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XIA microDXP, Техническое справочное руководство

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microDXP Technical Reference Manual 

 

Version 3.15 

 

 

October 7, 2019 

 

39 

Another consideration with RC-feedback preamplifiers is the DC offset. Although many 
such  preamplifiers  produce  a  ground-referenced  output,  many  do  not.  Any  offset  is 
addressed  in  the  microDXP  by  automatically  adding  a  digitally  controlled  DC  offset 
voltage to the input signal, such that the baseline value corresponds to 10%  of the ADC 
input range. 

3.2.2  Analog Gain 

The overall gain transfer function defines the relationship between the input x-ray pulse 
height  and  the  resulting  MCA  bin,  or  measured  energy.  A  separate  document,  the 
microDXP  Gain  Specification,  describes  the  overall  gain  transfer  function  of  the 
microDXP, and includes examples. 

The  original  (green)  microDXP  used  an  off-the-shelf  variable  gain  amplifier  (VGA)  to 
implement  a  continuously  adjustable  analog  gain  for  both  dynamic  ranging  and  energy 
calibration. The single ‘base gain knob’ was easy to use, but we’ve found that VGA devices 
introduce excessive noise, temperature drift, and significant non-linearities into the signal.  

In a significant departure from the previous design, the updated (blue) microDXP design 
now  employs  a  digitally-controlled  switched-gain  amplifier  architecture  with  16  coarse 
analog gain settings for dynamic ranging in concert with finely adjustable digital gain for 
energy calibration. This approach adds some complexity to command and control because 
there  are  now  two  separate  ‘base  gain  knobs’,  but  yields  a  superior  pulse-height 
measurement. As before, a separate bin width setting defines the granularity, and thus the 
file size, of the MCA energy spectrum. A customer-defined fixed-gain hardware assembly 
option  is  available  in  volume  production  for  applications  where analog  gain  adjustment 
isn’t required. 

 

Figure 3-3: The new microDXP gain architecture 

The  Analog  Gain  includes  all  gain  elements  in  the  front-end  analog  circuitry,  i.e.  it 
determines the pulse-height at the ADC for a preamplifier pulse-height 

V

Preamp

: 

V

ADC

 = Analog Gain * 

V

Preamp 

Equation 3-2 

The  14-bit  ADC  has  an  input  range  of  2.0V,  thus  the  digitized  pulse  height  in  least-
significant-bits is: 

Содержание microDXP

Страница 1: ...761 http www xia com Information furnished by XIA LLC is believed to be accurate and reliable However no responsibility is assumed by XIA for its use or for any infringements of patents or other right...

Страница 2: ...11 1 2 2 Detector Preamplifier 11 1 2 3 Power Requirements 12 1 2 4 Operating Environment 12 1 2 5 Regulatory Compliance 12 1 3 Hardware Options 12 1 3 1 Communications and Power Interface 12 1 3 2 A...

Страница 3: ...ings 22 2 1 1 Preamplifier Type Selection 22 2 1 2 Input Signal Attenuation 22 2 2 Board State and Configuration 23 2 2 1 Board Information and Status 23 2 2 1 1 ADC Sampling Rate DSP Clock Speed DSPS...

Страница 4: ...meter Set 30 2 6 2 Download a Master Parameter Set 30 2 7 Data Acquisition 30 2 7 1 Starting a Run 31 2 7 2 Stopping a Run 31 2 7 3 Reading a Spectrum 31 2 7 4 Reading and Calculating the Run Statisti...

Страница 5: ...Parallel Flash EEPROM 44 3 5 2 Serial Port SPORT 44 3 5 3 DMA Port 44 3 5 4 DSP Code Variants 44 3 6 PIC Microcontroller 44 3 6 1 RS 232 Serial Port 45 3 6 2 I2C Serial Bus 45 3 6 3 I2C EEPROM 45 3 6...

Страница 6: ...ng 57 4 7 Pile up Inspection 58 4 7 1 Slow Pileup 59 4 7 2 Fast Pileup 60 4 8 Input Count Rate ICR and Output Count Rate OCR 61 4 9 Throughput 61 Appendices 63 Appendix A MicroDXP Hardware Specificati...

Страница 7: ...er supply in the 100VAC to 240VAC range at 50Hz or 60Hz Use of this development kit with AC voltage outside these specifications could damage the unit and nullify the product warranty Refer to Chapter...

Страница 8: ...bligated to furnish service under this warranty a to repair damage resulting from attempts by personnel other than XIA LLC representatives to repair or service the product or b to repair damage result...

Страница 9: ...ard sections of code file contents and syntax examples Setup exe refers to a file called setup exe on the host computer Italics Italic text denotes a new term being introduced or simply emphasis peaki...

Страница 10: ...ports custom auxiliary digital access including the industry standard I2C serial bus and four configurable digital I O lines The microDXP is thus a flexible cost effective OEM component that can form...

Страница 11: ...ry XIA provides the ProSpect software application for microDXP parameter set configuration intended for use both in evaluation and production phases 1 1 3 Custom OEM Features Customized firmware devel...

Страница 12: ...modest gamma or X ray flux above a certain level this radiation will start to cause bit errors in the digital components If necessary please contact XIA LLC to discuss a proposed radiation environment...

Страница 13: ...pplied directly either linear regulated or high quality switching supplies should be used If the on board LDO regulators are used a minimum of 5 50 V is required and the ripple requirement can be rela...

Страница 14: ...t the one percent level and only digital scaling is used for energy calibration The fixed gain option offers better performance in some cases and somewhat lower power consumption The analog gain is fu...

Страница 15: ...instrument s flexibility 1 5 1 Example 1 General Purpose USB Spectrometer with MicroComU Companion Board In this example the microDXP microComU board set acts as a general purpose spectrometer connect...

Страница 16: ...nal mechanical design i e enclosure design may be necessary The microDXP power supplies and routing adapter together constitute a spectrometer that can be connected to virtually any controller with RS...

Страница 17: ...e control 2 Customized PIC microcontroller code is required to implement high level data acquisition routines controlled through the user pushbutton interface 3 Customized DSP code is required for pea...

Страница 18: ...resides in the hardware and executes the command set 1 6 1 User Interface e g ProSpect The host software communicates with and directs the microDXP via a driver layer and displays and analyzes data a...

Страница 19: ...e firmware combination since most problems are actually solved at the software level Please check for the most up to date standard versions of the microDXP software and firmware at http www xia com mi...

Страница 20: ...conflict among themselves This can cause the DXP unit to report data that apparently make no sense such as bad peak resolution or even empty spectra Each time a problem is reported to us we diagnose i...

Страница 21: ...th the needs of our users Please send us your feedback regarding the functionality and usability of the microDXP and ProSpect software In particular we are considering the following development issues...

Страница 22: ...detector preamplifier for the first time 2 1 1 Preamplifier Type Selection The preamplifier type selector switch if present should already be set properly Note that the setting must agree with the fi...

Страница 23: ...d versions Select the Status tab to display information about the current state of the PIC DSP and data acquisition run The RS 232 command to read board information is 0x49 Please refer to the RS 232...

Страница 24: ...cessed via the Detector and Advanced tabs of the Settings panel Because these settings are global changes are simultaneously applied and saved to nonvolatile memory via the Apply Save button 2 3 1 Pre...

Страница 25: ...ing the delay longer than necessary introduces additional processor dead time which will reduce the data throughput at high count rates In ProSpect RESETINT is set via the Reset Interval field in the...

Страница 26: ...o define a spectrum that exceeds the practical limits of the ADC which should be avoided As a rule of thumb the product of Number MCA Bins and MCA Bin Width should not exceed 8192 If the product is la...

Страница 27: ...ched Gain and Digital Base Gain Please first review 3 2 2 for a description of the updated analog gain circuitry and digital gain coefficient and 2 2 1 2 to determine if the Switched Gain feature is i...

Страница 28: ...ven combination more than once The factory set default spectrometer settings should be adequate to acquire a recognizable spectrum To achieve optimal performance the spectrometer settings must be adju...

Страница 29: ...ging In ProSpect Baseline Average Length is accessed in the Acquisition tab of the Settings panel Select the desired multiple of 2 value from the drop down list Modifications for the selected PARSET c...

Страница 30: ...RS 232 command to save the current PARSET table is 0x8D Please refer to the RS 232 Command Specification for details 2 6 Repetitive Configuration of Identical Systems In cases where many microDXP card...

Страница 31: ...e entire spectrum Each MCA bin is represented in DSP program memory as a 24 bit word i e 3 bytes supporting up to 16 777 215 counts per bin In some cases i e for short runs and or low count rates the...

Страница 32: ...ely to units of 500 nanoseconds the process that monitors the real time and live time is only updated every 500 microseconds Similarly the input and output counts are tallied every 500 microseconds Th...

Страница 33: ...ntermediate Filter 3 The output of the intermediate baseline filter before baseline subtraction Baseline Samples 4 Samples of the raw intermediate filter when at baseline Baseline Average 5 A running...

Страница 34: ...on zero is crossed Intermediate Slow Trigger 2 A trigger is generated whenever the intermediate filter Baseline threshold if non zero or slow filter Energy threshold if non zero is crossed MCA Event 3...

Страница 35: ...command to read the baseline histogram is 0x10 The RS 232 command to read the baseline history is 0x12 Please refer to the RS 232 Command Specification for details 2 8 3 DSP Parameters The instantaneo...

Страница 36: ...memory The functions of each block are summarized below This chapter does assume the reader has some familiarity with x ray pulse processing theory and electronic devices Please see Chapter 4 of this...

Страница 37: ...ier output signal such that a moderately priced ADC can be used 3 2 1 1 Reset Type Preamplifiers For reset type preamplifiers the dynamic range reduction is accomplished using a novel technology for w...

Страница 38: ...h then remedies the situation by quickly closing the reset switch During this so called Tracking Step data passed to the FiPPI are invalid Preamplifier resets are detected similarly Note Data acquisit...

Страница 39: ...devices introduce excessive noise temperature drift and significant non linearities into the signal In a significant departure from the previous design the updated blue microDXP design now employs a d...

Страница 40: ...in The Nominal Gain is independent of software control Its value is stored in non volatile memory accessible via the DSP parameters NOMGAIN UQ1 15 format unsigned mantissa and NOMGAINE exponent It is...

Страница 41: ...digitizes at either 40 MSPS default or 80 MSPS high speed option The ADC itself and passive components in the Nyquist filter are different in each case thus the clock speed cannot be increased via fir...

Страница 42: ...the previous design the microDXP now employs a switched gain amplifier architecture to offer up to 16 discrete analog gain settings i e gain that is applied to the analog signal before digitization S...

Страница 43: ...gy calibration is slightly off To first order the spectrum should remain calibrated but a slight shift in the pulse height measurement is not uncommon This is addressed by storing a unique Fine Gain T...

Страница 44: ...5 2 Serial Port SPORT The Analog Devices DSP synchronous serial port or SPORT supports a variety of serial data communications protocols and offers a maximum transfer rate of approximately 1Mbyte sec...

Страница 45: ...f other devices 3 6 3 I2C EEPROM The I2C serial EEPROM accessed by the PIC is used to store the DSP code and general system information The DSP is booted automatically upon power up The I2C memory can...

Страница 46: ...d on the microDXP The so called high speed interface includes all resources carried on the flex cable interface plus Direct Memory Access DMA to the DSP It was included for applications requiring very...

Страница 47: ...e requires a measurement of the voltage step Vx in the presence of the amplifier s noise Figure 4 1 and Figure 4 3 depict reset type and RC type charge sensitive amplifiers respectively In both figure...

Страница 48: ...rom successive x ray steps followed by the reset Note that the units here are Volts and milliseconds vs millivolts and microseconds in the previous figure Figure 4 2 The large signal reset waveform fo...

Страница 49: ...y applicable to RC type preamplifiers Figure 4 3 a RC type charge sensitive preamplifier with a positively biased detector b Output on absorption of an x ray Note that the step has a falling edge thus...

Страница 50: ...tep then the equation produces cusp like filters When the weighting values are constant one obtains triangular if the gap is zero or trapezoidal filters The concept behind cusp like filters is that si...

Страница 51: ...cally that if the noise in the signal is white i e Gaussian distributed above and below the step which is typically the case for the short shaping times used for high signal rate processing then the a...

Страница 52: ...s offering both triangular and semi Gaussian filtering by stretching the triangular peaking time a bit so that the true triangular peaking time is typically 1 2 times the selected semi Gaussian peakin...

Страница 53: ...tion e which is referred to as the electronic noise of the system a number which depends on the peaking time of the filter used Riding on top of this noise the x ray peaks contribute an additional noi...

Страница 54: ...the energy filter itself or a derivative of it is sampled periodically in the explicit absence of an x ray step defined by a baseline threshold In practice the DXP initially makes a series of NB base...

Страница 55: ...resolution at high rates The microDXP now employs a proprietary circuit that virtually eliminates this problem resulting in industry leading count rate stability 4 5 X ray Detection Setting Thresholds...

Страница 56: ...is usually trivial digitally then no system deadtime is produced by the capture and store operation This is a significant source of the enhanced throughput found in digital systems Once an active thre...

Страница 57: ...il in 4 7 Figure 4 7 In the default Peak Sensing mode the slow filter output is monitored and the peak value is selected This automatic mode typically yields the best performance In Peak Sampling mode...

Страница 58: ...LEN SLOWGAP X Equation 4 9 4 7 Pile up Inspection The captured value Vx see Figure 4 6 will only be a valid measure of its associated x ray s energy provided that the filtered pulse is sufficiently we...

Страница 59: ...ritically on the peaking time of the filter being used The amount of pileup which occurs at a given average signal rate will increase with longer peaking times We will quantify this in 4 9 where we di...

Страница 60: ...only a single though somewhat distorted pulse emerges from the slow filter but its peak amplitude corresponds to the energy of neither x ray 4 nor x ray 5 In order to reject as many of these fast chan...

Страница 61: ...as the OCR The DXP normally returns statistics in addition to the collected spectrum the REALTIME for which data was collected the triggering channel LIVETIME or sum of time during which the triggeri...

Страница 62: ...racking steps both of which incur additional dead time d 2 Peaking Time Gap Time Equation 4 15 The maximum value of OCR can be found by differentiating Equation 4 14 and setting the result to zero Thi...

Страница 63: ...microDXP excluding reset transients that may exceed the range for a few microseconds The input range is specified below in Table A 1 To accommodate preamplifiers with an output range in excess of 4V V...

Страница 64: ...nications as well as parallel IDMA access to DSP memory for transfer rates up to 10 Mbytes sec This parallel IDMA interface is used as the basis for the microCOMU USB interface The latest microDXP har...

Страница 65: ...nput connection J12 Flex Cable Port 30 conductor 0 5mm locking flex cable connector carries power communications and auxiliary digital I O Hirose P N FH12 30S 0 5SH e g flat flex cable Parlex P N 0 5M...

Страница 66: ...al port receive frame sync line ADSP218x SPORT Table A 5 Pin assignments for the 30 conductor flat flex interconnect J11 Board to Board Port 50 conductor 0 5mm mezzanine board to board receptacle carr...

Страница 67: ...signal conditioner Regulated 5 0V or unregulated 5 5V if on board regulator present 6 3 3VCC 3 3V DC supply for on board digital components 8 GND Internal ground connection 10 SPORT_RFS DSP serial por...

Страница 68: ...100mV pk pk from the switching supplies Voltage Range Current max Description 3 3V 150mV 200mA Decent switching supply 5 5V to 6 0V 30mA Linear or good switching supply 5 5V to 6 0V 30mA Linear or goo...

Страница 69: ...42 3 for details ID Parameter Description 0 NUMGENSET Number of GENSET parameters NOT including NUMGENSET and GENVERSION used internally 1 GENVERSION Version of the GENSET used internally 2 MCALEN Nu...

Страница 70: ...ternally 2 FASTLEN Fast filter ramp length 3 FASTGAP Fast filter gap 4 FSCALE Controls FiPPI fast filter scaling 5 MINWIDTH Minimum time above threshold for fast filter 6 MAXWIDTH Maximum time above t...

Страница 71: ...data bytes xor CS Exclusive or checksum bitwise xor of all bytes except for the initial Esc If the checksum is not correct an error response is returned Table E 1 RS 232 character definitions The for...

Страница 72: ...byte of the new RUNID 0x1B 27 0x18 bitwise XOR excludes escape character Response if unsuccessful 0x1B the escape character 0x00 the command is always returned 0x01 the low byte that sets the number...

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