Low cost and high performance bolometer circuitry and methods

Patent metadata

Field	Value
Publication number	US-10197448-B2
Application number	US-201715484989-A
Country	US
Kind code	B2
Filing date	Apr 11, 2017
Priority date	Oct 16, 2014
Publication date	Feb 5, 2019
Grant date	Feb 5, 2019

Abstract

A bolometer circuit may include an active bolometer configured to receive external infrared (IR) radiation and a resistive load, which are configured to be connected in series in a bolometer conduction path from a supply voltage node to a common voltage node. A node in the bolometer conduction path between the resistive load and the active bolometer is coupled to a first input of an op-amp. A variable voltage source is coupled to a second input of the op-amp to provide a reference voltage level. The op-amp maintains the reference voltage level at the first input to generate a current flow in response to a resistance change of the active bolometer due to the external IR radiation. The amplifier circuit may be configured as a feedback amplifier or an integrating amplifier. The bolometer circuit may be configured to enable a low-power mode of operation.

First claim

What is claimed is:

1. A bolometer circuit, comprising:
a substrate;
an active bolometer configured to receive external infrared (IR) radiation and substantially thermally isolated from the substrate;
a first resistive load, wherein the active bolometer and the first resistive load are configured to be connected in series in a bolometer conduction path from a supply voltage node to a common voltage node;
an amplifier circuit comprising an operational amplifier (op-amp) having a first input coupled to a node in the bolometer conduction path between the first resistive load and the active bolometer; and
a variable voltage source coupled to a second input of the op-amp, wherein the variable voltage source is configured to provide a reference voltage level, wherein the variable voltage source comprises a reference conduction path comprising a blind bolometer and a second resistive load configured to be connected in series from the supply voltage node to the common voltage node, wherein the blind bolometer is shielded from the external IR radiation, thermally isolated from the substrate, and configured to track self-heating of the active bolometer,
wherein the amplifier circuit is configured to generate a current flow to the amplifier circuit in response to a resistance change of the active bolometer due to the external IR radiation by maintaining the reference voltage level at the first input of the op-amp, and
wherein the amplifier circuit is further configured to convert the current flow into an output voltage at an output of the op-amp that is indicative of an intensity of the external IR radiation received at the active bolometer.

2. The bolometer circuit of claim 1 , wherein:
the first resistive load comprises a thermally shorted bolometer that is thermally shorted to the substrate to operate as a temperature-compensated load for the bolometer conduction path;
a resistance of the first resistive load is similar to a resistance of the active bolometer;
the amplifier circuit is configured to adjust a voltage offset at the first input of the op-amp, the second input of the op-amp, or both in response to offset adjustment bits, so as to adjust a bias across the active bolometer;
the bolometer circuit is configured to operate in a normal mode or in a low-power mode based on selective opening or closing of a plurality of switches associated with the bolometer conduction path and the amplifier circuit;
in the normal mode, the output of the op-amp provides the output voltage indicative of the intensity of the external IR radiation received at the active bolometer; and
in the low-power mode, the output of the op-amp is driven to a predetermined voltage level and the op-amp, the bolometer conduction path, or both are disconnected from power.

3. The bolometer circuit of claim 1 , further comprising a low-pass filter (LPF) coupled to the output of the op-amp to filter the output voltage to reduce high-frequency noise, wherein:
the amplifier circuit comprises a resistive gain coupling the output of the op-amp to the first input of the op-amp to configure the amplifier circuit as a feedback amplifier;
the resistive gain comprises a thermally shorted bolometer that is thermally shorted to the substrate to operate as a temperature-compensated gain for the amplifier circuit;
the amplifier circuit is configured to maintain, in response to the reference voltage level, a bias voltage across the active bolometer and a load bias voltage across the first resistive load via the first input of the op-amp coupled to the node in the bolometer conduction path;
the current flow to the amplifier circuit is generated in response to a difference between a current generated by the load bias voltage being applied to the first resistive load and a current generated by the bias voltage being applied to the active bolometer that exhibits the resistance change due to the external IR radiation; and
the amplifier circuit is configured to generate the output voltage in response to the current flow flowing through the resistive gain.

4. The bolometer circuit of claim 1 , wherein:
the second resistive load has a similar resistance as the first resistive load; and
the reference voltage level provided by the variable voltage source is provided from a node in the reference conduction path between the blind bolometer and the second resistive load, such that the current flow to the amplifier circuit is adjusted to compensate for the self-heating of the active bolometer.

5. The bolometer circuit of claim 1 , further comprising:
a plurality of the active bolometers arranged in a focal plane array (FPA) having columns and rows;
a plurality of column circuits each associated with a column of the FPA and comprising a respective resistive load and a respective amplifier circuit; and
a plurality of row-select switches associated with the respective active bolometers and configured to selectively connect the respective active bolometers to the corresponding resistive loads of the column circuits to generate output voltages for the active bolometers in a row-by-row fashion according to timing and control signals.

6. The bolometer circuit of claim 1 , wherein:
the first resistive load comprises a thermally shorted bolometer and a transistor connected in series to operate as a current source that generates a load current to the active bolometer;
the thermally shorted bolometer is thermally shorted to the substrate to operate as a temperature-compensated load for the bolometer conduction path;
a resistance of the thermally shorted bolometer is larger than a resistance of the active bolometer; and
the supply voltage node is configured to provide a supply voltage level that is higher than a nominal voltage level applicable to generate the load current in a nominal case of the thermally shorted bolometer having a resistance similar to the resistance of the active bolometer.

7. The bolometer circuit of claim 6 , wherein:
the transistor comprises a metal oxide semiconductor field effect transistor (MOSFET);
the variable voltage source is a first variable voltage source; and
the bolometer circuit further comprises a second variable voltage source configured to provide a variable voltage level to the gate of the MOSFET, the MOSFET being configured to adjust the load current in response to the variable voltage level.

8. The bolometer circuit of claim 7 , wherein:
the first resistive load comprises a first thermally shorted bolometer and a first MOSFET;
the second resistive load comprises a second thermally shorted bolometer and a second MOSFET connected in series to operate as a current source;
the reference voltage level provided by the first variable voltage source is provided from a node in the reference conduction path between the blind bolometer and the second resistive load, such that the current flow to the amplifier circuit is adjusted to compensate for the self-heating of the active bolometer; and
the variable voltage level from the second variable voltage source is provided to the gates of the first and the second MOSFETs to adjust currents generated by the first and the second resistive loads.

9. The bolometer circuit of claim 6 , wherein:
the amplifier circuit further comprises:
a capacitor coupling the output of the op-amp to the first input of the op-amp to configure the amplifier circuit as an integrating amplifier;
a buffer connected to the node in the bolometer conduction path; and
a resistor connected to the first input of the op-amp, the buffer and the resistor being connected in series to couple the node in the bolometer conduction path to the first input of the op-amp;

the amplifier circuit is configured to maintain the reference

Assignees

• Flir Systems

Inventors

• Simolon Brian B
• Aziz Naseem Y
• Nussmeier Mark T
• Cannata Robert F

Classifications

• G01J2005/0077

  Imaging · CPC title

• G01J5/24 Primary

  Use of specially adapted circuits, e.g. bridge circuits · CPC title

• G01J1/44

  Electric circuits {(for command of an exposure part G03B7/02)} · CPC title

• G01J2005/202

  Arrays · CPC title