1 / 23

Intro to Signal Processing cont’d

Intro to Signal Processing cont’d. Precision Pulse Generators. Popular ORTEC spectroscopy-grade precision pulse generators. Other brands: BNC, Tennelec , Canberra,.. Output signal amplitude is highly stable and varies linearly with dial/switch settings.

mac
Download Presentation

Intro to Signal Processing cont’d

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Intro toSignal Processingcont’d

  2. Precision Pulse Generators Popular ORTEC spectroscopy-grade precision pulse generators. Other brands: BNC, Tennelec, Canberra,.. Output signal amplitude is highly stable and varies linearly with dial/switch settings. Output pulse amplitude is calibrated independently in units of Volts, keV, etc. ANSEL Electronics 2

  3. PreAmp Amplifier Linearity Check: “Pulser Calibration” Series of signals from calibrated precision pulse generator fed into slow circuit. DAQ Det 2 V 0 V “Pulser Fence”calibrates abscissa of DAQ (Channel, Bin#) in Volts, MeV, etc. Pulser Amplitude (V) Counts ANSEL Electronics 2 Channel Number

  4. Analog-Digital (Fast-Slow) Circutry Trigger Data Acquisition ADC Logic Operations ANSEL Electronics 2 Actual Signal Ideal Signal Noise

  5. Analog-to-Digital Conversion (“Single Channel”) Integral Discriminator Integral DiscriminatorSingle-Channel Analyzer ANSEL Electronics 2

  6. Example: g-g Coincidence Setup Conditional Spectrum Intensity NaI Signal Amplitude NaI1 Source NaI2 ANSEL Electronics 2 e+e-2g511keV g 1.27MeV

  7. Principle of Operation Multi-Channel ADC More bits  higher resolution Need linearity:DE=const. DE E ADC Channel ANSEL Electronics 2 (Vin-Vref) /DE

  8. Uin Udisc t Uout Rf t R1 Udisc Uni/MonoVibrator +10V Input Output Discriminator/Trigger Task: Produce a logical signal, whenever analog signal exceeds threshold Udisc. Use for logical decisions (open acquisition,...). Exists for slow and fast pulses. ANSEL Electronics 2 Discriminator Threshold Potentiometer For fast timing, use negative NIM logic units

  9. Uin “walk” Udisc Udisc t Uout time jitter t Discrimination/Trigger Modes Task: Produce a logical signal, whenever analog signal exceeds threshold Udisc. Use for logical decisions (open acquisition,...). Exists for slow and fast pulses. Leading-edge timing:Trigger output signal appears at the time when signal crosses the threshold level on the leading edge. amplitude dependent! Uin t Uout Uin ANSEL Electronics 2 Zero-crossing timing:Trigger output signal appears at the time when bipolar signal crosses the base line.Independent of pulse amplitude! (Special case of constant-fraction timing) walk free Udisc Uout t

  10. +10V(±2 V) 0V “0” 0V ~2ns -16mA-0.8V/50W NIM Signal Standards (NIM: National Instruments Methods, TTL: Transistor-Transistor Logic) Linear analog NIM signals Slow logical NIM (TTL) pulses:discriminators, gates,… +10V “1” “1” +5V “0” TTL-Logic 0V ANSEL Electronics 2 NIM-gate/trigger signal Fast logical NIM signals for fast timing/triggering

  11. Examples: Digital Logics in ANSEL Experiments Common logical modules: Discriminators/TSCAFan In/Fan OutGate GeneratorDelay GeneratorLogical ANDLogical OR ANSEL Electronics 2

  12. Logic Chain: Fast NIM Modules U U t t Input: fast, narrow NIM signal Output: Long NIM/TTL “gate” signal ANSEL Electronics 2 Fan In/ Fan Out Module Gate & Delay Generator Fast Discriminator

  13. U1 U2 U1 U1 t t U2 U2 t t Uout Uout t t U U1 Uout=U1LU2 U U2 U2 Logic Modules Or (inclusive) Overlap Coincidence U1 Uout=U1VU2 Uout=U1LU2 U2 For fast timing: use fast negative logic ANSEL Electronics 2 complement Anti-Coincidence

  14. RF Signal Cables Amphenol RG58 coaxial cable (BNC) Impedance 50 Ohm Black PVC cable, tinned copper center conductor & braid for high frequency performance Nickel-plated connector body & Gold-plated center pin contact Insulation: Solid PE (Polyethylene) Rating < 500 V Outer Diameter: 0.195 inches nominal Velocity of Propagation: 66% (50ns/m) LEMO RG174 coaxial cable (LEMO) ANSEL Electronics 2

  15. Connectors for Coax Signal Cables BNCBayonet Neill-Concelman LEMOLéonMouttet Push-pull connectors “I”“Barrel” Bayonet mount locking mechanism ANSEL Electronics 2 LEMO“Elbow” “TEE”

  16. HV Supply Cables/Connectors MHV connectors: 5000voltsDC and 3 amperes. Hazards:HV on exposed central pin, ground disconnects before power.Do not use! SHVconnectors: Do not mate to BNC connectors, Power disconnects before ground. ANSEL Electronics 2

  17. outer casing outer conductor/shield inner conductor outer conductor dielectricmedium Signal Transmission z Coaxial cables/transmission lines  traveling waves in cavity resonators L: inductivity/lengthC: capacity/lengthdepend on diameter and dielectric Wave equation (R=0): signal propagation speed (speed of light): ANSEL Electronics 2 typically c-1=5 ns/m characteristic resistanceZ0=Ohmic resistance!For R≠0, Z0(w) complex Z0 = 50 W or 93 Wused for timing, spectroscopy, resp.

  18. Rd Rd Rload Rload Impedance Matching For impedance matching, Rload=Z0, cable looks infinitely long: no reflections from end. For mismatch, Rload ≠ Z0, reflection at end, traveling back, superimpose on signal receiver sender ANSEL Electronics 2 Polarity of reflected signal Rload=0, ∞

  19. Rterm Rload Cable Reflections Receiver input impedance Rload ≠ Z0,  use additional Ohmic termination in parallel Open end: Rload= ∞ Input and reflection equal polarity, overlap for t > 2Tcable Tcable = 2L/c L L Short: Rload=0, Input and reflection opposite polarity, superposition = bipolar ANSEL Electronics 2 Multiple (n) reflections attenuated by R-n

  20. The End ANSEL Electronics 2

  21. “walk” Udisc Pulse time jitter -1 Delay Td S Uin Trigger Uf=f·Uin Constant-Fraction Discriminator amplitude dependent leading edge discr. output timing Zero crossing timing always at same physical time, independent of pulse amplitude for fixed pulse shape: no “walk” with energy Ucftd ANSEL Electronics 2 Can utilize for PSD!

  22. Uin Udisc t Uout Rf t R1 Udisc Uni/MonoVibrator +10V Input Output Discriminator/Trigger Task: Produce a logical signal, whenever analog signal exceeds threshold Udisc. Use for logical decisions (open acquisition,...). Exists for slow and fast pulses. ANSEL Electronics 2 Discriminator Threshold Potentiometer For fast timing, use negative NIM logic units

  23. t t t Utrig Trigger output signal t Zero-Crossing Triggering Produce fast, bipolar linear pulse. Possible: different gains for positive and negative parts  zero crossing at different time (fraction of time to maximum) Produce “saturated” uniform pulse Differentiate saturated pulse, use triplet pulse as input for trigger (negative pulse polarity). Trigger output appears at zero crossing (Internal delays neglected) ANSEL Electronics 2

More Related