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Analog Building Blocks for P326 Gigatracker Front-End
ElectronicsSorin Martoiu, Univ./INFN Torino
Outline• Front-End Cell Building Blocks• CFD analysis• “CMOS” implementation
– Passive Filter– Scaling
• Dynamic Offset cancellation• Coincidence discriminator vs. zero-crossing discriminator w/
leading-edge hysteresis • Preamplifier• Single-ended to differential block• Overall performance• Additional blocks• Conclusion & Discussion
Front-End Cell Building Blocks
• PA Preamplifier• SEDB Single-ended to differential buffer• CFCF CFD filter• ZCS Zero-crossing discriminator• DD Digital driver
PA
SEDB CFDF ZCD DD
Chip Floorplan Proposal
Cell0
Cell1
CellN
Digital noise
Readout
CFD analysis
• Ideally zero time-walk• No delay-line in CMOS• LP filter instead
• σt = σnoise/(dV/dt) time-walk ~ offset/(dV/dt)
Delay
Hdelay(s) = HLP(s)
Hdiscr(s)
ZC discriminator
f
Bipolar signal
CFD analysis
• Increasing filter order performance approaches ideal delay line CFD
1 2 3 4 5
-0.3
-0.2
-0.1
0.1
0.2
1 2 3 4 5Filter order
1
1.1
1.2
1.3
1.4
1.5
epolSa.u.
“CMOS” Differential Implementation
Filter Scaling
• kT/C noise floor => high C for low noise• high peak current from input nodes• non-uniform filter – C scales up from in to out nodes, w/
RC = constant
Non-uniform scaling Uniform scaling
1,0 1,2 1,4 1,6 1,8 2,00,0
20,0µ
40,0µ
60,0µ
80,0µ
100,0µ
90,0µ
100,0µ
110,0µ
120,0µ
130,0µ
140,0µ
150,0µ
Curr
ent (A
)
K
RM
S N
ois
e (V)
1 2 3 4 510,0µ
20,0µ
30,0µ
40,0µ
50,0µ
60,0µ
70,0µ
80,0µ
90,0µ
100,0µ
80,0µ
100,0µ
120,0µ
140,0µ
160,0µ
180,0µ
200,0µ
220,0µ
Curr
ent (A
)
kc
RM
S N
ois
e (V)
Dynamic Offset Compensation
• Offset cancellation• Low-pass feedback => high-pass overall transfer
=> reduce low-frequency noise (1/f noise)
I+I
I-I
Dynamic Offset Compensation
Coincidence discriminator
• Noise produces inherent noise switching at output of ZCD
• Need parallel leading-edge discriminator to mask noise switching
• Noise switching is not eliminated
Delay
ZC discriminator
f
ZCD w/ hysteresis
• ZCD “arms” when the bipolar signal crosses a certain threshold
• Switching noise is eliminated• Additional fast block w/o offset compensation =>
may introduce some time walk
Front-End Cell Building Blocks
• PA Preamplifier• SEDB Single-ended to differential buffer• CFCF CFD filter• ZCS Zero-crossing discriminator• DD Digital driver
PA
SEDB CFDF ZCD DD
Preamplifier
• Peaking time 5ns• Gain 40mV/fC• Output noise < 1mV
@Cd=200 fF (150e- ENC)• Non-linearity < 1.5%
0,0 500,0n 1,0µ 1,5µ 2,0µ 2,5µ 3,0µ 3,5µ 4,0µ 4,5µ0,0
50,0m
100,0m
150,0m
200,0m
250,0m
300,0m
350,0m
400,0m
450,0m "vampl" Linear Fit of preamplin_vampl
Vout p
eak
(V)
Detector curent peak (A)
SED Buffer
• High drive current ~ 100uA• GBW > 500MHz• Good linearity• Good CMRR• Class AB differential opamp with CMFB and CMFF
SED Buffer
CFDF + ZCD Layout
Status
• Full channel simulations:– jitter: 100ps rms (1fC signal)– time-walk: 200ps max
Power Consumption
Block IDD (uA) P@Vdd=1.2
(uW)
PA 70 84
SEDB 250 300
ZCD 110 132
DD 70 84
Total 500 uA 600 uW
Potential problems
• Disturbances at sensitive nodes• Parasitics
– decrease bandwidth– induce non-linearity
• Input and/or output skews – affect measurement
PA
SEDB CFDF ZCD DD
Timewalk0,25
0,05
0,075
0,1
0,125
0,15
0,175
0,2
0,225
Amplitude1000 20 40 60 80
Plot 0landau distr landau distr 2
100
0
20
40
60
80
Amplitude1000 20 40 60 80
Plot 0Timewalk curve
0,25
0,05
0,075
0,1
0,125
0,15
0,175
0,2
0,225
Time error (ps)1000 20 40 60 80
Plot 0Time error distr Timewalk curve
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