Shielded amplifier

• US 4,454,481 A
• Filed: 03/04/1982
• Issued: 06/12/1984
• Est. Priority Date: 03/04/1982
• Status: Expired due to Term

• Current Assignee: Conexant Systems Incorporated (Synaptics Incorporated)
• Original Assignee: Rockwell International Corporation
• Inventors: Lewis, Harold F.
• Primary Examiner(s): Mullins, James B.
• Assistant Examiner(s): Wan, Gene
• Application Number:
  US06/354,840
• Time in Patent Office: 831 Days
• Field of Search: 330/307, 330/207 R, 357/51, 357/84, 307/302
• US Class Current: 330/307
• CPC Class Codes: H03F 1/083 in transistor amplifiers H03F1/10 - H03F1/22 take precedence
• CPC Class Codes: H03F 1/42 Modifications of amplifiers to extend the bandwidth
• CPC Class Codes: H05K 9/0039 Galvanic coupling of ground layer on printed circuit board [PCB] to conductive casing printed shielding conductors, ground planes or power planes for reduction of cross-talk or noise in printed circuits H05K1/0218

Abstract

A shielded amplifier adapted for use with an infrared detector array mounted on a focal plane and operating in a cryogenically cooled environment and adapted to receive a signal output from a high impedance signal source, the shielded amplifier being required to amplify the signal with relatively uniform gain over a predetermined bandwidth comprising a base substrate of semiconductor material, an integrated amplifier circuit means formed on the base substrate, a resistor connected for negative feedback between the output terminal and the input terminal, a conductive shield interposed between the resistor and the integrated amplifier circuit means, a first insulating means for insulating the resistor from the conductive shield, a second insulating means for insulating the conductive shield from the integrated circuit amplifier means; whereby the conductive shield is disposed to reduce stray parasitic capacitance thereby increasing the shielded amplifier uniform gain over a predetermined bandwidth.

Claims

1. A shielded amplifier adapted for connection to a power source and having an input terminal and output terminal and being referenced to a reference potential, said shielded amplifier being further adapted to receive a signal from a high impedance signal source referenced to said reference potential, said shielded amplifier being required to amplify said signal with relatively uniform gain over a predetermined bandwidth and to output said amplified signal at said output terminal and wherein said bandwidth is subject to substantial degradation due to stray parasitic capacitance, said shielded amplifier comprising:

a substantially planar base substrate of semiconductor material having a first surface, said input and output terminals being formed on said first surface;

an integrated amplifier circuit means formed on said first surface, for amplifying said signal present at said input terminal and to provide an amplified signal to said output terminal;

a resistor connected for negative feedback between said output terminal and said input terminal;

a conductive shield interposed between said resistor and said integrated amplifier circuit means, said conductive shield being electrically coupled to said reference potential;

a first insulating means for electrically insulating said resistor from said conductive shield;

a second insulating means for insulating said conductive shield from said integrated circuit amplifier means;

wherein said conductive shield is disposed to reduce stray parasitic capacitance thereby increasing said shielded amplifier uniform gain over a predetermined bandwidth.

2. The shielded amplifier of claim 1, wherein said conductive shield has a top and bottom surface, said first insulating means being formed as a thin layer of first insulator material on said top surface;

whereby said thin layer of first insulator material acts to insulate said resistor from said conductive shield.

3. The shielded amplifier of claim 1, wherein said second insulating means is formed of as a thin layer of second insulator material on said base substrate first surface, said thin layer covering said integrated amplifier circuit means;

whereby said integrated amplifier circuit is insulated by said thin layer of second insulator material from said conductive shield.

4. The shielded amplifier of claim 2, wherein said resistor is a film resistor, formed on said thin layer of first insulator material on said conductive shield top surface at a predetermined location, said location being adapted to minimize electrical path lengths to said resistor as said resistor is connected for negative feedback between said output terminal and said input terminal;

whereby stray parasitic capacitance is reduced.

5. The shielded amplifier of claim 1, wherein said base substrate further comprises,

a plurality of vertically diffused, degeneratively doped, shield regions, said shield regions being electrically coupled to said reference potential and which are adapted to form a discontinuous perimeter enclosing a region of near intrinsic semiconductor material said integrated amplifier circuit means being formed within said region of near intrinsic semiconductor material, whereby said shield regions reduce said stray parasitic capacitance;

thereby increasing said shielded amplifier uniform gain over a predetermined bandwidth.

6. The shielded amplifier of claim 4, wherein said second insulating means is formed of as a thin layer of second insulator material on said base substrate first surface, said thin layer covering said integrated amplifier circuit means;

whereby said integrated amplifier circuit is insulated by said thin layer of second insulator material from said conductive shield.

7. The shielded amplifier of claim 6, further comprising means for attaching said conductive shield bottom surface to the surface of said substrate thin layer of second insulating material, said conductor shield being positioned on said second insulating material surface to minimize electrical path lengths from said output terminal to said resistor and from said resistor to said input terminal whereby parasitic capacitance is minimized.

8. The shielded amplifier of claim 7, wherein said base substrate further comprises,

a plurality of vertically diffused, degeneratively doped, shield regions, said shield regions being electrically coupled to said reference potential and which are adapted to form a discontinuous perimeter enclosing a region of near intrinsic semiconductor material said integrated amplifier circuit means being formed within said region of near intrinsic semiconductor material, whereby said shield regions reduce said stray parasitic capacitance;

thereby increasing said shielded amplifier uniform gain over a predetermined bandwidth.

9. The shielded amplifier of claim 8, further comprising, a first and second lead, and wherein said resistor further comprises,

a first terminal and,

a second terminal, and

wherein said resistor first terminal is positioned in close relation with said input terminal, said resistor first terminal being connected to said input terminal by said first lead and said resistor second terminal is positioned in close relation with said output terminal, said resistor second terminal being connected with said amplifier output terminal by said second lead, whereby said leads are short and minimize parasitic capacitance.

10. The shielded amplifier of claim 9, wherein the integrated amplifier circuit means is adapted to operate with a high impedance signal source having a source impedance in excess of 10⁺¹⁰ ohms and said resistor has a source impedance in excess of 10⁺⁹ ohms.

11. The shielded amplifier of claim 9, wherein said first insulating means is a layer of SiO₂ having a predetermined thickness and being formed on said conductive shield whereby said SiO₂ acts to insulate said resistor from said conductive shield.

12. The shielded amplifier of claim 9, wherein said second insulating means is formed as a thin layer of silox on said base substrate first surface, said thin layer covering said integrated circuit amplifier means, said second insulating means being masked to expose said input and output terminals.

13. The shielded amplifier of claim 12, wherein said first insulating means is a layer of SiO₂ having a predetermined thickness and being formed on said conductive shield whereby said SiO₂ acts to insulate said resistor from said conductive shield.

14. The shielded amplifier of claim 13, wherein said high impedance signal source has a source impedance in excess of 10⁺¹¹ ohms and said resistor has a source impedance in excess of 10⁺⁹ ohms.