measure what is measurable, and make measurable what is not so. - galileo galilei

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asure what is measurable, and make measurable what is no - Galileo Galilei

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Measure what is measurable, and make measurable what is not so.

- Galileo Galilei

Supriya DasDepartment of Physics &Centre for Astroparticle Physics and Space Science Bose [email protected]

6th. Winter School on Astroparticle Physics (WAPP 2011)Mayapuri, Darjeeling

Pulse : How does it appear?

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 3

Direct detection Indirect detection

Flow through the processing electronics

Pulse : Where are the information?

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 4

Brief surges of current or voltage in which information may be contained in one or Brief surges of current or voltage in which information may be contained in one or more of its characteristics – polarity, amplitude, shape more of its characteristics – polarity, amplitude, shape etcetc..

Baseline Pulse height or Amplitude Signal width

Leading edge / Trailing edge Rise time / Fall time Unipolar / Bipolar

Pulse : How do they look?

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 5

Fast or slow?

Rise time – a few nanoseconds or less

Rise time – hundreds of nanoseconds orgreater

Analog or digital?

Amplitude or shape varies continuouslyProportionately with the information

• signal from microphone• signal from proportional chamber

Quantized information in discrete number of states (practically two)

• pulse after discriminator

Logic standards

O/P must O/P must deliverdeliver

I/P must I/P must acceptaccept

Logic 1 Logic 1 (high)(high)

-14 mA to -14 mA to

-18 mA-18 mA-12 mA to -12 mA to

-36 mA-36 mA

Logic 0 Logic 0

(low)(low)-1 mA to-1 mA to

+1 mA+1 mA-4 mA to-4 mA to

+20 mA+20 mA

O/P must O/P must deliverdeliver

I/P must I/P must acceptaccept

Logic 1 Logic 1 (high)(high)

+4 V to +4 V to

+12 V+12 V+3 V to +3 V to

+12 V+12 V

Logic 0 Logic 0

(low)(low)+1 V to+1 V to

-2 V-2 V+1.5 V to+1.5 V to

-2 V-2 V

TTLTTL ECLECL

Logic 1Logic 1

(high)(high)2 – 5 V2 – 5 V - 1.75 V- 1.75 V

Logic 0Logic 0

(low)(low)0 – 0.8 V0 – 0.8 V -0.90 V-0.90 V

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 6

Nuclear Instrumentation Module (NIM)

Fast negative NIM Slow positive NIM

Transistor-Transistor Logic (TTL) and Emitter Coupled Logic (ECL)

Preamplification

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 7

Pre-amplifier (Preamp) : (i) Amplify weak signals from the detector(ii) Match the impedance of the detector and next level of electronics.

Vin Vout

R1

R2

Vout = -(R2/R1) Vin

Voltage sensitive

Vin Vout

Cf

Cd

Vout = - Q/Cf

Charge sensitive

Signal transmission

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 8

Signal is produced at the detector – one needs to carry it till the DataAcquisition system – How? What are the things one needs to keep in mind?

• transmission of large range of frequencies uniformly and coherently over the required distance, typically a few meters.

For transmitting 2-3 ns pulse the transmission line have to be able to transmit signals with frequency up to several 100 MHz.

One solution (the best one), Coaxial cable :

Two concentric cylindrical conductors separated by a dielectric material – the outer conductor besides serving as the ground return, serves as a shield to the central one from stray electromagnetic fields.

)/ln(2

abL

)/ln(

2

abC

Typically C ~ 100 pF/m and L ~ few tens of H/m

Signal Transmission (contd.)

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 9

Characteristic Impedance : )/ln(600 abK

K

C

LZ

e

m

Q. All coaxial cables are limited to the range between 50 – 200 Why?

Reflection, Termination, Impedance matching:

Reflection occurs when a traveling wave encounters a medium where the speed of propagationis different.

In transmission lines reflections occur when there is a change in characteristic impedance.

Reflection coefficient = (R-Z)/(R+Z) , where R is the terminating impedance.

if R > Z, the polarity of the reflected signal is the same as the propagating signal and the amplitude of reflected signal is same or less as of that of the propagating signal

in limiting case of infinite load (i.e. open circuit), the amplitude of the reflected signal is the same of the propagating signal

if R < Z, the polarity of the reflected signal is the opposite to the propagating signal and the amplitude of reflected signal is same or less as of that of the propagating signal

in limiting case of zero load (i.e. short circuit), the amplitude of the reflected signal is the same of the propagating signal

More on all these during the practical session with Raghunandan Shukla

Pulse Shaping

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 10

Amplifier : Amplifies signal from preamp (or from detector) to a level required for the analysis / recording.

When you’re performing pulse height analysis i.e. you’re interested in theenergy information – the amplifier should have shaping capabilities.

Pulse shaping: Two conflicting objectives

Improve the signal to noise (S/N) ratio – increase pulse width Avoid pile up – shorten a long tail

Pile up No pile up

Pulse Shaping (contd.)

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 11

Pulse shaping : How does it work?

CR Differentiator : High pass filter

RC Integrator : Low pass filter

Pulse Shaping (contd.)

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 12

CR-RC Shaping

Pole zero cancellation

Pulse Shaping (contd.)

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 13

Fixed differentiator time constant 100nsIntegrator time constant 10, 30, 100 ns

Fixed integrator time constant 10 nsDifferentiator time constant inf, 100, 30, 10 ns

CR-RC Shaping

Pulse Shaping (contd.)

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 14

Baseline Shift

Pulse Shaping (contd.)

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 15

Bipolar pulse : Double differentiation or CR-RC-CR shaping

Two advantages : (i) solution to baseline shift (ii) zero-crossing trigger for timing

Pulse Shaping (contd.)

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 16

More advancement : Semi-Gaussian Shaping

Digitization of pulse height and time

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 17

Analog to Digital Conversion - ADC

Flash ADC

Vref

Digitaloutput

Input is applied to n comparators in parallel Switching thresholds are set by resistor chains 2n comparators for n bits

Advantage:

Short conversion time (<10 ns)

Disadvantages:

o limited accuracyo power consumption

ADC (contd.)

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 18

Starts with MSB (2n). Compares the input with analog correspondent of that bit (from DAC) ands sets the MSB to 0 or 1. Successively adds the next bits till the LSB (20). n conversion steps for 2n bit resolution.

Pulse stretcher Comparator Control LogicRegister + DAC

Successive approximation ADC

Advantage:

speed is still nice ~ s high resolution can be fabricated on monolithic ICs

Disadvantages:

o starts with MSB

ADC (contd.)

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 19

Wilkinson ADC

Charge memory capacitor till the peak Do the following simultaneously:

1. Disconnect the capacitor from input2. Switch the current source to linearly discharge the capacitor3. Start the counter to count the clock pulses till the capacitor is discharged fully (decision comes from comparator)

Advantage:

excellent linearity – continuous conversion

Disadvantage:

o slow : Tconv = Nch/fclock

Typically for fclock ~ 100MHz and Nch = 8192, Tconv ~ 10 s

Nch is proportional to pulse height

ADC (contd.)

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 20

Wilkinson ADC

Operation Timing diagram

ADC (contd.)

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 21

Analog to Digital Conversion – Hybrid technology

Use Flash ADC for coarse conversion : 8 out of 13 bits Successive approximation or Wilkinson type ADC for fine resolution Limited range, short conversion time 256 channels with 100 MHz clock – 2.6 s

Result: 13 bit conversion in 4 s with excellent linearity

Digitization of time (contd.)

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 22

Time Digitization : TAC, TDC

Counter:

Very simple : count clock pulses between START and STOP. Limitation : speed of counter, currently possible 1 GHz - time resolution ~ 1 ns

Analog Ramp:

charge a capacitor through current source START : turn on current source , STOP : turn off current source

use Wilkinson ADC to digitize the storage charge/voltage

Time resolution ~ 10 ps

Timing circuits

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 23

Discriminator : Generates digital pulse corresponding to analog pulseCombination of comparator and mono-shot.

Vth Comparator Monoshot

Problem : Time walk

Timing circuits (contd.)

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 24

Solution 1 : Fast zero crossing Trigger

Take the bipolar O/P from shaper/amplifierTrigger at zero crossing point

Advantage :

The crossing point is independent of amplitude

Disadvantage :Works only when the signals are of

same shape and rise time

Timing circuits (contd.)

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 25

Solution 2: Constant Fraction Trigger

Pulse processing - instruments

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 26

Physical/mechanical parameters :• width – 19” (full crate)• width of the slot – 1.35”• height – 8.75”

Electrical parameters :

+/- 24 V, +/- 12 V, +/- 6 V, +/- 3 V (sometimes) connectorconnector

NIM

Pulse processing - instruments

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 27

Once again 19” wide crate with25 slots/stations

2U fan tray

CAMAC – Computer Automated Measurement and Control

Main difference with NIM – computer interface

Back plane contains power bus as well as data bus

Station 24 & 25 reserved for the controller

Pulse processing - instruments

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 28

VME – Versa Module Eurocard (Europa)

Much more compact, high speed bus

Fiber optic communication possible

Developed in 1981 by Motorola

References

Supriya Das, Bose InstituteWAPP 2011, Mayapuri, Darjeeling 29

Many of the diagrams you’ve seen here are from

Radiation Detection and Measurement – G.F. Knoll Techniques for Nuclear and Particle Physics Experiments – W.R. Leo Nuclear Electronics – P.W. Nicholson Radiation Detection and Signal processing (lecture notes) – H. Spieler (http://www-physics.lbl.gov/~spieler/Heidelberg_Notes/) ORTEC Documentation - www.ortec-online.com

Thank You