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 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.
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.
Integrated Power and Interface Board
Amptek’s DP5X 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 and software to communicate. The DP5X itself has its own power supplied so only needs a +5 V DC input. When using the DP5X with Amptek detectors, the integrated power supplies for the detector and preamp are all that is needed.
The integrated power supply provides power to Amptek detectors and preamps using an external +5 VDC source. The USB interface cannot supply enough current to operate the detectors, so an external DC supply is required, which must be between 4.0 and 12 V.
DP5 with Amptek Detector/Preamp
Figure 4. DP5 and Amptek detector/preamp.
DP5
Figure 5. DP5
Figure 6. DP5 back connector view.