1WOLTE 96, LEUVEN, BELGIUM, 26-28 JUNE, 1996

CRYOGENIC ASICs IN GaAs FOR APPLICATIONS WITH PARTICLE

DETECTORS

Daniel Victor Camin and Gianluigi Pessina

Dipartimento di Fisica dell’Università and INFN Istituto Nazionale di Fisica Nucleare

Via Celoria 16, 20133 Milano, Italy

A SINGLE-ENDED/

DIFFERENTIAL VOLTAGE

SENSITIVE PREAMPLIFIERFOR

VERY LOW TEMPERATURE DETECTORS

A

BUFFER/SHAPER

LED DRIVER

FOR

LIQUID ARGON

CALORIMETER

MOTIVATIONS

Many applications with cryogenic particle detectors require touse a front-end electronic capable to work close to the detector, to minimise parasitic effects.

We present two examples of monolithic preamplifiers designedand realised for two different detectors:

2WOLTE 96, LEUVEN, BELGIUM, 26-28 JUNE, 1996

HOW A THERMAL DETECTOR OPERATES:

EXAMPLE: A BOLOMETRIC DETECTOR

CHARACTERISTICS: IF THE ABSORBING CRYSTAL HAS A LARGE MASS THE THERMALCONDUCTANCES KT AND KG LIMIT THE SIGNAL BANDWIDTH TO A FEW TENS OFHz.

IF THE BOLOMETER IS SMALL ITSSIGNAL BANDWIDTH IS LIMITED TO A FEW kHz BY THE SPEED OF SOUND AND THE THERMAL CONDUCTANCE Ke.

CT

K

K K

G

T B

C e

+

_

Δv

KEL

ΙIMPINGINGPARTICLE

CB

ΔT = ECT

Abso

rbin

gC

ryst

al

Ke

ThermistorLattice Electron Gas

wThe absorbing crystal heats up of an amount E/CT.

wThe temperature relaxation after the absorbed energy is throw KTand KG.

wThe temperature flow throw KG heats up the Thermistor lattice.

wThe flow throw Ke, inside the Thermistor, in turn heats up the electron gas temperature.

wA modification of the electron gas resistance occurs.

wA change in the voltage across the biased resistance is measuredproportional to the initial temperature increase.

BASE TEMPERATURE 10÷100mK

3WOLTE 96, LEUVEN, BELGIUM, 26-28 JUNE, 1996

WHY A SINGLE-ENDED/DIFFERENTIAL MONOLITHICPREAMPLIFIER FOR 4.2K TEMPERATURE

A VERY IMPORTANT SOURCE OF NOISE: VIBRATIONS OF THEELECTRICAL LINK

cP

AB

SO

RB

ING

CR

YS

TAL

TEMPERATURESENSOR

MECHANICALVIBRATIONS OFWIRES

THE FREQUENCY SPECTRUM OF THIS NOISE SOURCESIS WELL INSIDE THE SIGNAL BANDWIDTH OF THESE DETECTORS.

The fluctuations of the wire change the parasitic capacitance CP ofthe link, inducing a charge signal on the temperature sensor, which increases the temperature and develops an unwantedsignal voltage.

SINGLE-ENDED PREAM.:USEFUL WHEN THE SENSOR HAS A LOW IMPEDANCE (Tunnel Junction, TransitionThermometers, etc..): charge injection hasminimal effect.

cP

AB

SO

RB

ING

CR

YS

TAL

TEMPERATURESENSOR

+

-

cP

DIFFERENTIAL PREAM.:USEFUL WHEN THE SENSOR HAS A LARGEIMPEDANCE(Thermistors): chargesinjection generates the same signal at the pream. inputs, which gives no effects on the thermistor. At the output it cancels.

4WOLTE 96, LEUVEN, BELGIUM, 26-28 JUNE, 1996

PREAMPLIFIER CONCEPT

++ __RBRB

RA RA

A

VEE

RG

SINGLE-ENDEDDIFFERENTIAL SWITCH

A B

4 TWO SINGLE ENDED PREAMPLIFIERS ARE SYMMETRICALLY JOINED AT LINE A.

4 EACH PREAMPLIFIER HAS ONLY ONE MESFET AT THE INPUT, SAVING NOISE.

4 IF THE SWITCH IS CLOSED THE TWO PREAMPLIFIER ARE MADE INDEPENDENT: THEY BEHAVE AS A TWO CHANNELPREAMPLIFIER.

4 IF THE SWITCH IS OPEN THE PREAMPLIFIERS BEHAVE ASA DIFFERENTIAL INSTRUMENTATION PREAMPLIFIER AND RESISTOR RG SINK THE STANDING CURRENT.

5WOLTE 96, LEUVEN, BELGIUM, 26-28 JUNE, 1996

SINGLE-ENDED CIRCUIT PREAMPLIFIER CONCEPT

Vcc

IN+

OUT+

RB

OFFSET ADJUST

RA

RB

RA

+ _

VEE

VEE

A

A: The input MESFET Qi is Bootstrapped by Q1

Qi

Q1

Q2

B: Q2 cascodes the input bootstrap.

B

C

C: Active load, a bootstrapped current source

D

D: Common Source stage with active load andbuffer driver.

RC

Q1

Qi

Q2

Q3

Q3

Q4

Q4

6WOLTE 96, LEUVEN, BELGIUM, 26-28 JUNE, 1996

VEE

VDD VDD

IN+ IN-

OUT+ OUT-

RARA

RB RB

OA

S2

S1

D1

RG

Q1

Q2

Q3

Q4

Q5

Q6

Q7

Q8RCR1

RV

IB

R2

OB

Qi Qi

DIFFERENTIAL CIRCUIT PREAMPLIFIER CONCEPTAND STATIC OPERATING SETTING

DIFFERENTIAL CONFIGURATION:

POSITIVE SUPPLY VOLTAGE: VCC ≥ 3V(BEST FOR NOISE 4V)

NEGATIVE SUPPLY VOLTAGE: VEE ≤ -1.5V(OFFSET DEPENDENT)

POWER DISSIPATION VCC=4V, VEE ≈ -2.5V, PD=37mW

SINGLE-ENDED CONFIGURATION:

POSITIVE SUPPLY VOLTAGE: VCC ≥ 3V(BEST FOR NOISE 3.5V)

A) NEGATIVE SUPPLY VOLTAGE: VEE ≤ -1.5V (S1 TO VEE, S2 TO GND)(OFFSET DEPENDENT)

POWER DISSIPATION, CASE B), VCC=3.5V, VEE ≈ 0.3V, PD=25mW (Total, for both channels)

B) NEGATIVE SUPPLY VOLTAGE: VEE FOR OFFSET COMPENSATION(S1 TO VEE , S2 TO D1)

7WOLTE 96, LEUVEN, BELGIUM, 26-28 JUNE, 1996

LAYOUT AND GEOMETRY

TWO MESFET CAN BE PUT IN PARALLEL,EACH ONE HAVING LxG= 3x6000μm2

THE 2 CHANNELSARE SEPARATEDTO AVOID CROSSTALK.

Hf

Af

0.1

1

10

100

1 10

Lg (μm)

Af(1

0-12 V2 )

0.1

1

10

100

Hf(10

-26 J)

T = 4KID = 50 μAVDS = 100 - 250 mV

WHY WE USE L=3μm?

δα

vG2 I

DSVDS

L2 V

GS 1gm

2=( )

f

INPUT SERIES LOW FREQUENCY NOISE:

gm gm0W

A +B L=

FOR A MESFET (FOR WHICHELECTRIC FIELD SATURATIONIN THE CHANNEL OCCURS):

( )δα

vG2 I

DS0 V

DS 1gm0

2 A+B L 2

L2 V

GSW

=( )

fTHEN:

EXPERIMENTS:

2mm

2.5mm

(AT LEAST WITHSMALL LG)

8WOLTE 96, LEUVEN, BELGIUM, 26-28 JUNE, 1996

RESULTS AT 4.2K TEMPERATURE

1

10

100

1000

10 100 1000 10000

f (Hz)

nV/√Hz T=4kVcc=4V Vee=-2.6V

-0.7-0.5-0.3-0.10.10.3

0 100 200 300 400

VOUT (mV)

Err. %

606570758085

1 10 100 1000 10000

Hz

dB

1

10

100

1000

10 100 1000 10000

f (Hz)

nV/√Hz T=77kVcc=4V Vee=-2.

DIFFERENTIAL SIGNAL

FREQUENCY BANDWIDTH:ABOUT 3MHz

COMMON MODE REJECTIONRATIO.CROSS-TALK BETWEENCHANNELS IN SINGLE-ENDEDMODE WAS NOT MEASURABLE

75dB

INTEGRAL NON-LINEARITY

LESS THAN 0.3% IN THE 250mVOUTPUT VOLTAGE, CORRESPONDING TO ABOUT30mV OF DIFF. INPUT.THE GAIN IS 11

THE NOISE @ 4.2K HAS A 1/fSLOPE AT LOW FREQUENCY.INPUT MESFET WORKING POINTWAS: VDS≈ 0.4V, IDS=2.5mA.

90nV/√Hz@ 100Hz