Download D. Other Pulse Shaping Methods

Pulse Processing and
Shaping
Amin Bagheri
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I. DEVICE IMPEDANCES
II. COAXIAL CABLES:
A. Cable Construction
B. Cable Properties
C. Noise Pickup and Component Grounding
D. Characteristic Impedance and Cable Reflections
E. Useful Coaxial Cable Accessories:
1. TERMINATORS
2. PULSE ATTENUATOR
3. PULSE SPLITTER
4. INVERTING TRANSFORMER
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III. PULSE SHAPING
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A. CR and RC Shaping:
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1. CR DIFFERENTIATOR OR HIGH-PASS FILTER
2. RC INTEGRATOR OR LOW-PASS FILTER
3. CR-RC SHAPING
4. GAUSSIAN OR CR-(RC)" SHAPING
5. ACTIVE FILTER PULSE SHAPING
6. TRIANGULAR SHAPING
7. TRAPEZOIDAL SHAPING
B. Pole-Zero Cancellation
C. Baseline Shift:
1. THE ORIGIN OF THE PROBLEM
2. BASELINE RESTORATION
D. Other Pulse Shaping Methods:
1. DOUBLE DIFFERENTIATION, OR CR-RC-CR SHAPING
2. SINGLE DELAY LINE (SDL) SHAPING
3. DOUBLE DELAY LINE (DDL) SHAPING
I. Device Impedances
II. Coaxial Cables
A. Cable Construction
B. Cable Properties
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The velocity of propagation for pulses through a coaxial
cable is a function only of the dielectric materials separating
the central conductor and the outer shield and is inversely
proportional to the square root of the dielectric constant
In signal cables, the important specifications are usually
the characteristic impedance and the capacitance per unit
length
In cables intended to carry bias voltage to detectors, the
maximum voltage rating is also important.
For transmission of fast rise time pulses, some attention
should be paid to the high-frequency attenuation
specifications of the cable.
C. Noise Pickup and Component
Grounding
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When components are physically separated, however, the shield
will tend to establish a common ground potential for all
components
Computers are a potential source of high frequency noise
pickup and may need to be kept at a distance from detectors
and preamplifiers where signal levels are low
A technique known as common mode rejection is sometimes
helpful in reducing the effects of noise pickup on
interconnecting cables.
D. Characteristic Impedance and Cable
Reflections
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pulse transmission through coaxial cables:
low-frequency or slow pulses
high-frequency or fast pulses
Pulses having rise times that are large compared with the
transit time are slow pulses, whereas those having a rise time
comparable to or shorter than the transit time are fast
pulses.
For slow pulses, the important properties are its series resistance
and capacitance to ground.
the most significant parameter usually is the cable capacitance.
For fast pulses, the important propertie is characteristic
impedance of the cable
Characteristic Impedance
Characteristic Impedance
E. Useful Coaxial Cable
Accessories:
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1. Terminators
2. Pulse Attenuator
3. Pulse Splitter
4. Inverting Transformer
III. PULSE SHAPING
A. CR and RC Shaping:
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1. CR DIFFERENTIATOR OR HIGH-PASS FILTER
--->
1. CR DIFFERENTIATOR OR HIGH-PASS FILTER
2. RC INTEGRATOR OR LOW-PASS FILTER
--->
3. CR-RC SHAPING
4. GAUSSIAN OR CR-(RC)" SHAPING
5. ACTIVE FILTER PULSE SHAPING
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Alternative methods are available to the circuit designer to carry out
similar operations using active circuits that incorporate elements such
as transistors and diodes.
6. TRIANGULAR SHAPING
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It is practically impossible to achieve a triangular shape using passive
circuit elements alone
B. Pole-Zero Cancellation
C. Baseline Shift:
1. THE ORIGIN OF THE
PROBLEM:
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for pulses from radiation
detectors, both the amplitude
and spacing are variable and
the degree of baseline shift is
not constant and no adequate
compensation can be carried
out.
baseline shifts can be
eliminated if the pulse shape is
made to be bipolar rather than
monopolar.
Effects of baseline shifts could
also be avoided if all elements
were dc coupled
2. BASELINE RESTORATION
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One method to avoid baseline shift
is to use shaping networks that
produce bipolar pulses.
The switch is open only during the
duration of each pulse
the role of the switch is carried out
by diodes1l or by more complex
nonlinear circuitry
use of these circuits introduces
some degree of additional noise
into the system
To be effective, baseline
restoration must take place near the
end of the signal chain
D. Other Pulse Shaping Methods:
1.
DOUBLE
DIFFERENTIATION,
OR CR-RC-CR
SHAPING:
to achieve
a bipolar pulse shape
D. Other Pulse Shaping Methods:
2. SINGLE DELAY LINE
(SDL) SHAPING:
D. Other Pulse Shaping Methods:
3. DOUBLE DELAY LINE
(DDL) SHAPING:
Thank
you