The Spectral Engine II (SEII) becomes part of a digital imaging, EDX, and/or WDS system as shown in this simplified diagram:

The 4pi hardware is marked in green. The SEII is a single card that plugs into a PCI slot on a Power Macintosh or Windows-based computer. The included Scanning Interface Unit (SIU), an external box, connects to the SEII via two D-sub 37-pin connectors and a double-shielded cable. The SIU connects to the electron microscope external scan control, the EDX pulse processor, and the WDS spectrometer counter outputs via cables that we supply. Optionally, the SEII (2.2rev2) can supply SCA outputs to the electron microscope for traditional x-ray dot mapping (blue).

4pi supplies Gresham pulse processors and x-ray detectors (red) for a complete EDX system, or supplies custom cabling to your existing system. Contact sales for more information.

A block diagram of the Spectral Engine II card is shown below. It connects to the Scanning Interface Unit (bottom of diagram) via a 37-pin cable. More information on the system architecture is available from 4pi support.

A block diagram of the Scanning Interface Unit is shown below. On one end, it connects to the Spectral Engine II card, on the other end it connects to: electron microscope scan control, pulse processor, and WDS counters.

Microscope Scanning and Control:

The Spectral Engine (SEII) creates line (X) and frame (Y) scan signals using 16-bit DACs. These signals are routed through Scanning Interface Unit (SIU) buffer amplifiers, each with independent front-panel gain and offset controls to match the scan amplitude to that required by the microscope scan circuitry. Using the Revolution software, the X-Y assignments can be reversed. The direction of each scan can be independently reversed as well. See the Hardware Setup Preferences in the Revolution Manual for more information.

The SEII uses a single enable signal to control a relay bank in the SIU. The relay bank connects to the microscope scan-control circuitry to provide external scan control activation and/or switching, CRT-blanking, and video-feedback signals.

The SIU provides a complete set of input and output connections for all control, blanking, and scan signals (not shown in the above diagram). This is required by some microscopes and also allows a 4pi system to be installed in series ("pass-through") with another scan control system. The SIU can switch the complete set of signals, allowing either the alternate scan control system or the 4pi system to control the microscope, all without removing any physical cables or connections.

The configuration of the SIU is determined before installation and is set at the factory. Typically, final adjustments to the scan video amplitudes must be made by the installer or customer. Both the final adjustments and virtually any configuration changes can be made easily by the end-user.

The SEII can create an image of any analog signal by digitizing that signal. The maximum allowed signal is ±15 volts. Typically the analog signal source is video from either a backscattered or secondary electron detector, but it can be an analog signal from any detector connected to the microscope (e.g., absorbed current, EBIC, or cathodoluminescence detectors).

4pi's digital imaging hardware must be able to access to the analog signal sources. Often these connections are available via panels supplied by the microscope manufacturer and are terminated with BNC or other standard connectors; however, this may not be the case if the microscope is not configured for external scan control. 4pi works with the customer and, if necessary, the electron microscope manufacturer to verify a microscope's external scan configuration. These details are resolved before the ordering process.

The SIU independently buffers up to 4 analog channels (Channels A, B, C, and D). Channel A has front-panel (external) fine-gain and offset controls and one internal coarse-gain control, while Channels B, C, and D each have internal gain and offset controls. These controls are typically used to set brightness and contrast independently of their instrument sources.

These 4 analog inputs are switched on the SEII card into a single ADC. The Revolution software controls the selection of the signals and the order in which they are read. The order of signal acquisition is determined by software settings. Refer to the SEM Image Preferences and SEM Linescan Preferences in the Revolution Manual for more information.

EDX:

Energy Dispersive X-ray Spectroscopy (EDX) is the technique of measuring the energies of x-rays emitted as the result of electron bombardment of a sample. PHA pulses from a pulse processor are buffered and gain/offset-adjusted by SIU circuitry and sent to the SEII, which precisely measures the amplitude of each pulse using a precision ADC and signal conditioning circuitry. The pulses are binned in 4096 channels, each channel corresponding to a range of x-ray energies (default 10eV per channel). Some pulse processors allow for direct connection without an SIU, if the system is EDX-only.

Software configuration of EDX operation is accessible from Revolution's X-ray Probe Preferences. The EDX and scanning/imaging capabilities of the SEII are independent; however, the two can be combined for x-ray mapping capability (see below) or collecting spectrum-per-pixel data sets for spectrum analysis.

Using the SIU, the SEII can be interfaced to a number of existing pulse processors, whose operation is known by Revolution's hardware setup. SIU circuitry buffers the signal for additional gain and offset control if the pulse processor does not have enough range.

X-ray Mapping:

X-ray mapping combines microscope scanning control and EDX spectrum acquisition to build an image of x-ray count intensity at each pixel for a particular ROI or set of ROIs. Software configuration changes specific to mapping are made in Revolution's X-ray Imaging Preferences.

WDS:

Wavelength Dispersive Spectroscopy (WDS) refines the EDX technique by using a crystal spectrometer to significantly narrow the detected X-ray energy linewidth. Typically, a single channel analyzer (SCA) generates TTL pulses, one for each x-ray detected by the crystal spectrometer. The SEII counts these pulses on any of four WDS counter inputs and Revolution creates a map based on the counts. Individual WDS counters are selected in Revolution just as for analog channel selection.

Functional Specification

• Up to 4 channels of digital imaging
• 4 channels of WDS mapping (optional)
• X-ray grayscale mapping
• 4096-channel MCA for EDX
• 16-channel SCA
• Advanced digital signal processing
• Images/maps up to 32k X 32k
• 16-bit (extendable to 40-bit) imaging/mapping pixel depth
• Full external scan control
• Variable image/map aspect-ratio
• Adjustable scan timing parameters
• 60/50 Hz synchronization
• Interface to a wide variety of SEM/S(T)EMs and pulse processors

Hardware Specification

• (4) 16-bit multiplexed analog channels
• (4) 16-bit TTL-compatible count channels
• (6) 20MHz Digital Signal Processors (120 MIPS)
• Dual 16-bit DACs
• Dual 12-bit 10MHz ADCs
• External scan control signals
• PHA Logic signals
• Independent imaging/PHA gain and offset control
• (16) single-channel analyzer outputs (optional)
• On-board PHA gain/offset trim

Software Compatibility

• 4pi Revolution (stand-alone, Macintosh and Windows 98/NT/2000/XP)
• FLAME (stand-alone, Macintosh and Windows 95/98/NT/2000)
• NIH Image (via plug-in, Macintosh only)
• Adobe Photoshop (via plug-in, Macintosh only)
• IPLab Spectrum (via plug-in, Macintosh only)
• DTSA (via plug-in, Macintosh only)

The Spectral Engine II (SEII) board can sequentially acquire up to four separate analog channels of 16-bit information. Commonly recorded digital imaging signals are from backscattered, secondary-electron, or absorbed current detectors. RGB outputs can be recorded to create color images. Other signals, such as cathodoluminescence or EBIC (electron beam-induced current) signals, can also be acquired. The 4pi Scanning Interface Unit (SIU) provides independent gain and offset controls for each channel if signals outside of the maximum range are required (voltage specs). Scan timing can be adjusted via software. WDS maps can be simultaneously acquired with digital images.

The SEII board can sequentially or simultaneously acquire up to four separate count channels (three on Windows) of 16-bit information (65,536 counts max). The TTL-compatible channels are trailing-edge triggered so that either positive- or negative-polarity pulses may be recorded. Count rates of well over 1Mhz operation are achievable, depending on configuration. Commonly recorded mapping signals are from user-supplied and operated Single Channel Analyzers (SCAs), for WDS mapping. Scan timing and count scaling can be adjusted via software. Digital images can be simultaneously acquired with WDS maps.

The SEII can acquire multiple 8- or 16-bit grayscale X-ray maps. K-, L-, and M- ROIs for each element (if applicable) are either pre-defined or can be defined by the user via software. The X-ray mapping functions use the on-board MCA to extract information about each region of interest. The ROIs are defined in software, so there is theoretically no limit to the number that can be created. Practical limits are enforced by the available memory; the number of ROIs is presently restricted in Revolution software to 106 elemental and 4 background. Contact support if you have different requirements. As in the case of digital imaging, the SIU provides scanning control. Digital images may be simultaneously acquired with X-ray maps, but the functionality depends on the software used (maximum flexibility is achieved with Revolution).

The Analog Devices ADSP-2171 Digital Signal Processor is the power behind the SEII. The SEII is broken up into two subsections, one to handle imaging and scanning functions, and the other to handle X-ray multichannel analysis (EDX) functions. A block diagram of the board shows this in more detail. Each DSP operates at 20 MIPS (million instructions per second). The master-slave-slave configuration allows both the imaging and the EDX subsection to each independently process data at 60 MIPS.

The Analog Devices ADSP-2171 digital signal processors allow the SEII to perform advanced processing tasks such as IIR and FIR filtering on the datastream as it is acquired. Programming hooks for these features are in place for future versions of Revolution.

Two DACs (digital-to-analog converters) are used on the imaging/mapping hardware subsection to generate horizontal and vertical scan signals. Each is the serial 16-bit Analog Devices AD1856, which is monotonic to 15 bits (32,768 positions).

• Any image or map size up to 32k x 32k can be defined. The ability to record large image or map sizes depends heavily on the amount of installed memory. The minimum width or length is 1 pixel, which can be used to define single linescans and will be used in Revolution to provide arbitrary linescan and lithographic capability.
• Special plug-in software note: NIH Image appears to have an odd feature which limits imaging line-scans to 16,382 pixels. Since NIH Image will crash if more pixels are acquired in a line, the current plug-in artificially limits the length of 16382 pixels. This limitation is in effect for Adobe Photoshop and IPLab Spectrum as well, but can in principle be removed. There is no such limitation for Revolution.

• The ADC (analog-to-digital converter) used on the imaging and EDX subsections of the hardware is either the Analog Devices AD872 or the AD9220. Functionally equivalent, both are 12-bit 10MHz ADCs.
• Digital images with 16 bits of pixel depth can be obtained by integrating for dwell times longer than the 100ns acquisition cycle of the ADC. Whereas dividing the integrated signal by the number of readings would normally throw away information, the SEII instead accumulates the information into a 16-bit buffer, thus retaining the maximum information.
• The DSPs can buffer up to 40 bits of image or map information per pixel; please inquire about custom applications if more than 16 bits of information are required.
• The X-ray spectrum acquisition subsection (EDX) is a 4096-channel (12-bit) MCA. Specially designed circuitry is used to achieve the required ultra-low differential non-linearity. The 2.2rev2 SEII has additional circuitry for software gain and offset trim adjustments.
• The X-ray mapping subsection makes no use of the imaging ADC, and instead borrows the 4096-channel MCA of the EDX subsection to extract information about the user-defined ROIs. The X-ray mapping function can record over 4 billion counts (32 bits of information) per pixel.

The SEII board alone provides two digitally-generated analog scan signals (horizontal and vertical - see voltage specs), a TTL external enable signal, and a TTL beam-blanking signal. To achieve full scan control beyond the board's capabilities, or to include beam or CRT blanking, the board must be paired with a 4pi Scanning Interface Unit.

The SEII board alone provides connections for TTL rate-in (fast-channel), rate-out (analog pulse-height analysis), TTL pulse-reject, TTL deadtime/livetime, and TTL ADC-busy logic signals, which can be interfaced directly to certain pulse processors. The SEII board can be connected to other pulse processors via the use of the external Scanning Interface Unit. 4Contact 4pi for more information.

• The 4pi Scanning Interface Unit provides independent gain and offset control for horizontal scan, vertical scan, up to 4 video channels (1 channel is standard), and the analog PHA channel.
• The 4pi Scanning Interface Unit provides full relay control for external scan enable and horizontal/vertical CRT blanking, and transfers all PHA, WDS, and beam-blanking logic to the SEII board.
• These features allow the SEII/SIU combination to be interfaced to a wide variety of electron microscopes and pulse processors.

The on-board SEII scan circuitry can be selected via software to define an aspect ratio that matches that of a microscope's CRT. The most common aspect ratios are 4:3 and 5:4. Non-integer aspect ratios can be selected. Aspect ratios less than one, used for certain microscopes (e.g., Hitachi), can also be defined.

• The SEII works by positioning the electron beam on a pixel-by-pixel basis, and dwelling at each point while image video, X-ray mapping, or WDS mapping information is collected. Dwell, interpixel delay, and horizontal and vertical retrace delays are set via software.
• Dwell: Electron image information is collected by the ADC every 100ns. For the imaging plug-in, the minimum dwell time is 1 microsecond; therefore, a minimum of 10 readings will be recorded at each pixel location in dwell mode. Revolution incorporates both dwell and sample averaging, and can also operate in single-reading mode for maximum speed. The maximum dwell time for imaging is 1600 microseconds for all software, and can be specified separately for each analog channel. Revolution allows special frame- and line-averaging modes for faster scanning.
• Interpixel Delay: After each beam position is sent to the scanning coil, this variable delay (0-800 microseconds) can be asserted to adjust for scanning artifacts before any data are recorded.
• Retrace Delays: Independent horizontal and vertical scan retrace delays can be specified (0-1600 microseconds). These controls eliminate scan retrace artifacts.
• The minimum dwell for X-ray slow mapping is 1 millisecond, and can be defined as real-time or live-time. Revolution provides an additional fast-mapping mode.
• The minimum dwell for WDS mapping is 1 microsecond, with a maximum of 16 seconds, and can be defined separately for each channel.

The SEII fast-scan can be synchronized to a 60 or 50 Hz waveform via a precise hardware timing mechanism. This does not remove 60 (or 50) Hz noise, but merely synchronizes it with the image so it is not apparent to the eye. The same effect can be achieved by tedious adjustment of the other adjustable scan timing parameters.

The SEII design incorporates the digital and logical signals required to interface to virtually every modern SEM/S(T)EM and pulse processor. The 4pi Scanning Interface Unit is designed to buffer the SEII signal levels and those of the microscope's scanning control unit and pulse processor.

The SEII 2.2rev2 board can act as a 16-output single-channel analyzer. SCAs are defined using x-ray mapping ROIs. The TTL-compatible output polarity can be set to positive or negative via a jumper on the board (applies to all 16 SCAs). Minimum pulse width is 1 microsecond, and can be increased to 2, 3, 4 microseconds (and so on) via software. Later versions of the SEII have, as an option, 4 SCA outputs.

The SEII 2.2rev2 board has the capability to trim both the offset and the gain of the PHA analog circuitry. The effect is small (± 10%), but has high resolution (sub-channel control). As such, it is not a substitute for course adjustment or calibration of the pulse processor.

• 4pi Revolution and FLAME are fully compatible with the SEII, and do not require plug-ins. Although Revolution does not access the plug-ins, its driver is backward-compatible with version 4.4.1 plug-ins.

• Via plug-ins (compatible only with Mac OS 8 and 9) supplied with the 4pi system, the user can acquire digital images, WDS maps, and X-ray maps into NIH Image, Adobe Photoshop, and IPLab Spectrum 3.1. Also via plug-in, the user can acquire EDX spectra into DTSA.

• See the software description for more information.

The following descriptions summarize the different SEII designs. A comparison to the Spectral Engine I is included for those considering upgrades.

• version 2.1 - identical in function to the NuBus-based 2.1 card described below. All hardware specs and details are described on this page.

• version 2.2rev1 - (not marked as rev1) same as 2.1 except added 16 SCA channels, changed certain voltage levels, and changed the board layout. The voltage changes may require the Scanning Interface Unit to be readjusted if one board is swapped out for another.

• version 2.2rev2 - same as 2.2rev1 and 2.1, except more voltage levels were changed along with more board-layout changes. The voltage changes may require the Scanning Interface Unit to be readjusted if one board is swapped out for another.

• version 1.0 - Imaging only

• version 2.1 - Imaging only, EDX-only, and Imaging/EDX combined

There is one hardware upgrade path and two software upgrade paths for the NuBus SEI:

• Hardware upgrade: the only path is to the 2.x SEII PCI card, since the 1.0 and 2.1 SEII NuBus cards are no longer made (see above).

• Software upgrade path 1: plug-ins. The 4.4.1 plug-ins will work with both the 1.0 and 2.1 NuBus and 2.x PCI card. The plug-ins are available as a free download from our site. A complete description and comparison can be found on our software page.

• Software upgrade path 2: Revolution. Revolution is 4pi's commercial application for image and x-ray spectrum and mapping acquisition. Revolution 1.5.6 is the most recent release; for more information see both our software page and the current Revolution feature list, or write to 4pi sales.

The design of the SEI is fundamentally different from the SEII. Comparisons can be difficult, but are summarized on the 4pi Software Capsule Comparison. The following list contains some broad descriptions and reminders that may be helpful in an evaluation.

• The SEI can only be used in a NuBus-based Mac. Of these, only the 7100 and 8100 models are PowerMacs.

• The SEI is incompatible with Revolution. Refer to the 4pi Software Capsule Comparison for details.

• The SEI x-ray acquisition speed is similar to the SEII 2.1 NuBus card under the DTSA plug-in. Likewise, the SEI x-ray mapping speed and is similar to the SEII 2.1 NuBus card under the XRayImageScan plug-in; however, the SEII feature set for x-ray acquisition and mapping is somewhat more advanced. Refer to the 4pi Software Capsule Comparison for details.

• Using the imaging plug-ins, The SEI digital image acquisition is slower than the the SEII 2.1 NuBus card under a variety of conditions, as shown in the table below (in seconds, red for SEI, blue for SEII):

  .	SEI frames			SEII NuBus Dwell
  Image Size	1	10	100	1µs	10µs	100µs
  256 x 256	2	13	112	2	3	9
  1024 x 1024	18	185	1747	17	26	122

  It is misleading to say that the SEII is "N-times faster" than the SEI, since the selection of a dwell time (SEII) or frame number (SEI) depends on a subjective notion of image quality. The results are virtually identical for both a Quadra 650 and a PowerMac 8100/80. This is expected since the Spectral Engine card does the bulk of the acquisition and averaging in all cases. Other speed comparisons, which include the PCI card, can be found in the 4.4 manual.

• The SEI digital-to-analog converters (DACs) are 12-bit (monotonic to 12), whereas the SEII DACs are 16-bit (monotonic to 15). The SEII can therefore address 32,768 individual scan positions, while the SEI can only address 4096 individual scan positions. Although this means the SEII has 8 times the resolution of the SEI, attempting to acquire such large images with the SEII is often impractical; the capability nevertheless remains.

• The SEI cannot do wavelength-dispersive mapping, micron markers, 50-60 Hz line sync, or more sophisticated averaging. Although the SEI can do multi-channel digital image acquisition, it is limited to either a 1-channel or a 3-channel mode, and does not provide complete control over the channel parameters. The SEII with plug-ins can provide 4-channel control, but is still limited because only one digital image can be collected with x-ray maps. Only the Revolution provides maximum control and flexibility for multi-channel digital imaging and x-ray mapping. Refer to the 4pi Software Capsule Comparison for details.