Pyroelectric sensor with high sensitivity

• US 4,868,390 A
• Filed: 02/16/1988
• Issued: 09/19/1989
• Est. Priority Date: 02/16/1988
• Status: Expired due to Fees

• Current Assignee: Eltec Instruments, Inc.
• Original Assignee: Eltec Instruments, Inc.
• Inventors: Villers, Fredrick, Keller, Hans J.
• Primary Examiner(s): Fields, Carolyn E.
• Assistant Examiner(s): HANIG, RICHARD E
• Application Number:
  US07/156,395
• Time in Patent Office: 581 Days
• Field of Search: 250/338.3, 250/349
• US Class Current: 250/338.3
• CPC Class Codes: G01J 5/34 using capacitors, e.g. pyroelectric capacitors

Abstract

A pyroelectric sensor circuit arrangement for reducing noise and increasing sensitivity has a main current amplifier with a high feedback resistor connected to receive input from an electrode of a pyroelectric element, and includes a compensation amplifier in a unity gain amplifier configuration connected to a common power source with the main amplifier. The compensation amplifier is connected to discharge transients from the pyroelectric element when electrode voltage exceeds the positive voltage or goes below the negative voltage of the power source. A pair of anti-parallel diode or similar component is connected between the main amplifier input and the compensation amplifier output.

Claims

1. A pyroelectric sensor element having a high sensitivity to radiation and a low noise output signal, comprising:

a power source having positive and negative terminals;

a pyroelectric element having a piece of pyroelectric material connected between two electrodes to develop an electrical signal across said electrodes responsive to radiation incident on said material;

a current amplifier in the form of a first operational amplifier connected to said power source and having a first input terminal connected directly to one of said electrodes, a second input terminal for receiving a reference voltage signal, and an output terminal;

said current amplifier including a feedback resistor connected between said output terminal and said first input terminal of high resistance so that amplifier noise is negligible;

a compensation amplifier in the form of a second operational amplifier connected to said power source and having a first input terminal connected directly to said one electrode, and an output terminal; and

discrete circuit component means connected directly between said output terminal of said compensation amplifier and said first input terminal of said first operational amplifier, said compensation amplifier being operational and said component means functioning to inhibit input current noise to said current amplifier for protecting said current amplifier from overloading when the voltage of said electrode exceeds the voltage of said positive terminal or falls below the voltage of said negative terminal by acting to maintain the voltage at said first input terminal of said current amplifier at substantially the same voltage as the voltage at said output terminal of said compensation amplifier, with minimum voltage drop across said component means and minimum noise-generating current flow therethrough.

2. A sensor as in claim 1, wherein said second operational amplifier further comprises a second input terminal connected to its output terminal in the form of a unity gain amplifier.

3. A sensor as in claim 2, wherein said discrete component element means comprises oppositely directed diodes connected in parallel between said output terminal of said compensation amplifier and said first input terminal of said current amplifier.

4. A sensor as in claim 2, wherein said circuit element means comprises a resistor connected between said output terminal of said compensation amplifier and said first input terminal of said current amplifier.

5. A sensor as in claim 1, further comprising a second pyroelectric element connected in series with said first pyroelectric element.

6. A sensor as in claim 1, further comprising a second pyroelectric element connected in parallel with said first pyroelectric element.

7. A sensor as in claim 2, further comprising a second pyroelectric element connected in series with said first pyroelectric element.

8. A sensor as in claim 2, further comprising a second pyroelectric element connected in parallel with said first pyroelectric element.

9. A sensor as in claim 3, further comprising a second pyroelectric element connected in series with said first pyroelectric element.

10. A sensor as in claim 3, further comprising a second pyroelectric element connected in parallel with said first pyroelectric element.

11. A sensor as in claim 4, further comprising a second pyroelectric element connected in series with said first pyroelectric element.

12. A sensor as in claim 4, further comprising a second pyroelectric element connected in parallel with said first pyroelectric element.