Low noise, electric field sensor

• US 20040070446A1
• Filed: 08/14/2003
• Published: 04/15/2004
• Est. Priority Date: 02/13/2001
• Status: Active Grant

• Current Assignee: Quantum Applied Science And Research, Inc.
• Original Assignee: Quantum Applied Science And Research, Inc.
• Inventors: Krupka, Michael Andrew
• Granted Patent: US 7,088,175 B2
• Time in Patent Office: Days
• US Class Current: 330/69
• CPC Class Codes: G01R 29/0871 Complete apparatus or systems; circuits, e.g. receivers or amplifiers G01R29/0878, G01R29/0892 take precedence; dosimeters, warning devices G01R29/0857
• 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 1/26 Modifications of amplifiers to reduce influence of noise generated by amplifying elements
• CPC Class Codes: H03F 1/30 Modifications of amplifiers to reduce influence of variations of temperature or supply voltage or other physical parameters in differential amplifiers H03F3/45479
• 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 1/56 Modifications of input or output impedances, not otherwise provided for
• CPC Class Codes: H03F 2200/153 Feedback used to stabilise the amplifier
• CPC Class Codes: H03F 2200/261 Amplifier which being suitable for instrumentation applications

Abstract

A system for measuring a free space electric field includes an ultrahigh impedance antenna positioned in the electric field to generate a signal from the electric field. An amplifier having an input port is provided to amplify the signal. The amplifier generates an input bias current which combines with the signal to create an input potential at the input port. An electrical circuit connects the input port to a ground connection and includes at least one circuit element for controlling the input potential to stabilize the signal at the input port.

Claims

1. A system for measuring a free space electric field, said system comprising:

a ground connection;

an ultrahigh impedance antenna positioned in the electric field for generating a signal from the electric field;

an amplifier having an input port, wherein said amplifier generates an input bias current, said input bias current being combined with the signal to create an input potential at the input port; and

an electrical circuit connected to said input port and said ground connection, said electrical circuit having at least one circuit element for controlling said input potential to stabilize said signal at said input port.

2. A system as recited in claim 1 wherein said circuit element is a resistor having a resistance in the range of 10 to 10,000 GΩ

.

3. A system as recited in claim 1 wherein said electrical circuit establishes a feedback path for said amplifier.

7. A system as recited in claim 1 wherein said amplifier has an input capacitance and said system further comprises a means for eliminating the effect of said input capacitance of said amplifier.

8. A system as recited in claim 7 wherein said eliminating means comprises a capacitor.

9. A system as recited in claim 8 wherein said eliminating means further comprises an amplifier having a gain of two.

10. A system as recited in claim 1 wherein said amplifier is selected from the group of amplifiers consisting of an operational amplifier, an instrumentation amplifier and a transistor.

4. A system as recited in claim 4 wherein said electrical circuit comprises a means for generating negative feedback for said amplifier below a selected cutoff frequency.

5. A system as recited in claim 4 wherein said electrical circuit comprises a means for generating high gain negative feedback for said amplifier below a selected cutoff frequency and substantially no feedback above said selected cutoff frequency.

6. A system as recited in claim 4 wherein said electrical circuit comprises a means for generating a high gain negative feedback for said amplifier below a first selected cutoff frequency ν

₁, a high gain negative feedback for said amplifier above a second selected cutoff frequency ν

₂, and substantially no feedback at frequencies between ν

₁ and ν

₂.

11. A system for measuring a free space electric field, said system comprising:

a ground connection;

an antenna positioned in the electric field for generating a substantially a.c. signal from the electric field;

an amplifier having an input port, wherein said amplifier generates a substantially d.c. input bias current, said d.c. input bias current being combined with the a.c. signal to create an input potential at the input port; and

an electrical circuit connected to said input port and said ground connection, said electrical circuit having at least one circuit element for draining said d.c. input potential to said ground connection to stabilize said a.c. signal at said input port.

12. A system as recited in claim 11 wherein said circuit element is a resistor having a resistance in the range of 10 to 10,000 GΩ

.

13. A system as recited in claim 11 wherein said electrical circuit establishes a feedback path for said amplifier.

14. A system as recited in claim 13 wherein said electrical circuit comprises a means for generating negative feedback for said amplifier below a selected cutoff frequency.

15. A system as recited in claim 11 wherein said amplifier has an input capacitance and said system further comprises a means for eliminating the effect of said input capacitance of said amplifier.

16. A method for measuring a free space electric field, said method comprising the steps of:

positioning an ultrahigh impedance antenna in the electric field to generate a signal from the electric field;

connecting said antenna to an input port of an amplifier, wherein said amplifier generates an input bias current, said input bias current being combined with the signal to create an input potential at the input port; and

connecting an electrical circuit to said input port and to a ground connection, said electrical circuit having at least one circuit element for controlling said input potential to stabilize said signal at said input port.

17. A method as recited in claim 16 wherein said circuit element is a resistor having a resistance in the range of 10 to 10,000 GΩ

.

18. A method as recited in claim 16 wherein said electrical circuit establishes a feedback path for said amplifier.