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~ ~ Ishy0 shy

~ ~ -1

lt1 1

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LALRT 97middot04 Occcmhcr 11lt)7

NOV 2 1888

A discriminator and shaper circuit realized in CMOS technology for BABAR

J Ardelean RL Chase A Hrisoho S Sen K Truong G Wormser

Laboratoire de LA(cilerateur lineaire IN2P3-CNRS ~t Universiti de Paris-Sud BP 34 Fmiddot91898 Ona) Ccdex

Preunted bl A Hrisoho at the 7 Pisa Meetingon Advanted Detectors

LeI Biotlnla Ifola dElba Uvomo (ltllly) May 25-31 1997

~ ~

UER Institut National de de Physique Nucleaire

Universite ParismiddotSud et de Physique des Particules

BP34 - Batimcnr 20() - 91898 ORSAY CEDEX

LALIRT 97-04 December 19gt7

A discriminator and shaper circuit realized In CMOS technology for BABAR

J Ardelean R L Chase A Hrisoho S Sen K Truong G Worms(r

Labomtoirr dr IA r-rfMralfllr Lineai1f JN2 PS- (N RS et lfniversitf Paris Sud F-91405 OTsoy FmnCf

J

Presented by A Hrisoho at the 7th Pisa Meeting on Advanced Detectors

La Biodola Isola dElba Livorno (Italy) May 25-31 1997

Abstract

An analog chip is designed to receive from a PM through a son coaxial cable signals rising in 3ns falling in Sns and to provide

digita signals for timing purposes multiplexed analog output proportional to the input for spectral measurements

There are 8 channels per chip with a common gain adjustment for the preamplifier and individual control for the offset and threshold setti ng TI1( discriminator senshysitivity is 2mV The dynamic range is from 2mV to IOOmV The noise equivalent at the input is ~ lOOlV The RMS time dispersion is less than SOOps for 3mV th reshold

The shaping amplifier is of bipolar s hape with Sans peaking time and 2 sV mean output voltage The crosstalk between cliannels is less than 2

1 Introduction

T he e lectroni cs chain is designed to record single photoelectron signals from P MTs with maximum efficiency and to note their arrival time with better than Ins precision which is necessary to reject background hits at the patshytern recogn ition level The desired time resolution is determined by the PMT time resolution of 18ns The e lectronic chain should not degrade this any further Since even background hits are also single photoelectron events thp

P MT amplitude does not carry any useful information for data analysis and is therefore registered on a multiplexed basis only for monitoring purposes As a conseq ue nce the disc riminator must acbiev its timing reso lution oVtr thp

2

3

whole PMT single photoelectron amplitude spectrum which covers the range from 2m V to 60mV at normal operating PMT high voltage

Circuit description

The circuit is designed to receive single photoelectron signals from a photoshymultiplier There are 8 channels on a CMOS technology ASIC with a digital output for timing and a multiplexed linear output for PMT gain monitoring A simplified diagram of the circuit is given on Fig 1

(CAIN CONTPOL

I N + Ol e

I ____bull ore OUT

IN-

p j

C I

IrN U

Tl = PI C I fa = K POI~~ bull CDI~~ T3 = K P3 bull C3

Fig 1 A simplified diagram of one channel

Each channel is composed of an amplifier with gain adjustment by a comshymon digital control for the 8 channels The amplifier differential output is followed by two buffers driving the discriminator circuit and the shaping cirshycuit respectively The discriminator is driven differentially whereas the shaper circuit is single-ended This has been done in order to minimize cross-talk to the neighboring channels in the fast discriminator part of the circuit and to compensate for temperature dependent threshold drifts which would affect the timing precision

The amplifier

It is a differential pair cascode in which the differential pair current is defined by the current source 11 and the cascode current is the difference [2 - Id2 of

2

4

the current sourCfS [2 aIld II respectively (Fig 2) The gClin of the amplifier is gi ven by

~ II gmi 1nmiddot (J)

gm2

Where gmi is the transconductance of the diffprential pair NMOS gm2 is the transconductance of the cascode load NMOS

j Il

-1

OUT u

GM2 -I

Fig 2 Schematic of the amplifier

By changing the current 12 the cascode current will change and the transconshyductance gm2 will change thus changing the amplifier gain With a fixed disshycriminator threshold that will change the discriminator sensitivity

The discriminator

The discriminator is a zero cross type chosen to obtain good timing with PM tu be signals in the 2mV to 60mV range After the amplification of the detector signal a short RC differentiation of IOns is applied to obtain a bipolar shape for the zero crossing discriminator There are three stages of amplification each with a gain of about 5 After the amplifier stages a differential comparator is used to provide the regenerCltion and the hysteresis The bipolar signal triggers the comparator 011 the leading edge aDd causes it to recover at zero crossing time with a fast trailing edge The comparator circuit is realized with an amplifier in which the load is replaced by a bistable regenerative circuit (Fig 3) The comparator is followed by a string of gates which perform logical differentiation and generate an output pulse of IOns on the comparator trailing edge The sensitivity of the discriminator is determined by thE variable gain of

the amplifier and a fixed threshold The offset of the comparator is controlled by the current of the second stage amplifier which defines the DC current of the comparator circuit The equivalent noise at the input is lt lOOfl V RMS The minimum threshold voltage is 2mV which provides amiddot satisfactory noise margin Normally the circuit is adjusted for a threshold of 25m Vat maximum

gain

OFTSET CONTROL

SK

2PF ~~___- -1

IK DI SC

2PF e---l f--- - I

SK

Fig 3

The time dispersion has been measured and the results for three different chips are given As the time dispersion depends on the signal amplitude (Fig 4) each measure has been convolved with the amplitude probability spectrum of the measured event (Fig 5) The results are presented in Fig 6

7lmemiddotam litude variaion

1685

168

JM5

LL-L-Li-----~J_I I I I I J bull I I l-L- 10 w ~ ~ n 40

Input nmpihJde (mV)

Fig 4 Zero-crossing time as a function of the input amplitude

A plot of a single photoelectron spectrum obtained with 950V at the PMT is presented in Fig5 It is evident from the plo that the noise of the linear chain is negligible and the single photoelectron spfctrum is well separated from the noise (below scale in the presented plot)

LALIRT 97-04 December 19gt7

A discriminator and shaper circuit realized In CMOS technology for BABAR

J Ardelean R L Chase A Hrisoho S Sen K Truong G Worms(r

Labomtoirr dr IA r-rfMralfllr Lineai1f JN2 PS- (N RS et lfniversitf Paris Sud F-91405 OTsoy FmnCf

J

Presented by A Hrisoho at the 7th Pisa Meeting on Advanced Detectors

La Biodola Isola dElba Livorno (Italy) May 25-31 1997

Abstract

An analog chip is designed to receive from a PM through a son coaxial cable signals rising in 3ns falling in Sns and to provide

digita signals for timing purposes multiplexed analog output proportional to the input for spectral measurements

There are 8 channels per chip with a common gain adjustment for the preamplifier and individual control for the offset and threshold setti ng TI1( discriminator senshysitivity is 2mV The dynamic range is from 2mV to IOOmV The noise equivalent at the input is ~ lOOlV The RMS time dispersion is less than SOOps for 3mV th reshold

The shaping amplifier is of bipolar s hape with Sans peaking time and 2 sV mean output voltage The crosstalk between cliannels is less than 2

1 Introduction

T he e lectroni cs chain is designed to record single photoelectron signals from P MTs with maximum efficiency and to note their arrival time with better than Ins precision which is necessary to reject background hits at the patshytern recogn ition level The desired time resolution is determined by the PMT time resolution of 18ns The e lectronic chain should not degrade this any further Since even background hits are also single photoelectron events thp

P MT amplitude does not carry any useful information for data analysis and is therefore registered on a multiplexed basis only for monitoring purposes As a conseq ue nce the disc riminator must acbiev its timing reso lution oVtr thp

2

3

whole PMT single photoelectron amplitude spectrum which covers the range from 2m V to 60mV at normal operating PMT high voltage

Circuit description

The circuit is designed to receive single photoelectron signals from a photoshymultiplier There are 8 channels on a CMOS technology ASIC with a digital output for timing and a multiplexed linear output for PMT gain monitoring A simplified diagram of the circuit is given on Fig 1

(CAIN CONTPOL

I N + Ol e

I ____bull ore OUT

IN-

p j

C I

IrN U

Tl = PI C I fa = K POI~~ bull CDI~~ T3 = K P3 bull C3

Fig 1 A simplified diagram of one channel

Each channel is composed of an amplifier with gain adjustment by a comshymon digital control for the 8 channels The amplifier differential output is followed by two buffers driving the discriminator circuit and the shaping cirshycuit respectively The discriminator is driven differentially whereas the shaper circuit is single-ended This has been done in order to minimize cross-talk to the neighboring channels in the fast discriminator part of the circuit and to compensate for temperature dependent threshold drifts which would affect the timing precision

The amplifier

It is a differential pair cascode in which the differential pair current is defined by the current source 11 and the cascode current is the difference [2 - Id2 of

2

4

the current sourCfS [2 aIld II respectively (Fig 2) The gClin of the amplifier is gi ven by

~ II gmi 1nmiddot (J)

gm2

Where gmi is the transconductance of the diffprential pair NMOS gm2 is the transconductance of the cascode load NMOS

j Il

-1

OUT u

GM2 -I

Fig 2 Schematic of the amplifier

By changing the current 12 the cascode current will change and the transconshyductance gm2 will change thus changing the amplifier gain With a fixed disshycriminator threshold that will change the discriminator sensitivity

The discriminator

The discriminator is a zero cross type chosen to obtain good timing with PM tu be signals in the 2mV to 60mV range After the amplification of the detector signal a short RC differentiation of IOns is applied to obtain a bipolar shape for the zero crossing discriminator There are three stages of amplification each with a gain of about 5 After the amplifier stages a differential comparator is used to provide the regenerCltion and the hysteresis The bipolar signal triggers the comparator 011 the leading edge aDd causes it to recover at zero crossing time with a fast trailing edge The comparator circuit is realized with an amplifier in which the load is replaced by a bistable regenerative circuit (Fig 3) The comparator is followed by a string of gates which perform logical differentiation and generate an output pulse of IOns on the comparator trailing edge The sensitivity of the discriminator is determined by thE variable gain of

the amplifier and a fixed threshold The offset of the comparator is controlled by the current of the second stage amplifier which defines the DC current of the comparator circuit The equivalent noise at the input is lt lOOfl V RMS The minimum threshold voltage is 2mV which provides amiddot satisfactory noise margin Normally the circuit is adjusted for a threshold of 25m Vat maximum

gain

OFTSET CONTROL

SK

2PF ~~___- -1

IK DI SC

2PF e---l f--- - I

SK

Fig 3

The time dispersion has been measured and the results for three different chips are given As the time dispersion depends on the signal amplitude (Fig 4) each measure has been convolved with the amplitude probability spectrum of the measured event (Fig 5) The results are presented in Fig 6

7lmemiddotam litude variaion

1685

168

JM5

LL-L-Li-----~J_I I I I I J bull I I l-L- 10 w ~ ~ n 40

Input nmpihJde (mV)

Fig 4 Zero-crossing time as a function of the input amplitude

A plot of a single photoelectron spectrum obtained with 950V at the PMT is presented in Fig5 It is evident from the plo that the noise of the linear chain is negligible and the single photoelectron spfctrum is well separated from the noise (below scale in the presented plot)

2

3

whole PMT single photoelectron amplitude spectrum which covers the range from 2m V to 60mV at normal operating PMT high voltage

Circuit description

The circuit is designed to receive single photoelectron signals from a photoshymultiplier There are 8 channels on a CMOS technology ASIC with a digital output for timing and a multiplexed linear output for PMT gain monitoring A simplified diagram of the circuit is given on Fig 1

(CAIN CONTPOL

I N + Ol e

I ____bull ore OUT

IN-

p j

C I

IrN U

Tl = PI C I fa = K POI~~ bull CDI~~ T3 = K P3 bull C3

Fig 1 A simplified diagram of one channel

Each channel is composed of an amplifier with gain adjustment by a comshymon digital control for the 8 channels The amplifier differential output is followed by two buffers driving the discriminator circuit and the shaping cirshycuit respectively The discriminator is driven differentially whereas the shaper circuit is single-ended This has been done in order to minimize cross-talk to the neighboring channels in the fast discriminator part of the circuit and to compensate for temperature dependent threshold drifts which would affect the timing precision

The amplifier

It is a differential pair cascode in which the differential pair current is defined by the current source 11 and the cascode current is the difference [2 - Id2 of

2

4

the current sourCfS [2 aIld II respectively (Fig 2) The gClin of the amplifier is gi ven by

~ II gmi 1nmiddot (J)

gm2

Where gmi is the transconductance of the diffprential pair NMOS gm2 is the transconductance of the cascode load NMOS

j Il

-1

OUT u

GM2 -I

Fig 2 Schematic of the amplifier

By changing the current 12 the cascode current will change and the transconshyductance gm2 will change thus changing the amplifier gain With a fixed disshycriminator threshold that will change the discriminator sensitivity

The discriminator

The discriminator is a zero cross type chosen to obtain good timing with PM tu be signals in the 2mV to 60mV range After the amplification of the detector signal a short RC differentiation of IOns is applied to obtain a bipolar shape for the zero crossing discriminator There are three stages of amplification each with a gain of about 5 After the amplifier stages a differential comparator is used to provide the regenerCltion and the hysteresis The bipolar signal triggers the comparator 011 the leading edge aDd causes it to recover at zero crossing time with a fast trailing edge The comparator circuit is realized with an amplifier in which the load is replaced by a bistable regenerative circuit (Fig 3) The comparator is followed by a string of gates which perform logical differentiation and generate an output pulse of IOns on the comparator trailing edge The sensitivity of the discriminator is determined by thE variable gain of

the amplifier and a fixed threshold The offset of the comparator is controlled by the current of the second stage amplifier which defines the DC current of the comparator circuit The equivalent noise at the input is lt lOOfl V RMS The minimum threshold voltage is 2mV which provides amiddot satisfactory noise margin Normally the circuit is adjusted for a threshold of 25m Vat maximum

gain

OFTSET CONTROL

SK

2PF ~~___- -1

IK DI SC

2PF e---l f--- - I

SK

Fig 3

The time dispersion has been measured and the results for three different chips are given As the time dispersion depends on the signal amplitude (Fig 4) each measure has been convolved with the amplitude probability spectrum of the measured event (Fig 5) The results are presented in Fig 6

7lmemiddotam litude variaion

1685

168

JM5

LL-L-Li-----~J_I I I I I J bull I I l-L- 10 w ~ ~ n 40

Input nmpihJde (mV)

Fig 4 Zero-crossing time as a function of the input amplitude

A plot of a single photoelectron spectrum obtained with 950V at the PMT is presented in Fig5 It is evident from the plo that the noise of the linear chain is negligible and the single photoelectron spfctrum is well separated from the noise (below scale in the presented plot)

4

the current sourCfS [2 aIld II respectively (Fig 2) The gClin of the amplifier is gi ven by

~ II gmi 1nmiddot (J)

gm2

Where gmi is the transconductance of the diffprential pair NMOS gm2 is the transconductance of the cascode load NMOS

j Il

-1

OUT u

GM2 -I

Fig 2 Schematic of the amplifier

By changing the current 12 the cascode current will change and the transconshyductance gm2 will change thus changing the amplifier gain With a fixed disshycriminator threshold that will change the discriminator sensitivity

The discriminator

The discriminator is a zero cross type chosen to obtain good timing with PM tu be signals in the 2mV to 60mV range After the amplification of the detector signal a short RC differentiation of IOns is applied to obtain a bipolar shape for the zero crossing discriminator There are three stages of amplification each with a gain of about 5 After the amplifier stages a differential comparator is used to provide the regenerCltion and the hysteresis The bipolar signal triggers the comparator 011 the leading edge aDd causes it to recover at zero crossing time with a fast trailing edge The comparator circuit is realized with an amplifier in which the load is replaced by a bistable regenerative circuit (Fig 3) The comparator is followed by a string of gates which perform logical differentiation and generate an output pulse of IOns on the comparator trailing edge The sensitivity of the discriminator is determined by thE variable gain of

the amplifier and a fixed threshold The offset of the comparator is controlled by the current of the second stage amplifier which defines the DC current of the comparator circuit The equivalent noise at the input is lt lOOfl V RMS The minimum threshold voltage is 2mV which provides amiddot satisfactory noise margin Normally the circuit is adjusted for a threshold of 25m Vat maximum

gain

OFTSET CONTROL

SK

2PF ~~___- -1

IK DI SC

2PF e---l f--- - I

SK

Fig 3

The time dispersion has been measured and the results for three different chips are given As the time dispersion depends on the signal amplitude (Fig 4) each measure has been convolved with the amplitude probability spectrum of the measured event (Fig 5) The results are presented in Fig 6

7lmemiddotam litude variaion

1685

168

JM5

LL-L-Li-----~J_I I I I I J bull I I l-L- 10 w ~ ~ n 40

Input nmpihJde (mV)

Fig 4 Zero-crossing time as a function of the input amplitude

A plot of a single photoelectron spectrum obtained with 950V at the PMT is presented in Fig5 It is evident from the plo that the noise of the linear chain is negligible and the single photoelectron spfctrum is well separated from the noise (below scale in the presented plot)

the amplifier and a fixed threshold The offset of the comparator is controlled by the current of the second stage amplifier which defines the DC current of the comparator circuit The equivalent noise at the input is lt lOOfl V RMS The minimum threshold voltage is 2mV which provides amiddot satisfactory noise margin Normally the circuit is adjusted for a threshold of 25m Vat maximum

gain

OFTSET CONTROL

SK

2PF ~~___- -1

IK DI SC

2PF e---l f--- - I

SK

Fig 3

The time dispersion has been measured and the results for three different chips are given As the time dispersion depends on the signal amplitude (Fig 4) each measure has been convolved with the amplitude probability spectrum of the measured event (Fig 5) The results are presented in Fig 6

7lmemiddotam litude variaion

1685

168

JM5

LL-L-Li-----~J_I I I I I J bull I I l-L- 10 w ~ ~ n 40

Input nmpihJde (mV)

Fig 4 Zero-crossing time as a function of the input amplitude

A plot of a single photoelectron spectrum obtained with 950V at the PMT is presented in Fig5 It is evident from the plo that the noise of the linear chain is negligible and the single photoelectron spfctrum is well separated from the noise (below scale in the presented plot)

tile IrHIIO nil

ju~ __ __ __ _ Fig S Single photoelectron spectr llm at 3mV discriminator threshold

RMS TIME D ISPERSION FOR THReF DIFTlcRHIT CHIPS Threshold=2mV SenSlollty==25mV

--- ~

--

~~ - X

10 Channel N

Fig 6 RMS time dispersion for threp different chips

The time dispersion has been meas ured also using a pulsed LED and a fiber on the photocathode to produce single photoelectrons The result of the meashysurement is given in Fig 7 The RMS dispersion is

rI=FWFIMj236 ~ Jns (2)

including the PMT

TOC lime Hlstolttrams I

1JO

(l C9

III

11

) l0

_14 11 j I 1 10 J) 6 19 11 lj 11 I I 3 3 40 4) 4amp 9 51 SJ 51 61 60t SOO f$b tI

F ig 7 Time dispersion resolution

The t ime variation has been measured as a function of t he temperature and the results are g iven in Fig 8

TIME VARIATION ps A FUNCTION (y TEMPERATURf

500115

i

r

0

f----i

I

shy r----shy o 10 20 30 40 50 fiO 70 80 90 middotC

Fig 8 Time variation lt1-lt a function of ambient tempe rature

A typical sensit ivi ty curve obtained by measuring the efficiency of the discrimshyinator is given in Fig 9

One can see from the effic iency curve that the voltage interval between zero output and max output frequency corresponds to plusmn 3a of the outpu t RMS noise T hese is a measure for the equivalent output noisf whic h will be ~ 100LV

5

___-Ally~pll~ LcO~rvlten0I1e~alta~ogtiJ-cihiI-f_----middot cacose~nsCjviifYi 100 I

~ ~ laquol 80

J()

20

225 15 275 J2 (j JJ 375 4 425

Inpul amplirude (m V)

Fig 9 Efficiency of the discriminator as a function of the input amplitude

Shaping amplifier

The shaping amplifier is designed to have a peaking time of about 80ns It makes use of current convertors (ICON circuit [lJ [2]) to increase the effective value of the resistors defining the shaping differentiation and integration time constants (Fig 10)

voo

OIlT

LoI=K l l

V5 S

Pig 10 ICON amplifier llse riogt resistor transformation circllit

The first integration of the shaper is driven by tJlf OIltpUt buffer of tlw common

7

amplifier circuit The differentiatioll the second integration and the third integration are realized by an ampl ifying stage using ICON current convertors with current division of 10 (Fig 11) i pboto of the output signal with and without the triggered discri m inator is given in Fig 12

R3

Rl

r--t~ ANALOG OUT

C1

I rltgtNO c~o

Tl = R1 gtIlt C1 T2 K gtIlt ROIFF gtIlt COIFF T3 K R3 C3

Fig 11 Si In pJjfi eci d iagrarn or the s l api ng am plifler

A bull he di~c(imjnaICH is nOI cri ggc lcrl

O 2~div

b - the discrimimnor i~ Iriggercd

Oljl sdiv

Fig 12 Analog shitper OlltpUt a - the discriminator is lOt triggered b - the disshycr-imillator is triggered

In Fig 13 the gain variat ion as (l function of the dlannd Humber for three different chips is given

8

5

___-Ally~pll~ LcO~rvlten0I1e~alta~ogtiJ-cihiI-f_----middot cacose~nsCjviifYi 100 I

~ ~ laquol 80

J()

20

225 15 275 J2 (j JJ 375 4 425

Inpul amplirude (m V)

Fig 9 Efficiency of the discriminator as a function of the input amplitude

Shaping amplifier

The shaping amplifier is designed to have a peaking time of about 80ns It makes use of current convertors (ICON circuit [lJ [2]) to increase the effective value of the resistors defining the shaping differentiation and integration time constants (Fig 10)

voo

OIlT

LoI=K l l

V5 S

Pig 10 ICON amplifier llse riogt resistor transformation circllit

The first integration of the shaper is driven by tJlf OIltpUt buffer of tlw common

7

amplifier circuit The differentiatioll the second integration and the third integration are realized by an ampl ifying stage using ICON current convertors with current division of 10 (Fig 11) i pboto of the output signal with and without the triggered discri m inator is given in Fig 12

R3

Rl

r--t~ ANALOG OUT

C1

I rltgtNO c~o

Tl = R1 gtIlt C1 T2 K gtIlt ROIFF gtIlt COIFF T3 K R3 C3

Fig 11 Si In pJjfi eci d iagrarn or the s l api ng am plifler

A bull he di~c(imjnaICH is nOI cri ggc lcrl

O 2~div

b - the discrimimnor i~ Iriggercd

Oljl sdiv

Fig 12 Analog shitper OlltpUt a - the discriminator is lOt triggered b - the disshycr-imillator is triggered

In Fig 13 the gain variat ion as (l function of the dlannd Humber for three different chips is given

8

amplifier circuit The differentiatioll the second integration and the third integration are realized by an ampl ifying stage using ICON current convertors with current division of 10 (Fig 11) i pboto of the output signal with and without the triggered discri m inator is given in Fig 12

R3

Rl

r--t~ ANALOG OUT

C1

I rltgtNO c~o

Tl = R1 gtIlt C1 T2 K gtIlt ROIFF gtIlt COIFF T3 K R3 C3

Fig 11 Si In pJjfi eci d iagrarn or the s l api ng am plifler

A bull he di~c(imjnaICH is nOI cri ggc lcrl

O 2~div

b - the discrimimnor i~ Iriggercd

Oljl sdiv

Fig 12 Analog shitper OlltpUt a - the discriminator is lOt triggered b - the disshycr-imillator is triggered

In Fig 13 the gain variat ion as (l function of the dlannd Humber for three different chips is given

8

GAIN DISPERSION FOR mREE DIrFERENT OIlFS

~L - - - --

-

shy

r--- - - --shy-+ _

i- - shy

-_ -_ -- _ - - - --- --- ---- - --_ _ -- 0

(~ rIRnnel Ndeg

Fig 13 Glttin variation as a function of th e channel number

6 Conclusions

The chip has been realized and the main problems of a mixed (analog and digital) ASIC concerning crosstalk to the analog part from the digital signals has been solved The minimum discriminator threshold is 2mV and the input noise is lOOuV Crosstalk between channels has been reduced to negligible values This performance has been obtained by careful separation in the lay out of the anaJog and digita1 parts and by extensive use of ground layers and multiple ground connections from the chip to the package

7 References

[1] J C Santiard et at Gasplex Analog Signa Processing for readout of Gessoes Detector Rap CERN -ECP 94 -17

[2] R L Chase A Hrisoho and J P Richer 16-channel CMOS preamplifier and shaper with adjustable peaking-time and automatic pole-zero cancellashytion Presented at the 7th Pisa Meeting May 25-31 J997