a view on electronics for the prototype of the gossip detector in 0.13um cmos technology
DESCRIPTION
A view on electronics for the prototype of the GOSSIP detector in 0.13um CMOS Technology. Vladimir Gromov Electronics Technology NIKHEF, Amsterdam, the Netherlands December the 15 th , 2004. Highlights. Main functionalities of the detector and the principal block diagram of the detector. - PowerPoint PPT PresentationTRANSCRIPT
A view on electronics for the prototype of the GOSSIP detector in 0.13um CMOS Technology.
Vladimir Gromov
Electronics TechnologyNIKHEF, Amsterdam,
the NetherlandsDecember the 15th, 2004
Highlights. • Main functionalities of the detector and the principal block
diagram of the detector.• Main specifications of the electronics.(Single electron
efficiency, time resolution, power consumption, analog-to-digital compatibility issue).
• A choice of sensitive pad-preamplifier coupling in the very front-end (calculation of the parasitic capacitances).
• Design of the preamplifier in the 0.13um CMOS technology (signal response, noise, hardness to the spread caused by the fabrication process instability).
• Design of the analog part of the read-out electronics in 0.13um CMOS.
• Performance of the detector featuring the design (efficiency, signal time-walk , overall time resolution).
• Block diagram of the DLL-based TDC. • Current-steering logic is a way to eliminate switching noise
in the mixed analog-digital design.• Conclusion.
Preamp
Shaper
Discriminator
Threshold
Latch #1
4-bit DLL 1.6ns
Latch #2
Latch #16
Preamp
Shaper
Discriminator
Latch #1
Latch #2
Latch #16
to Read-0ut Clock 40MHz
Integral circuit in 0.13um CMOS technology
Cathode (drift) plane
Ingrid
Cluster2 Cluster1
Cluster3
Track of the particle
Drift distance
The principal block diagram of the detector.
Z Y
X
Main functionalities of the device:
1) The pixel structure with a fine pitch (30um …50um) can provide accurate information on X-Y coordinate of each cluster on the track. Thus the projection of the track is seen.2) With having measured the drift time of each cluster the angle between the track and X-Y plane can be found in order to depict a 3D picture.
Design objectives on the read-out electronics:
a) the fact that the pixel has been hit needs to be detected with high efficiency and low faulty. The hit should be correctly related to a proper bunch-crossing.b) drift time is to be measured as a latency of the hit arrival time in respect to the bunch-crossing signal accurate enough to determine Z - coordinate of the cluster.
Design objective
the desirable vs the possible
Main specifications of the electronics:
1) Single electron efficiency (input referred electronic noise).The fluctuations in the number of electrons in a single-electron avalanche is given by:
P(n) = 1/M * exp(-n/M) , where M is a gas gain factor.
With the input referred threshold at the level of 500e inefficiency will be 20% (gas gain M=2000)10% (gas gain M=4000)6% (gas gain M=8000) .
The threshold of 448e corresponds to ENC = 90e RMS
20%
10%
0 500 1000 1500 2000 2500 3000 3500 4000 4500 50000
0.2
0.4
0.6
0.8
11
0
P n 2000( )
P n 4000( )
P n 8000( )
n
50000 n n n 448
Gain=4000
Gain=2000
Gain=8000
Inefficiency
Threshold, electrons448e
2) Time resolution.Both the time resolution of the TDC and the time-walk in the discriminator are
independent contributors to the overall time resolution (σΣ ) of the electronics: σΣ = √ (σ2
TDS + σ2Time walk) ,
where σTDS = ∆t/√12 , ∆t – minimum bin size of the TDS
σTime walk is dispersion, related to the time-walk in the discriminator
For a 4-bit DLL-based TDC ∆t = 25ns/16 = 1.6ns it yields σTDS = 0.46ns .The electron drift velocity in the gas is about 20ns/mm therefore the TDC contribution to
the overall spatial resolution will be σspatial
TDS = 23um.
Under these conditions time walk in the discriminator become the main contributor.
Time-walk. Where does it come from?
Signal at the output of discriminator (Sout(t)) is a convolution integral of input current i(t) and pulse response function (H(t)) of the electronics.
0 20 40 60 8020
15
10
5
00
19.355
S t 1 10( ) 448
13
f t 1 10( ) 250
5
900 t
Low threshold
High threshold
Time, ns
Sout(t)Signals at the
input of discriminator,
arbitrary unit
Range of time-walk for the fast shaped signal
Range of time-walk for the slow shaped signal
A fast shaped signal
A slow shaped signal
Sout t( )0
tH ( ) i t ( ) d
i(t) - input current :Ion current occurs in the Micromegas-pad gap in the period
∆tion= (∆L)2/μ U ≈ 30ns, where ∆L ≈ 50um is the Micromegas-pad distance
U ≈ 400V is Micromegas-pad voltageμ= 1.72cm2V-1 sec-1 is mobility of ions in Argon
Single-electron current in the detector
20 0 20 400.15
0.1
0.05
0
s t( )
t
20 0 20 401.5
1
0.5
0
S t1( )
t1
Integral of current induced by a single electron.
time,ns time,ns
i(t)
electron component
ion component
10% is electron contribution to
theoverall charge 90% is ion
contribution to theoverall charge
H(t) - shaping function (δ-pulse response)
Let us take shaping function of the electronics as follows F(p)=1/[(p 1 + 1) (p 2+1)]. It demonstrates pulse response f (t, 1 2 )
f t 1 2( ) 11 2( )
exp t1
exp t2
0 10 20 30 40 50 600
0.02
0.04
0.06
0.08
f t 1 10( )
f t 8 10( )
ttime,ns
Pulse response of the electronics (τ1=1ns, τ2=10ns)
Pulse response of the electronics (τ1=8ns, τ2=10ns)
Distribution of the threshold-crossing time. Monte-Carlo simulations.
0 2 4 6 8 100
200
400
600
Integrals of the distributions.
0 2 4 6 8 100
5000
1 104
EntriesGain=2000, Thr = 448e, τ1=1ns, τ2=10ns
Gain=2000, Thr = 448e, τ1=8ns, τ2=10ns
time,ns
time,ns
Entries Gain=2000, Thr = 448e, τ1=1ns, τ2=10ns
Gain=2000, Thr = 448e, τ1=8ns, τ2=10nsinefficiency=20%
!!! Fast shaping enables us to get much better time resolution at a given gas gain (threshold).!!! Fast shaping enables us to get much better time resolution at a given gas gain (threshold).
3) Power consumption.
Number of channels per wafer = π D2/(4 pitch2) = 3.14 * 106
with power consumption 10W/wafer (possible to cool it down by gas flow) !!! Power consumption per channel = 3.2uW !!! Power consumption per channel = 3.2uW
4) Switching noise.
In a mixed-mode design switching noise coming from digital part of the circuit back to high sensitive analog front-end is a very important issue. The most most common way to eliminate switching noise is using current-steering logic. Although it reduces speed and increase static power consumption.
D=10cm
pitch =50um
Preamp Preamp
Ingrid
Preamp
i(t)
C1
C2C2 C3 C0 ~ 20pF
R0
U1=-300V…-400V
C4
R4
-800V
Cathode (drift) plane
R1
The very front-end. DC or AC coupling to the Preamp.
The very front-end. DC or AC coupling to the Preamp.
Safety DC-coupling AC-coupling
C0
C3 4*C2
Zin≈0Zin/4≈0
Qd=U1*C0
Discharge trajectory
C0
C34*C2
C1
Zin≈0
Zin/4≈0
R1
Qd=U1*C5
Discharge trajectory
C5=C0*C1/(C0+C1) ≈ C1 C1 C0
i(t)
C0
C3 4*C2Zin≈0
Zin/4≈0
i1(t) iin(t)
i(t)
C0
C34*C2
C1
Zin≈0Zin/4≈0
i1(t) iin(t)
R1
In order to collect much of the charge iin(t) ≈ i(t) the following condition must be met C1 C3+4*C2.For better safety C1 0. Therefore values of the parasitic capacitors C3,C4 are important to know.
Signal collection DC-coupling AC-coupling
C R d( ) 2 3.14 0
0
dz
0
1rr z
z2 r2 R2
32
d d
0 5 10 6 1 10 5 1.5 10 5 2 10 5 2.5 10 50
0.5
1
1.5
2
2.5
C R 25 10 6
C R 50 10 6
C R 75 10 6
R
C=1.8fF whenR=25um, d=50um
Pad-to-Micromegas grid capacitance calculations.
R - is a radius of the pad. The pad is a circle. d - is pad-to-Micromegas distance.0 - is vacuum dielectric constant.
DIdeal boundless plane
Ideal uniformly charged disk
R
0 5 10 6 1 10 5 1.5 10 5 2 10 5 2.5 10 5 3 10 50.1
0.2
0.3
0.4
0.5
0.6
0.645
0.111
C1 b( )
3.5 10 55 10 6 b
C=0.62fF whenb=30um, a=20um,pitch=50um
Conclusion: C3+4*C2 = 1.8fF +4*0.62fF = 4.32fFConclusion: C3+4*C2 = 1.8fF +4*0.62fF = 4.32fFIn order to collect much of the charge iIn order to collect much of the charge iinin(t) ≈ i(t) the following condition must be met C1 4fF(t) ≈ i(t) the following condition must be met C1 4fF
C1 b( ) 4 3.14 0 r
2 10 10
a b( )2
z
0.5
0.5xz
z2 x2 b2
32
d d
a
b
b
Ideal uniformly charged square padIdeal uniformly charged square pad
b - is length of the pad. The pad is a squire . 50um is a pitch[50um-b] - is a pad-to-pad distance.0 - is vacuum dielectric constant.r=4 - is relative permittivity of the dielectric.
Pad-to-Pad capacitance calculations.
Input Output
T249Id= -1uGm = 2.4uGds = 26nVgs= -963mVVds=-957mV (Vds_sat=-658mV)Cgg= 57.7fFCdd+Cjd=0.451fF+0.150fF=0.6f
T245Id= 1uGm = 23.2uGds = 0.7uVgs= 234mVVds=243mV (Vds_sat=45mV)Cgg= 2.6fFCdg=0.8fFCdd+Cjd=0.8fF+0.7fF=1.5f
Schematic of the Preamplifier. Main specifications.Technology: 0.13um CMOS.Power supply voltage:1.2VPower consumption: 1uA * 1.2V = 1.2uW.Charge sensitivity (real detector current pulse): 33mv/448e. Shaping function: rise time is 6ns, decay time is 100ns.Output noise (RMS): 4.3mVEquivalent input noise (RMS): (4.3mV/33mV)*448e = 58e
Cdg=0.8fF100MΩ
Idc=6nA
Input signal is a current δ-pulse
Output signal as a response to the δ-pulse
Input signal is a real current pulse
Output signal as a response to the real current pulse
Spectral density of the squire of the noise output
voltage|V2
n(jw)|
18.5uV2
4.3mV
The preamplifier. Simulation results.
Input OutputIdc
The preamplifier. Monte-Carlo analysis in Affirma Spectre.
Channel-to-channel variations of the bias current Inom=1uAσ=5%
Channel-to-channel variations of output voltage Unom=247mVσ=6.5%
Channel-to-channel variations of gain (charge sensitivity) GAINnom=33mV/448eσ=8.7%
Schematic of the Preamp + Shaper + Discriminator. Main specifications.Technology: 0.13um CMOS.Power supply voltage:1.2VPower consumption: 1.6uA * 1.2V = 1.92uW (3.3*106 channels per wafer or 6.3W per wafer) .Charge sensitivity (real detector current pulse at the shaper output): 254mv/448e. Shaping function: rise time is 23ns, decay time is 100ns.Output noise (RMS): 37mVEquivalent input noise (RMS) at the shaper’s output: (37mV/254mV)*448e = 65e
Input
Output240nA
100nA
300nA1000nA
Input current
Preamp output
Shaper output + threshold
Output of the first stage of the discriminator
Output of the discriminator
Channel-to-channel gain variations at the output of the shaper GAINnom=254mV/448eσ=10%
Channel-to-channel variations of the voltage at the output of the shaper σ = 18mV Uthr=190mV.
Preamplifier + Shaper + Discriminator. Simulation results and Monte-Carlo analysis in Affirma Spectre.
Walk-time as a function of the signal amplitude (THR=448e)
0.8*448e
1*448e1.5*448e
2*448e3*448e
5*448e
12*448e
20*448e
50*448e
Preamplifier + Shaper + Discriminator. Statistical analysis.
0 5000 1 104 1.5 104 2 104 2.5 104 3 1040
10
20
30
34
0
P n 2000( ) 32
P n 4000( ) 32
P n 8000( ) 32
n
Twalk jt 1
Tw n( )
300000 n n n 448 Twalk jt 0 448 n
Time-walk vs pulse height distribution
Signal, electronsTHR=448e
Gain=8000
Gain=4000
Gain=2000
Time-walk curve
0 5 10 15 20 25 30 35 400
1000
2000
3000
40004000
0
DISTRT2000 nt
DISTRT4000 nt
DISTRT8000 nt
1
nt
nt1
DISTRT2000 nt125
=
1
nt
nt1
DISTRT4000 nt125
=
1
nt
nt1
DISTRT8000 nt125
=
39.90 inttnttime,ns
Entriesefficiency=100%
Time resolution (time distribution of the threshold crossing events). Statistics is 10000.
Gain = 8000
Gain = 4000
Gain = 2000
Preamplifier + Shaper + Discriminator. Statistical analysis. Time resolution
!!! It is feasible to reach time resolution of order of σ=2ns (100um) with a realistic gas gain.!!! It is feasible to reach time resolution of order of σ=2ns (100um) with a realistic gas gain.
Phase detector
Clk40MHz
Delay chain. DLL
#1 #2 #3 #4 #16
Block diagram of the DLL.
Vdd=1.2V
bias1
bias2
bias3
In +
In -Out+
Out-
An inverter in low-voltage current-steering logic.
±200mV
Conclusion..The TimePix detector is going to be a powerful tool for future experiments.. Definition of the topology and specifications of the detector is in progress on the basis of
the potentialities of the modern deep sub-micron CMOS technology . The following specification have been found feasible so far:
Gas gain: 2000-8000. Single electron efficiency: 80%-94%. Input referred threshold: 500e. Time resolution: σ = 2ns corresponding to spatial resolution σ = 100um. Power dissipation: 3.2uW/channel (10W/wafer). AC coupling to the preamplifier looks preferable from safety point of view. Not
much of the signal will be lost if the coupling capacitor is as tiny as 30fF…40fF. .First trial to design an analog circuit in the 0.13um CMOS technology capable to meet the
specification has shown a promising result.. DLL-based TDC structure is a possible candidate for time-to-digital conversion block. . More efforts needs to be made to design switching noise free logic cells.