AN AMPLIFIER

• US 20200136569A1
• Filed: 11/10/2017
• Published: 04/30/2020
• Est. Priority Date: 03/16/2017
• Status: Active Grant

• Current Assignee: Isotopx, Ltd.
• Original Assignee: Isotopx, Ltd.
• Inventors: Volkovoy, Vadim, Jones, Anthony Michael, Tootell, Damian Paul
• Granted Patent: US 11,232,937 B2
• Time in Patent Office: Days
• CPC Class Codes: G01T 1/17 Circuit arrangements not adapted to a particular type of detector pulse-selection circuits H03K, G01R
• CPC Class Codes: G01T 7/005 calibration techniques stabilization of spectrometer G01T1/40
• CPC Class Codes: H01J 49/025 Detectors specially adapted to particle spectrometers data acquisition H01J49/0036; detectors per se G01T, e.g. G01T1/28, G01T1/29
• CPC Class Codes: H03F 1/08 Modifications of amplifiers to reduce detrimental influences of internal impedances of amplifying elements wide-band amplifiers with inter-stage coupling networks incorporating these impedances H03F1/42
• CPC Class Codes: H03F 1/303 using a switching device H03F1/305, H03F3/005, H03F3/38 take precedence
• CPC Class Codes: H03F 1/34 Negative-feedback-circuit arrangements with or without positive feedback H03F1/02 - H03F1/30, H03F1/38 - H03F1/50, H03F3/50 take precedence ; for rejection of common mode signals H03F3/45479
• CPC Class Codes: H03F 2200/126 A diode being coupled in a feedback path of an amplifier stage, e.g. active or passive diode
• CPC Class Codes: H03F 2200/129 there being a feedback over the complete amplifier
• CPC Class Codes: H03F 2200/321 Use of a microprocessor in an amplifier circuit or its control circuit
• CPC Class Codes: H03F 2200/471 the voltage being sensed
• CPC Class Codes: H03F 2203/45116 Feedback coupled to the input of the differential amplifier
• CPC Class Codes: H03F 2203/45512 the FBC comprising one or more capacitors, not being switched capacitors, and being coupled between the LC and the IC
• CPC Class Codes: H03F 2203/45536 the FBC comprising a switch and being coupled between the LC and the IC
• CPC Class Codes: H03F 3/45071 with semiconductor devices only
• CPC Class Codes: H03F 3/45475 using IC blocks as the active amplifying circuit
• CPC Class Codes: H03F 3/70 Charge amplifiers

Abstract

A capacitive trans-impedance amplifier comprising a voltage amplifier having an inverting input terminal for connection to an input current source. A feed-back capacitor is coupled between the inverting input terminal and the output terminal to accumulate charges received from the input current source and to generate a feed-back voltage accordingly. A calibration unit includes a calibration capacitor electrically coupled, via a calibration switch, to the inverting input terminal and electrically coupled to the feed-back capacitor. The calibration unit is operable to switch the calibration switch to a calibration state permitting a discharge of a quantity of charge from the calibration capacitor to the feed-back capacitor. The capacitive trans-impedance amplifier is arranged to determine a voltage generated across the feed-back capacitor while the calibration switch is in the calibration state and to determine a capacitance value (C=Q/V) for the feed-back capacitor according to the value of the generated voltage (V) and the quantity of charge (Q).

Claims

1. A capacitive trans-impedance amplifier comprising:

a voltage amplifier having an inverting input terminal for connection to an input current source, and a non-inverting input terminal, the voltage amplifier being arranged to provide at an output terminal thereof an output voltage signal;

a feed-back capacitor coupled between the inverting input terminal and the output terminal to accumulate charges received from the input current source and to generate a feed-back voltage accordingly wherein the capacitor defines a negative feed-back loop of the voltage amplifier such that the output voltage is proportional to said accumulation of said charges;

a calibration unit including a calibration capacitor electrically coupled, via a calibration switch, to said inverting input terminal of said voltage amplifier and thereby electrically coupled to said feed-back capacitor, wherein the calibration unit is operable to switch the calibration switch to a calibration state permitting a discharge of a quantity of charge from the calibration capacitor to the feed-back capacitor,

wherein the capacitive trans-impedance amplifier is arranged to determine a voltage generated across said feed-back capacitor while said calibration switch is in said calibration state and to determine a capacitance value (C=Q/V) for the feed-back capacitor according to the value of the generated voltage (V) and the quantity of charge (Q).

2. A capacitive trans-impedance amplifier according to claim 1 in which said calibration switch comprises a photodiode operable to attain said calibration state in responsive to receipt of optical radiation sufficient to render the photodiode conductive.

3. A capacitive trans-impedance amplifier according to claim 1 including a reset switch electrically coupled to the inverting input terminal of the voltage amplifier and electrically isolated from the output terminal of the voltage amplifier, wherein the switch is switchable to a state permitting a transfer of charge from the feedback capacitor or to the feedback capacitor.

4. A capacitive trans-impedance amplifier according to claim 3 in which the reset switch is switchable to a state permitting a discharge of at least some of said accumulated charge from said feed-back capacitor.

5. A capacitive trans-impedance amplifier according claim 3 in which the reset switch comprises a semiconductor device switchable to generate at a terminal thereof, which is electrically coupled to said inverting input, an electrical charge having a polarity opposite to that of said accumulated charge, thereby permitting said discharge of accumulated charge to neutralise said electrical charge generated by the reset switch.

6. A capacitive trans-impedance amplifier according to claim 4, including a controller unit arranged to monitor a voltage across said feed-back capacitor acquired from said accumulated charge, and to control said reset switch to permit said discharge of accumulated charge when the acquired voltage rises above a first threshold voltage value which lies within the dynamic range of the voltage amplifier.

7. A capacitive trans-impedance amplifier according to claim 6 in which the reset switch is switchable between a first state permitting said discharge of accumulated charge and a second state which does not permit said discharge of accumulated charge, wherein the controller unit is arranged to monitor a voltage across said feed-back capacitor while said switch is in said first state, and to control said reset switch to achieve said second state when the monitored voltage falls below a second threshold voltage value which lies within the dynamic range of the voltage amplifier.

8. A capacitive trans-impedance amplifier according to claim 1 including an analyser unit arranged to determine a rate of change of voltage across the feed-back capacitor resulting from said accumulation of charge, and to generate a current value representing a current received by the capacitive trans-impedance amplifier from a said input current source.

9. A capacitive trans-impedance amplifier according to claim 1 in which the voltage amplifier comprises an operational amplifier.

10. A capacitive trans-impedance amplifier according to claim 1 in which said reset switch comprises a diode.

11. A capacitive trans-impedance amplifier according to claim 1 in which said calibration switch comprises a diode.

12. A capacitive trans-impedance amplifier according to claim 1 comprising a cooler apparatus/unit arranged to cool the voltage amplifier to a temperature falling between 0 (zero) degrees Celsius and −

50 degrees Celsius to reduce thermal noise in the voltage amplifier.

15. A mass spectrometer comprising an ion beam current measurement device comprising a capacitive trans-impedance amplifier according to claim 1.

13. (canceled)

14. (canceled)

16. (canceled)

17. (canceled)

18. A method of capacitive trans-impedance amplification comprising:

providing a voltage amplifier having an inverting input terminal electrically coupled to an input current source, and a non-inverting input terminal, the voltage amplifier being arranged to provide an output voltage signal at an output terminal thereof;

providing a feed-back capacitor coupled between the inverting input terminal and the output terminal to accumulate charges received from the input current source and to generate a feed-back voltage accordingly wherein the capacitor defines a negative feed-back loop of the voltage amplifier such that the output voltage is proportional to said accumulation of said charges;

providing a calibration unit including a calibration capacitor electrically coupled, via a calibration switch, to said inverting input terminal of said voltage amplifier and thereby electrically coupled to said feed-back capacitor,

switching, by the calibration unit, the calibration switch to a calibration state permitting a discharge of a predetermined charge from the calibration capacitor to the feed-back capacitor,

determining a voltage generated across said feed-back capacitor while said calibration switch is in said calibration state; and

determining a capacitance value (C=Q/V) for the feed-back capacitor according to the value of the generated voltage (V) and the predetermined charge (Q).

19. A method according to claim 18 including;

providing a reset switch electrically coupled to the inverting input terminal of the voltage amplifier and electrically isolated from the output terminal of the voltage amplifier;

using the feed-back capacitor to accumulate charges received from the input current source and generating said output voltage accordingly such that the output voltage is proportional to said accumulation of said charges; and

,

switching the reset switch to a state permitting a transfer of charge from the capacitor or to the capacitor.

20. A method according to claim 19 including switching the reset switch to a state permitting a discharge of at least some of said accumulated charge from said feed-back capacitor.

21. A method according to claim 19 in which the reset switch comprises a semiconductor device and the method includes switching the reset switch to generate at a terminal thereof, which is electrically coupled to said inverting input, an electrical charge having a polarity opposite to that of said accumulated charge, thereby permitting said discharge of accumulated charge to neutralise said electrical charge generated by the reset switch.

22. A method according to claim 19, including monitoring a voltage across said feed-back capacitor acquired from said accumulated charge, and controlling said reset switch to permit said discharge of accumulated charge when the acquired voltage rises above a first threshold voltage value which lies within the dynamic range of the voltage amplifier.

23. A method according to claim 22 including switching the reset switch between a first state permitting said discharge of accumulated charge and a second state which does not permit said discharge of accumulated charge, wherein the method includes monitoring a voltage across said feed-back capacitor while said reset switch is in said first state, and to controlling said reset switch to achieve said second state when the monitored voltage falls below a second threshold voltage value which lies within the dynamic range of the voltage amplifier.

24. A method according to claim 18 including determining a rate of change of voltage across the feed-back capacitor resulting from said accumulation of charge, and generating a current value representing a current received by the feed-back capacitor from said input current source.

25. (canceled)

26. (canceled)