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Overview The Amptek DP5 is a state of the art, high performance, low power digital pulse processor. It digitizes the preamplifier output signals, replacing both the shaping amplifier and MCA in a traditional, analog spectroscopy system. The DP5 offers several clear advantages over traditional systems, including improved performance (very high resolution, reduced ballistic deficit, higher throughput, and enhanced stability), enhanced flexibility, low power consumption, small size, and low cost. The DP5 implements the pulse processing using dedicated circuitry. It includes an 8051 compatible microcontroller for controlling the unit. Communication interfaces include RS232, USB, and Ethernet. Several general purpose I/O lines are also available. The DP5 is suitable for OEMs and for laboratory users who need custom capabilities and are familiar with electronics. Features 80 MHz ADC Replaces both shaping amplifier and MCA Supports both reset and feedback preamplifiers of either polarity MCS Mode 16 SCA's List Mode Configurable with a charge sensitive preamplifier for use with PMTs For OEM or custom laboratory use Highly configurable Pulse Processing & MCA Trapezoidal shaping Commandable peaking time from 0.1 to 102.4 µs Commandable flat top duration from 0.05 to 51.2 µs 4,000,000 cps periodic Pile-up rejection, risetime discrimination, gate Up to 8k output MCA channels Communications Interfaces: RS-232, USB, Ethernet Oscilloscope mode - DAC output for pulse monitoring and adjustment Onboard µcontroller with 8051-compatible core Many configurable auxiliary inputs & outputs available Software Free Display and Acquisition Software Free Software Developer's Kit (SDK) Physical Low Power: 600 mW typical Small Size: 3.5 in X 2.5 in Applications X-ray and gamma ray detectors Nuclear Instrumentation Portable, battery operated systems OEM & Special Applications Process Control Research and Teaching

Figure 1. DP5 Photo: 3.5 in. X 2.5 in. Figure 2. Trace 1 above shows the input to the DP5, which is the output from a reset-type charge sensitive preamplifier. This is processed by the analog prefilter producing the prefilter output shown in Trace 2. This is digitized and then processed digitally, producing the DP5’s shaped output shown in Trace 3. Finally, the DP5 creates a multichannel anlayzer (MCA) type output spectrum shown in Graph 4.

Specifications

Pulse Processing Performance

MCA Performance

Hardware

Communications

Auxiliary Inputs and Outputs

The primary purpose of this connector is to bring out logic signals which are not required for the primary use of the DP5: acquiring spectra and transmitting then over the serial interface. These are generally “low level” logic signal associated with each pulse processed by the DP5. They are primarily used for synchronizing the DP5 data acquisition to external hardware and for direct counter/timer outputs from the DP5. The signals are described below. The connector is a 2x8 right angle Samtec part number ASP-135096-01.

Auxiliary Connector Pin Assignments

Connections

Interface Software

Power

Physical

General and Environmental

DP5 Architecture

The DP5 is a component in the complete signal processing chain of a nuclear instrumentation system. The input to the DP5 is the preamplifier output. The DP5 digitizes the preamplifier output, applies real-time digital processing to the signal, detects the peak amplitude (digitally), and bins this value in its histogramming memory, generating an energy spectrum. The spectrum is then transmitted over the DP5’s serial interface to the user’s computer. Clearly, the DP5 must be used with other components, including a detector, preamplifier, and computer.

Figure 3. Block diagram of the DP5 in a complete system.

Analog Prefilter

The input to the DP5 is the output of a charge sensitive preamplifier. The analog prefilter circuit prepares this signal for accurate digitization. The main functions of this circuit are (1) applying appropriate gain and offset to utilize the dynamic range of the ADC, and (2) carrying out some filtering and pulse shaping functions to optimize the digitization.
NOTE: The DP5 can be ordered with a charge sensitive preamplifier on the board for use with PMTs.

ADC

The ADC digitizes the output of the analog prefilter at a 20 or 80 MHz rate (software selectable). The digitized values are sent, in real time, into the digital pulse shaper. 12 bit ADC is used.

Digital Pulse Shaper

The ADC output is processed continuously using a pipeline architecture to generate a real time shaped pulse. This carries out pulse shaping as in any other shaping amplifier. The shaped pulse is a purely digital entity. Its output can be routed to a DAC, for diagnostic purposes, but this is not necessary.

There are two are two parallel signal processing paths inside the DPP, the “fast” and “slow” channels, optimized to obtain different data about the incoming pulse train. The “slow” channel, which has a long shaping time constant, is optimized to obtain accurate pulse heights. The peak value for each pulse in the slow channel, a single digital quantity, is the primary output of the pulse shaper. The “fast” channel is optimized to obtain timing information: detecting pulses which overlap in the slow channel, measuring the incoming count rate, measuring pulse risetimes, etc. and to obtain

The DP5 uses trapezoidal pulse shaping, which offers high energy resolution, reduces ballistic deficit, and provides excellent baseline stability at high count rates.

Pulse Selection Logic

The pulse selection logic rejects pulses for which an accurate measurement cannot be made. It includes pile-up rejection, risetime discrimination, logic for an external gating signal, etc. At high count rates, the DP5 has both better pile-up rejection and higher throughput than a traditional, analog shaping amp.

Histogramming Memory

The histogram memory operates as in a traditional MCA. When a pulse occurs with a particular peak value, a counter in a corresponding memory location is incremented. The result is a histogram, an array containing, in each cell, the number of events with the corresponding peak value. This is the energy spectrum and is the primary output of the DP5. The unit also includes several counters, counting the total number of selected pulses but also counting input pulses, rejected events, etc. Auxiliary outputs include eight different single channel analyzers, and both a DAC output and a digital output showing pulse shapes from several points in the signal processing chain.

Interface

The DP5 includes hardware and software to interface between these various functions and the user’s computer. A primary function of the interface is to transmit the spectrum to the user. The interface also controls data acquisition, by starting and stopping the processing and by clearing the histogram memory. It also controls certain aspects of the analog and digital shaping, for example setting the analog gain or the pulse shaping time.

The interface includes a microcontroller that impliments RS232, USB, and Ethernet communications.

PC5 Power and Interface Board

Amptek’s DP5 Digital Pulse Processor is a component in the complete signal processing chain of a nuclear instrumentation system. It must be used with other components, including (at a minimum) a detector and preamplifier, and computer with a serial interface and software to communicate. The DP5 itself has its own power supplied so only needs a +5 V DC input. When using the DP5 with Amptek detectors, additional power supplies are needed for the detector and preamp. Amptek provides the PC5 board that mates with the DP5 and provides power to Amptek detectors.

The PC5 provides power to Amptek XR-100 detectors from a +5 VDC source. This board is intended for those using Amptek detectors and preamps. The USB interface cannot supply enough current to operate the XR100, so an external DC supply is required, which must be between 2.5 and 5.5 V.
Dimensions: 3.5 in. x 2.5 in.

Figure 5. DP5 (top) mated with the PC5 (bottom).

Figure 6. DP5 (bottom) mated with the PC5 (top), back connector view.

Software

The A250 Connected to a DP5 Digital Pulse Processor and MCA

Figure 9. The A250 charge sensitive preamplifier connected to the DP5 or PX5 digital pulse processor and MCA.

The DP5 Connected to a Germanium (HPGe) Detector

Figure 10. DP5 digital pulse processor connected to a Germanium (HPGe) detector. Various materials.

Figure 11. DP5 digital pulse processor connected to a Germanium (HPGe) detector. Various radioisotopes.

DP5G for use with Scintillators and Photomultiplier Tubes

The Amptek DP5G is a state-of-the-art, high performance, low power digital pulse processor designed for use in scintillation spectroscopy systems. Connected to the anode of a PMT, it includes a charge sensitive preamplifier and a digital pulse processor, which replaces both the shaping amplifier and the MCA in a traditional nuclear spectroscopy system. The DP5G offers several advantages over traditional systems, including higher performance, enhanced flexibility, small size, and low cost.

Figure 12. DP5G showin in actual size, 2 in. X 1.75 in.

The DP5G is one component in a complete gamma-ray spectrometer, shown in the diagram below. The DP5G includes only the core signal processing functions. A complete system must also include a detector module (scintillator, PMT, HV supply, tube base) and interface circuitry with power supplies and connectors for the serial connection. Amptek can provide an OEM user with the DP5G alone, or can provide it with a PCG interface module, or can provide a complete system, including the detector module. The complete system is a separate Amptek product, the Gamma-Rad5.

The DP5G represents the latest generation in digital pulse processing. The DP5G is a variant of the DP5, optimized for scintillation readout. The DP5 technology includes faster peaking times, improve pile-up rejection and pulse shape discrmination, better dead time correction, additional features such as a “List Mode,” and enhanced interfaces.

Figure 13. DP5G block diagram.

DP5G Charge Amplifier

The analog prefilter in the DP5G differs from that of Amptek's other digital processors: the first stage of the DP5G is a charge amplifier rather than a voltage amplifier. This difference has important implications for the performance of the DP5G and how one interfaces with it. The plot below shows the DP5G charge amplifier and how it is typically connected to a PMT.

Figure 14. DP5G Charge Preamp configuration.

1. Fast scintillators: The charge amplifier permits the DP5G to be used with scintillators having a very fast time constant. Customers often ask "Since the ADC operates at 80 MHz (12 ns), how can you measure a scintillator with a 10 ns decay time"? The current pulse Iin(t) into J2 may be fast, but the output of U11 is the time integral of Iin(t) (differentiated by a 3.2 µs time constant). A faster scintillator simply gives a faster rising edge to the output of U11. The figure below shows simulated results for three different time constants. The DP5G can accurately digitize very fast scintillators, because it is digitizing the output of the charge amplifier, not the input current.


Figure 15. Left: Simulated input currents for scintillators with 10 ns (red), 20 ns (blue), and 230 ns (black) time constants. Right: Simulated outputs for U11 for the same three cases.

2. Current input: The input to the DP5G must be a current, not a voltage. U11 integrates the current pulse from the PMT. Some users have inserted a transimpedance amplifier between the PMT and the DP5G, providing a voltage input to the DP5G. This will not work properly with the standard DP5G configuration. The user can reconfigure the circuit to handle voltage inputs but the standard DP5G requires an input current pulse.
3. PMT polarity: The figure above shows a positive HV on the PMT anode, with the cathode grounded. But the DP5G works fine if the cathode is held at a negative HV and the anode is at virtual ground. In both cases, a pulse of electrons is accelerated from the cathode and injected across the coupling capacitor into the DP5G.

DP5G Specifications

DP5 Specifications in PDF (500k)
Digital Pulse Processor FAQ
Reasonds to upgrade the DP5 to FW6
Glossary

Revised September 4, 2012