Differential current mode output circuit for electro-optical sensor arrays

• US 6,344,651 B1
• Filed: 10/27/1999
• Issued: 02/05/2002
• Est. Priority Date: 04/20/1999
• Status: Expired due to Term

• Current Assignee: Raytheon Company (Rtx Corporation), FLIR Systems, Inc. (Teledyne Technologies Incorporated)
• Original Assignee: Raytheon Company (Rtx Corporation), Indigo Systems Corporation (Telecom Eireann)
• Inventors: Woolaway, James T., Black, Stephen H., Parrish, William J.
• Primary Examiner(s): Hannaher, Constantine
• Application Number:
  US09/427,645
• Time in Patent Office: 832 Days
• Field of Search: 330/252, 330/253, 330/257, 330/277, 330/288, 330/308, 327/52, 327/53, 327/56, 327/77, 327/89, 327/563, 250/332, 250/338.4, 250/370.08
• US Class Current: 250/370.08
• CPC Class Codes: G01J 5/24 Use of specially adapted circuits, e.g. bridge circuits
• CPC Class Codes: H03F 2203/45652 the LC comprising one or more further dif amp stages, either identical to the dif amp or not, in cascade
• CPC Class Codes: H03F 2203/45658 the LC comprising two diodes of current mirrors
• CPC Class Codes: H03F 2203/45682 the LC comprising one or more op-amps
• CPC Class Codes: H03F 3/082 with FET's H03F3/085 takes precedence
• CPC Class Codes: H03F 3/45197 Pl types H03F3/45224, H03F3/45251 take precedence
• CPC Class Codes: H03F 3/68 Combinations of amplifiers, e.g. multi-channel amplifiers for stereophonics power amplifiers using a combination of several semiconductor amplifiers H03F3/211; combinations of amplifiers using coupling networks with distributed constants H03F3/602
• CPC Class Codes: H04N 5/33 Transforming infrared radiation cameras or camera modules for generating image signals from infrared radiation H04N23/20; circuitry of SSIS for transforming infrared radiation into image signals H04N25/20

Abstract

A differential current mode amplifier circuit (5,5′) includes a first circuit leg having a first current source providing a current I1 coupled in series with a first transistor (m1) at a first circuit node (n1). The first transistor has a control terminal for coupling to an input signal potential (Vs). Vs is obtained from a unit cell of a radiation detector array, and is indicative of a magnitude of an integrated, photon-induced charge. The first circuit leg outputs a first output current (Is). A second circuit leg includes a second current source providing a current I2 coupled in series with a second transistor (m2) at a second circuit node (n2). The second transistor has a control terminal for coupling to an input reference potential (Vr). The second circuit leg outputs a second output current (Ir). A resistance (Rs) is coupled between the first circuit leg and the second circuit leg at the first circuit node and the second node. The current flow through Rs is proportional to a difference between Vs and Vr, and is thus indicative of a magnitude of Vs.

Claims

1. A differential current mode amplifier circuit, comprising:

a first circuit leg comprising a first current source providing a current I1 coupled in series with a first transistor at a first circuit node, said first transistor having a control terminal for coupling to an input signal potential (Vs), said first circuit leg outputting a first output current;

a second circuit leg comprising a second current source providing a current I2 coupled in series with a second transistor at a second circuit node, said second transistor having a control terminal for coupling to an input reference potential (Vr), said second circuit leg outputting a second output current; and

a resistance (Rs) coupled between said first circuit leg and said second circuit leg at said first circuit node and said second node.

2. A differential current mode amplifier circuit as in claim 1, wherein the current flow through Rs is proportional to a difference between Vs and Vr.

3. A differential current mode amplifier circuit as in claim 1, wherein the current flow through Rs (I(Rs)) is described by:

4. A differential current mode amplifier circuit as in claim 3, wherein Is is input to a first transimpedance amplifier, wherein Ir is input to a second transimpedance amplifier, and wherein a voltage output of said first transimpedance amplifier and a voltage output of said second transimpedance amplifier are input to a differential analog to digital converter which outputs a digital indication of the magnitude of Vs.

5. A differential current mode amplifier circuit as in claim 1, wherein said first and second current sources are each a constant current source comprised of a transistor having a control terminal coupled to an output of a current mirror.

6. A differential current mode amplifier circuit, comprising:

a first circuit leg comprising a first current source providing a current I1 coupled in series with a first MOSFET at a first circuit node, said first MOSFET having a gate terminal for coupling to an input signal potential (Vs) derived from an output of an electromagnetic radiation sensor, said first circuit leg being coupled to a first mirrored circuit leg for outputting a first output current A*Is, where A is a multiplication factor and Is is the current flow though said first MOSFET;

a second circuit leg comprising a second current source providing a current I2 coupled in series with a second MOSFET at a second circuit node, said second MOSFET having a gate terminal for coupling to an input reference potential (Vr), said second circuit leg being coupled to a second mirrored circuit leg for outputting a second output current A*Ir, where Ir is the current flow though said second MOSFET; and

a resistance (Rs) coupled between said first circuit leg and said second circuit leg at said first circuit node and said second node such that the current flow through Rs (I(Rs)) is proportional to a difference between Vs and Vr and is described by;

7. A differential current mode amplifier circuit as in claim 6, wherein A*Is is input to a first transimpedance amplifier, wherein A*Ir is input to a second transimpedance amplifier, and wherein a voltage output of said first transimpedance amplifier and a voltage output of said second transimpedance amplifier are input to a differential analog to digital converter which outputs a digital indication of the magnitude of Vs.

8. A differential current mode amplifier circuit as in claim 6, wherein said first and second current sources are each a constant current source comprised of a MOSFET having a gate terminal coupled to an output of a current mirror.

9. A differential current mode amplifier circuit as in claim 6, wherein said first circuit leg and said second circuit leg are each comprised of a current mirror for generating A*Is and A*Ir from Is and Ir, respectively.

10. A differential current mode amplifier circuit as in claim 6, wherein said electromagnetic radiation sensor is part of a two dimensional array having N rows and M columns of electromagnetic radiation sensors disposed on a first substrate, wherein there is one of said differential current mode amplifier circuits disposed on a second substrate, and wherein Vs is derived sequentially from individual ones of said N rows being multiplexed into one of said M columns, and individual ones of said M columns being multiplexed into said gate of said first MOSFET through an output bus.

11. A differential current mode amplifier circuit as in claim 6, wherein said electromagnetic radiation sensor is part of a two dimensional array having N rows and M columns of electromagnetic radiation sensors disposed on a first substrate, wherein there are M ones of said differential current mode amplifier circuits disposed on a second substrate, and wherein Vs is derived sequentially from individual ones of said N rows being multiplexed into one of said M columns, and individual ones of said M columns being multiplexed to an output bus via said gate of said first MOSFET of an associated individual one of said M differential current mode amplifier circuits.

12. A differential current mode amplifier circuit as in claim 11, wherein said output bus is comprised of a first signal line that is coupled in common to a first output of each of said M differential current mode amplifier circuits for outputting A*Is, and wherein said output bus is further comprised of a second signal line that is coupled in common to a second output of each of said M differential current mode amplifier circuits for outputting A*Ir.

13. A differential current mode amplifier circuit as in claim 11, wherein said columns are multiplexed by sequentially activating control signals that are coupled to said first and second current sources of individual ones of said M differential current mode amplifier circuits for turning said first and second current sources on and off, and wherein said control signals are activated so as to overlap such that said first and second current sources of one of said differential current mode amplifier circuits are turned on before said first and second current sources of another one of said differential current mode amplifier circuits are turned off.

14. An IR-FPA, comprising:

an array of IR responsive photodetectors; and

a readout integrated circuit (ROIC) coupled to said array, said ROIC comprising at least one differential current mode amplifier output circuit having a first input for inputting a first potential Vs representing, at a particular time, a signal output from one of said IR responsive photodetectors and a second input for inputting a second potential Vr representing a reference potential, said at least one differential current mode amplifier output circuit outputting first and second currents, wherein a difference between said first and second currents is indicative of a difference between Vs and Vr.

15. A method of operating an electro-optical sensor array, comprising steps of:

converting incident photons to charge and integrating the charge in unit cells of the sensor array;

sequentially sampling the integrated charge from the unit cells and converting the sampled charge to a signal potential Vs; and

applying Vs and a reference potential Vr to a differential current mode amplifier output circuit and outputting first and second currents, wherein a difference between the first and second currents is indicative of a difference between Vs and Vr.

16. A radiation sensor unit, comprising:

an electro-optical sensor array for converting incident photons to charge and for integrating the charge in unit cells of the sensor array;

a multi-channel readout circuit for sequentially sampling the integrated charge from the unit cells and comprising, in each channel, an amplifier circuit for converting the sampled charge to a signal potential Vs; and

a channel multiplexer for sequentially applying Vs from a plurality of channels to an input of a differential current mode amplifier output circuit, said differential current mode amplifier output circuit being responsive to Vs and to a reference potential Vr for outputting first and second currents, wherein a difference between said first and second currents is indicative of a difference between Vs and Vr.

17. A radiation sensor unit as in claim 16, wherein said amplifier circuit is comprised of a charge transimpedance amplifier (CTIA).

18. A radiation sensor unit as in claim 16, wherein said amplifier circuit is comprised of an auto-zero charge transimpedance amplifier (CTIA).

19. A radiation sensor unit, comprising:

an electro-optical sensor array for converting incident electromagnetic radiation to charge and for integrating the charge in unit cells of the sensor array;

a multi-channel readout circuit for sequentially sampling the integrated charge from the unit cells and comprising, in each channel, an amplifier circuit for converting the sampled charge to a signal potential Vs; and

each channel further comprises a differential current mode amplifier output circuit, said differential current mode amplifier output circuit being responsive to Vs output from the associated amplifier circuit and to a reference potential Vr for outputting first and second currents, wherein a difference between said first and second currents is indicative of a difference between Vs and Vr.

20. A radiation sensor unit as in claim 19, wherein said amplifier circuit is comprised of a charge transimpedance amplifier (CTIA).