Wide-dynamic range electrometer with a fast response
First Claim
1. An electrometer, comprising:
- an amplifier having an inverting input, a non-inverting input, and an output;
first and second resistive elements each having a first end and a second end, the first ends of the first and second resistive elements electrically coupled to the inverting input of the amplifier and the second end of the first resistive element electrically coupled to the output of the amplifier;
a buffer having a high-impedance input and an output, the second end of the second resistive element electrically coupled to the input of the buffer; and
at least one diode electrically coupling the output of the amplifier to the second end of the second resistive element,wherein the buffer is a second amplifier having an inverting input, a non-inverting input, and an output, the output of the second amplifier being electrically coupled to the inverting input of the second amplifier, the non-inverting input of the second amplifier being the input of the buffer and the output of the second amplifier being the output of the buffer.
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Abstract
A method and apparatus for measuring current includes sensing a first voltage at the output of an amplifier and computing a current based on the first voltage and the resistance of a first resistive element, which is electrically coupled between an inverting input of the amplifier and the output of the amplifier, if the first voltage is below a predetermined level. The method also includes sensing a second voltage at the output of a buffer and computing a current based on the first and second voltages and the resistances of the first resistive element and a second resistive element, which is electrically coupled between the inverting input of the amplifier and an input of the buffer and is also electrically coupled to the output of the amplifier through a at least one diode, if the voltage output from the amplifier is above the predetermined level.
67 Citations
12 Claims
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1. An electrometer, comprising:
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an amplifier having an inverting input, a non-inverting input, and an output; first and second resistive elements each having a first end and a second end, the first ends of the first and second resistive elements electrically coupled to the inverting input of the amplifier and the second end of the first resistive element electrically coupled to the output of the amplifier; a buffer having a high-impedance input and an output, the second end of the second resistive element electrically coupled to the input of the buffer; and at least one diode electrically coupling the output of the amplifier to the second end of the second resistive element, wherein the buffer is a second amplifier having an inverting input, a non-inverting input, and an output, the output of the second amplifier being electrically coupled to the inverting input of the second amplifier, the non-inverting input of the second amplifier being the input of the buffer and the output of the second amplifier being the output of the buffer. - View Dependent Claims (2, 3, 4, 5)
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6. An electrometer, comprising:
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an amplifier having an inverting input, a non-inverting input, and an output; first and second resistive elements each having a first end and a second end, the first ends of the first and second resistive elements electrically coupled to the inverting input of the amplifier and the second end of the first resistive element electrically coupled to the output of the amplifier; a buffer having a high-impedance input and an output, the second end of the second resistive element electrically coupled to the input of the buffer; at least one diode electrically coupling the output of the amplifier to the second end of the second resistive element, wherein the at least one diode comprises a first diode and a low-leakage and low-capacitance second diode having a first end and a second end, the first end of the second diode electrically coupled to the input of the buffer, the second end of the second diode electrically coupled to the first diode; a capacitor; and an adjustable gain amplifier having an input and an output, the input of the adjustable gain amplifier electrically coupled to the second end of the second diode, the output of the adjustable gain amplifier electrically coupled to the first end of the second diode through the capacitor, the adjustable gain amplifier being configured to discharge the capacitor with a charge opposite the charge in the second diode.
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7. An electrometer, comprising:
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an amplifier having an inverting input, a non-inverting input, and an output; first and second resistive elements each having a first end and a second end, the first ends of the first and second resistive elements electrically coupled to the inverting input of the amplifier and the second end of the first resistive element electrically coupled to the output of the amplifier; a buffer having a high-impedance input and an output, the second end of the second resistive element electrically coupled to the input of the buffer; at least one diode electrically coupling the output of the amplifier to the second end of the second resistive element; a first anti-alias filter and a second anti-alias filter, the first anti-alias filter electrically coupled to the output of the amplifier, the second anti-alias filter electrically coupled to the output of the buffer; and a first analog-to-digital (A/D) converter and a second A/D converter, the first A/D converter electrically coupled to the output of the first anti-alias filter, the second A/D converter electrically coupled to the output of the second anti-alias filter, the first A/D converter and the second A/D converter.
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8. A method for measuring current, comprising:
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sensing a first voltage at an output of an amplifier; computing a current based on the first voltage and a resistance of a first resistive element electrically coupled between an inverting input of the amplifier and the output of the amplifier if the first voltage is below a predetermined level; sensing a second voltage at the output of a buffer; computing a current based on the first and second voltages and the resistances of the first resistive element and a second resistive element, the second resistive element being electrically coupled between the inverting input of the amplifier and an input of the buffer, if the voltage output from the amplifier is above the predetermined level; sampling a change in forward voltage of at least one of a plurality of diodes electrically coupled between the input of the buffer and the output of the amplifier; and injecting a first charge into the at least one of the plurality of diodes, the first charge being opposite to a second charge associated with the at least one of the plurality of diodes. - View Dependent Claims (9)
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10. A method for measuring current, comprising:
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sensing a first voltage at an output of an amplifier; computing a current based on the first voltage and a resistance of a first resistive element electrically coupled between an inverting input of the amplifier and the output of the amplifier if the first voltage is below a predetermined level; sensing a second voltage at the output of a buffer; and computing a current based on the first and second voltages and the resistances of the first resistive element and a second resistive element, the second resistive element being electrically coupled between the inverting input of the amplifier and an input of the buffer, if the voltage output from the amplifier is above the predetermined level, wherein sensing the voltages comprises reading first voltage data output from a first A/D converter electrically coupled to the output of the amplifier and reading second voltage data output from a second A/D converter electrically coupled to the output of the buffer. - View Dependent Claims (11, 12)
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Specification