WO2008060670A2 - Dispositif de conversion de tension en fréquence à faible bruit et procédé de mesure de quanta - Google Patents

Dispositif de conversion de tension en fréquence à faible bruit et procédé de mesure de quanta Download PDF

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Publication number
WO2008060670A2
WO2008060670A2 PCT/US2007/067108 US2007067108W WO2008060670A2 WO 2008060670 A2 WO2008060670 A2 WO 2008060670A2 US 2007067108 W US2007067108 W US 2007067108W WO 2008060670 A2 WO2008060670 A2 WO 2008060670A2
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WO
WIPO (PCT)
Prior art keywords
sampling period
pulses
fractional
circuitry
representative
Prior art date
Application number
PCT/US2007/067108
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English (en)
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WO2008060670A3 (fr
Inventor
David Rohler
Original Assignee
Multi-Dimensional Imaging, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by Multi-Dimensional Imaging, Inc. filed Critical Multi-Dimensional Imaging, Inc.
Publication of WO2008060670A2 publication Critical patent/WO2008060670A2/fr
Publication of WO2008060670A3 publication Critical patent/WO2008060670A3/fr

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Classifications

    • G—PHYSICS
    • G04—HOROLOGY
    • G04F—TIME-INTERVAL MEASURING
    • G04F10/00—Apparatus for measuring unknown time intervals by electric means
    • G04F10/005—Time-to-digital converters [TDC]
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M1/00—Analogue/digital conversion; Digital/analogue conversion
    • H03M1/12—Analogue/digital converters
    • H03M1/14—Conversion in steps with each step involving the same or a different conversion means and delivering more than one bit
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M1/00—Analogue/digital conversion; Digital/analogue conversion
    • H03M1/12—Analogue/digital converters
    • H03M1/60—Analogue/digital converters with intermediate conversion to frequency of pulses

Definitions

  • the present invention relates generally to voltage-to-frequency (VFC) converters and, more particularly, to a voltage-to-frequency conversion device and method that uses information before a first pulse of a sample period and information after a last pulse of a sample period to determine the number of pulses during a sample period.
  • VFC voltage-to-frequency
  • VFC Voltage-to-frequency converters
  • VFC Voltage-to-frequency converters
  • IFC current-to-frequency converters
  • the VFC is often used in applications involving the measurement of some type of flux density, for example, the detection of x-ray intensity. In such applications, there is a quantum noise component, based on the physics of flux measurement.
  • a disadvantage of the conventional VFC, in this type of application, is that the measured noise is higher in regions of low flux intensity than the quantum noise.
  • the present invention provides a voltage-to-frequency conversion (VFC) device and method that determines the flux density of energy during a sample period based on information before a first pulse of the sample period and information after a last pulse of the sample period to determine the number of pulses during a sample period.
  • VFC voltage-to-frequency conversion
  • the VFC device is configured to avoid problems associated with higher measured noise in regions of low flux density.
  • One aspect of the invention relates to a voltage-to-frequency method and/or device wherein information before the first pulse of a sample period and/or information after the last pulse of a/the sample period is used in determining the number of pulses in the sample period
  • One aspect of the invention relates to a voltage-to-frequency conversion (VFC) device that includes circuitry that generates pulses in response to received energy, the pulses being indicative of receipt of a predetermined amount of received energy; circuitry that determines a number of whole pulses within a sampling period; circuitry that determines a number of fractional pulses within the sampling period; and circuitry that calculates and outputs a final energy value signal based on the number of whole and fractional pulses during the sampling period, the final energy value being indicative of total received energy during the sampling period.
  • VFC voltage-to-frequency conversion
  • the circuitry that determines a number of fractional pulses determines if there are any fractional pulses occurring at a beginning of the sampling period and if there are any fractional pulses occurring at an end of the sampling period.
  • Another aspect of the invention relates to a method of determining total flux density of energy received during a sampling period. The method includes generating pulses in response to the received energy, the pulses being indicative of receipt of a predetermined quantity of received energy; determining a number of whole pulses within the sampling period; determining a number of fractional pulses within or adjacent the sampling period; and outputting a final value signal indicative of total flux density of energy received during the sampling period, the final value being determined based on the number of whole and fractional pulses within or adjacent the sampling period.
  • Another aspect of the invention relates to a method of converting received energy into a digital signal representative of the received energy.
  • the method includes generating digital pulses in response to a received analog signal representative of the received energy, the digital pulses being indicative of receipt of a predetermined quantity of received energy; setting a sampling period; counting a number of whole pulses within the sampling period; determining a number of fractional pulses within the sampling period; outputting a digital value representative of total flux density of energy received during the sampling period, the digital valued being determined based on the number of whole and fractional pulses within the sampling period.
  • Another aspect of the invention relates to a radiation detection circuit for use with a radiation detector.
  • the radiation detector circuit includes circuitry that generates digital pulses in response to an analog signal representative of received energy, the pulses being indicative of receipt of a predetermined flux of received energy; and circuitry that transforms the digital pulses into an output signal representative of total flux received during a sampling period based on number of whole pulses and number of fractional pulses within the sampling period.
  • FIG. 1 is a diagrammatic illustration of a voltage-to-frequency conversion (VFC) device in accordance with one aspect of the invention
  • FIG. 2 is an exemplary pulse sequence diagram used to illustrate aspects of the VFC device
  • FIG. 3 is an exemplary plot of pulse numbers and time as a function of x-ray photons per second
  • FIG. 4 is a diagrammatic illustration of a counting circuitry portion of the VFC device in accordance with an aspect of the invention.
  • FIG. 5 is a diagrammatic illustration of a digital processing circuitry portion of the VFC device in accordance with an aspect of the invention
  • FIG. 6 is a plot of noise ratio between the inventive VFC device and a conventional VFC device as a function of x-ray photons per second;
  • FIG. 7 is a plot of noise amplitude as a function of x-ray photons per second comparing the inventive VFC device to a conventional VFC device; and FIG. 8 includes images corresponding to computed tomography scan simulations comparing the inventive VFC device to a conventional VFC device.
  • VFC voltage-to-frequency conversion
  • IFC current-to-frequency conversion
  • the VFC device and method will be described in connection with the exemplary application of use in connection with a data acquisition system used to measure flux density, e.g., in connection with a radiation detector for the detection of x-ray intensity.
  • the analog input to the VFC is a signal that is (generally) proportional to flux/unit time.
  • VFC voltage-to-frequency conversion
  • the VFC device 10 is configured to receive an input signal 12 indicative of received energy, e.g., received flux density from an associated radiation detector, such as an x- ray detector, by appropriate analog circuitry 14 (also referred to as an analog stage).
  • An analog offset signal 16 also is received by the analog circuitry.
  • the input signal indicative of flux density 12 is constantly integrated.
  • the analog stage or analog circuitry 14 of the VFC device may be implemented using a variety of configurations and/or circuit or software implementation, including, for example, the implementation(s) described in "Analog-to-Digital Conversion Techniques With COPSTM Family Microcontrollers", National Semiconductor, COP Note 1 , Leonard A. Distaso, February, 1980, which is incorporated herein by reference in its entirety.
  • the VFC device 10 includes digital counting circuitry 20, (also referred to as a digital counting stage), which receives pulses 18 from the analog circuitry 14 along with a high-frequency clock signal and sample trigger signal. In the digital counting stage 20, the numbers of pulses from the analog circuitry that occur within a specified sample period are counted. Also, depending on the particular implementation of the VFC device and/or method, timing values may be determined by counting clock pulses.
  • the digital counting circuitry 20 outputs digital counting values 22 (along with other values to be used in later stages) to digital processing circuitry 24 (also referred to as a digital processing stage).
  • digital processing circuitry 24 also referred to as a digital processing stage.
  • a final digital output value which is representative of the flux accumulated during the sample period, is determined.
  • the VFC device and method provide for determination of the digital value of accumulated flux by identification and counting of the number of whole pulses occurring during the sampling period as well as any fractional pulses occurring at the beginning and/or end of the sampling period.
  • an exemplary digital pulse train 30, e.g., a digital pulse train generated by the analog circuitry 14 portion of the VFC device, is provided for purposes of illustrating the VFC device and method described herein.
  • the exemplary digital pulse train 30 is indicated in relation to an exemplary sample period (S) 32.
  • S sample period
  • the symbol i is an index for the sample number.
  • P number of pulse durations inside the sample period
  • P 1 P 1 -I time between the first and last pulses in units of clock ticks
  • the digital value, Vj, representative of the total flux for a sampling period is obtained according to Equation 1 :
  • This conventional VFC device and method simply takes the ratio of the number of whole or complete pulse durations, Pi, during the time between the first and last pulses in units of clock ticks, Tj, minus a predetermined digital offset value Op. While the numerical accuracy of this computation is relatively high (because the "T value” provides the "fractional part” of the pulse count), it can be seen in the graph in FIG. 3 that the variation in T is important for small values of P. However, it will be noted that the signal is integrated only for the fraction of the sampling period corresponding to TJS. This results in a corresponding loss of flux and, therefore, higher noise. It will be appreciated that the actual noise depends on certain parameters of the data acquisition. Table 2 provides a list of exemplary parameters and exemplary values that might be used, e.g., in a computed tomography (CT) data acquisition system.
  • CT computed tomography
  • FIG. 4 provides a diagrammatic illustration of a portion of the counting circuitry portion 20 (also referred to as the digital counting stage) of the VFC device 10
  • FIG. 5 provides a diagrammatic illustration of a preferred embodiment of digital processing circuitry portion 22 of the VFC device 10.
  • the analog circuitry 14 receives signals 12 indicative or otherwise representative of flux density, and converts these signals 12 into a digital pulse train 18.
  • the digital pulse train 18 is input into the digital counting circuitry 20, which is driven by an appropriate clock signal 34, e.g., a high-frequency clock signal, and an appropriate sample period trigger signal 36.
  • the digital counting circuitry 20 processes the digital pulse train 18 and outputs, for each sample period, signals 22 representative of the number of whole pulses, P, per sampling period, representative of the clock tick within the sample period / corresponding to the first pulse (in the range [0, S-1]), Aj, and representative of the clock tick within the sample period / corresponding to the last pulse (in the range [0, S-1]), Bj.
  • the VFC device 10 (and associated method) utilizes the A and S values, shown in FIG. 2, instead of the difference, T, between A and B as with the conventional VFC device. Specifically, the digital processing circuitry 24 of the VFC device 10 computes a digital value, V, as follows:
  • Equation 2 the first term, Pj, represents the "whole" number of pulses occurring in the sample period. The remaining terms represent the fraction of
  • the VFC device 10 is configured to process the information before the first pulse and after the last pulse, whereas the conventional VFC device does not include this information in its determination of the total number of pulses within the sample period.
  • the number of pulses in the sample period is large, that is, when ' , this loss of information is negligible.
  • T ' ⁇ S the loss of information in the conventional VFC device and method may be significant.
  • FIG. 6 illustrates the noise amplitude of a conventional VFC device and method compared to the quantum noise from the invention VFC device and method described herein.
  • FIG. 5 one exemplary embodiment of the digital processing circuitry 24 is illustrated. In the following description of FIG.
  • the block diagram shown in FIG. 5 diagrammatically illustrates one embodiment of the digital implementation of Equation 2 above. It should be noted that, since the variable, S, in Equation 2 is a constant, it is not required to incorporate the divide by S into the implementation.
  • the digital processing circuitry 24 includes circuitry 40 to determine a number of whole pulses within a sampling period and circuitry 42 that determines a number of fractional pulses within the sampling period. It will be appreciated that a variety of circuit and/or software configurations may be employed to accomplish adding functionality (designated generally by adders 46), inverting functionality (designated generally by inverters 48), multiplying functionality (designated generally by multipliers 50), and subtraction functionality (designated generally by subtractor 52). In essence, the digital processing circuitry is configured to calculate and output a final digital value, V 1 , which is indicative or otherwise representative of total energy flux accumulated during the sampling period, based on the number of whole and fractional pulses during the sampling period.
  • V 1 final digital value
  • the analog stage 14 of the VFC device 10 can operate with a smaller analog offset value 16; that is, with the VFC device the analog offset value, O A , can be set at approximately half the amplitude as compared to that of the conventional VFC device. This results in an approximately 2X increase in analog dynamic range in comparison to the conventional VFC device.
  • the measured digital values for one or more sequential periods are:
  • the digital processing stage 24 would be configured so that there is an output buffer with some reasonable length, e.g., N.
  • the offset value would be set so that there would be at least one pulse within N sample periods.
  • the digital processing stage would detect that a sample period had no pulse and alter its computation so that for each of the M ⁇ N successive periods with no pulse,
  • Equation 3 In these very low signal areas, this capability has provided a way to further improve the analog dynamic range. It should be noted, however, that whenever this state occurs, the data is effectively being filtered (smoothed). In fact, this dynamic filtering capability can be construed as a significant advantage in that the smoothing only occurs when the signal amplitude is very low and the signal-to-noise ratio is also low.
  • FIG. 8 provides a computed tomography (CT) scan simulation that compares the performance of the herein described VFC device with a conventional VFC device.
  • CT computed tomography
  • VFC device (and the functionality associated with the VFC device) may be carried out in a variety of ways, including, but not limited to, dedicated hardware, firmware, software or combinations thereof without departing from the scope of the present invention.

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  • Engineering & Computer Science (AREA)
  • Theoretical Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Analogue/Digital Conversion (AREA)
  • Measuring Frequencies, Analyzing Spectra (AREA)

Abstract

L'invention concerne un dispositif de conversion de tension en fréquence (VFC) comportant une circuiterie produisant des impulsions en réponse à de l'énergie reçue, une circuiterie déterminant un nombre entier d'impulsions dans une période d'échantillonnage, et une circuiterie déterminant des impulsions fractionnelles dans la période d'échantillonnage. Le dispositif de conversion de tension en fréquence est conçu pour émettre une valeur numérique caractéristique d'une densité de flux totale accumulée au cours de la période d'échantillonnage sur la base des impulsions entières et des impulsions fractionnelles dans la période d'échantillonnage.
PCT/US2007/067108 2006-04-20 2007-04-20 Dispositif de conversion de tension en fréquence à faible bruit et procédé de mesure de quanta WO2008060670A2 (fr)

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US60/745,221 2006-04-20

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2478272A (en) * 2010-01-15 2011-09-07 Jevon Raymond Davies A low noise analogue to digital converter using a set of parallel current to frequency converters
CN102820881A (zh) * 2012-08-06 2012-12-12 深圳市汇川技术股份有限公司 模拟电压输入电路及方法
FR2997496A1 (fr) * 2012-10-25 2014-05-02 St Microelectronics Grenoble 2 Detection de niveau de luminosite ambiante

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20020141530A1 (en) * 2000-11-14 2002-10-03 Marconi Medical Systems, Inc. Data acquisition for computed tomography
WO2004100792A1 (fr) * 2003-05-14 2004-11-25 Koninklijke Philips Electronics N.V. Procede et appareil destines a ameliorer la detection de rayonnements
WO2005121988A2 (fr) * 2004-06-04 2005-12-22 Warburton William K Procede et dispositif permettant d'ameliorer les limites de detection sur des systemes de spectroscopie en rayons x et nucleaire

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20020141530A1 (en) * 2000-11-14 2002-10-03 Marconi Medical Systems, Inc. Data acquisition for computed tomography
WO2004100792A1 (fr) * 2003-05-14 2004-11-25 Koninklijke Philips Electronics N.V. Procede et appareil destines a ameliorer la detection de rayonnements
WO2005121988A2 (fr) * 2004-06-04 2005-12-22 Warburton William K Procede et dispositif permettant d'ameliorer les limites de detection sur des systemes de spectroscopie en rayons x et nucleaire

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2478272A (en) * 2010-01-15 2011-09-07 Jevon Raymond Davies A low noise analogue to digital converter using a set of parallel current to frequency converters
CN102820881A (zh) * 2012-08-06 2012-12-12 深圳市汇川技术股份有限公司 模拟电压输入电路及方法
FR2997496A1 (fr) * 2012-10-25 2014-05-02 St Microelectronics Grenoble 2 Detection de niveau de luminosite ambiante
US9074939B2 (en) 2012-10-25 2015-07-07 Stmicroelectronics (Grenoble 2) Sas Ambient luminosity level detection based on discharge times
US9927291B2 (en) 2012-10-25 2018-03-27 Stmicroelectronics (Grenoble 2) Sas Ambient luminosity level detection
US11029200B2 (en) 2012-10-25 2021-06-08 Stmicroelectronics (Grenoble 2) Sas Ambient luminosity level detection

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