)
V2(k)
V2(k-1)
V2(k)
V1(k)
V2(k-1)
V1(k)
V2(k-1)
V3(k-1)
V1(k-1)
V2(k-1)
V3(k)
V2(k)
V3(k)
V1(k)
V3(k-1)
V2(k)
C(-1) Increment
C(1) Increment
C(1) Decrement
C(-1) Decrement
V1(k)
V3(k)
V1(k-1)
V3(k-1)
V2(k)
V2(k-1)
V1(k-1)
V2(k-1)
V3(k-1)
V1(k)
V2(k)
V3(k)
C(0) Increment
C(0) Decrement
Cpost
Cctr
Cpre
T10/11-164r2

6. Maxim Commands Summary 11-049r3
All green commands are 2dV
T10/11-164r2

7. Maxim Proposed Commands 11-049r3
All green commands are 1dV.
They should be twice as large because two steps are being applied.
T10/11-164r2

8. Eleven commands with adjusted numbers to match original proposal.
T10/11-164r2

9. What do we what to specify?
Maximum amplitude at the Transmitter connector
1200mVppd
This provides a maximum Voltage limit for future generations.
Minimum amount of equalization available from the transmitter
Receivers will not have the ability to fully equalize the worst case channel without some help from the transmitter.
Monotinicity for transmitter adjustment.
In order to allow the control loop in the receiver to converge to an optimal equalizer setting when it tells the transmitter to increase equalization, the transmitter shall not decrease equalization.
This is why the transmitter minimum step size is a value greater than zero.
Maximum stress caused by a compliant TxRxConnection
The amount of total system equalization has to be specified greater than the worst case compliant TxRxConnection.
Some of the equalization will be at the transmitter and some at the receiver.
Starting point for equalization search.
T10/11-164r2

10. What do we not want to specify?
Implementation
We want to allow transmitters to be either voltage mode or current mode drivers.
We want to allow receivers to apply a variety of different types of equalization and even combinations of multiple types.
Linear (boost high frequency, works best for smooth channels)
DFE (works best for “bumpy” channels and does not amplify crosstalk)
Algorithms
There will be multiple different ways to search for an optimal system equalization
Parameters within the control of a single deliverable
Signal wave shape at the die is not of interest for compliance when the package and remaining interconnect out to the SAS compliance point is part of the transmitter device.
Preset values based on worst case channel analysis
The worst case channels represent a small percentage of the overall implementations.
T10/11-164r2

11. This implies adjusting Cpre 5 times has no change in the Cpost
This implies adjusting Cpre 5 times has no change in the Cpost. See next slide.
T10/11-164r2

12. Adjusting Either Pre or Post Interacts with the Other
Adjusting Either Pre or Post Interacts with the Other. Note: 10mV steps are the smallest allowed when two steps are taken together.
Allowing Cpre or Cpost adjustment without tying it to Cctr provides twice the resolution for our equalization without increasing the number of dimensions in the search.
T10/11-164r2

13. Why provide an example with 100mV VMA?
The maximum amplitude is 1200mV, this leads to an operating voltage around 1000mV
The worst case channels we have been looking at have in the order of 20dB signal attenuation at Nyquist.
This reduces the high frequency components from 1000mV to 100mV
Note 20dB is a ratio of 1/10th
To equalize the system we want to have the high frequency and low frequency signal energy nearly the same.
Receivers sample signals on the order of 100mV after signal conditioning.
If crosstalk is significant then reducing transmitted signal amplitude is more beneficial than attenuating the signal inside the receiver.
We need to allow the receiver to adjust for optimal system performance.
T10/11-164r2

14. Insertion loss Vs. NEXT from 10-025r0
T10/10-025r0

15. Amplitude Changes Equalization
Once there is equalization an amplitude change causes a change in the equalization applied.
If we equalize then adjust C0 you have changed the amount of equalization.
After the change you want to only adjust equalization.
We would like to minimize the interaction between adjustments.
Constant swing commands cause an interaction between Pre and Post
T10/11-164r2

16. Constant Swing Adjustments Following an Amplitude Change
T10/11-164r2

17. T10/11-164r2

18. Maxim proposal for compliance point from 11-049r3
T10/11-164r2

19. Connector Compliance Point Preferred Over Virtual Point
Virtual compliance points complicate measurement and interoperability
Limits maximum signal swing before a known amount of loss
T10/11-164r2

20. LSI Proprietary