Quiescent signal compensated photodetector system for large dynamic range and high linearity

• US 5,057,682 A
• Filed: 11/05/1990
• Issued: 10/15/1991
• Est. Priority Date: 12/26/1989
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Brown, Dale M., Michon, Gerald J.
• Primary Examiner(s): Nelms, David C.
• Application Number:
  US07/607,222
• Time in Patent Office: 344 Days
• Field of Search: 250/214 A, 250/214 C, 250/214 R, 250/208.2, 307/311
• US Class Current: 250/214.00C
• CPC Class Codes: A61B 6/032 Transmission computed tomography [CT]
• CPC Class Codes: H03F 3/082 with FET's H03F3/085 takes precedence
• CPC Class Codes: H04N 25/63 applied to dark current
• CPC Class Codes: H04N 25/701 Line sensors
• CPC Class Codes: H04N 25/78 Readout circuits for addressed sensors, e.g. output amplifiers or A/D converters
• CPC Class Codes: H04N 3/1512 for MOS image-sensors, e.g. MOS-CCD H04N3/1581 takes precedence
• CPC Class Codes: H04N 3/1568 for disturbance correction or prevention within the image-sensor, e.g. biasing, blooming, smearing correction circuits H04N25/62
• CPC Class Codes: H05G 1/26 Measuring, controlling or protecting measuring X-ray radiation G01T

Abstract

The linearity and dynamic range of a photodetector system is enhanced by providing real time cancellation of condition-dependent quiescent output signals from the photosensitive devices by provision of a condition-dependent output signal monitoring device which drives the input section of a current mirror having output sections connected to the active photosensitive devices to zero out the condition-dependent quiescent output signals of those photosensitive devices during system operation. Multiple output sections may be run from a single input section of the current mirror.

Claims

1. A photodetector system comprising:

a plurality of photosensitive devices which exhibit a condition-dependent quiescent output signal;

a plurality of output circuits each connected to receive the output signal from a different one of said photosensitive devices;

a quiescent signal monitor device having a condition-dependent quiescent output signal which is proportional to that of said photosensitive devices;

means for shielding said monitor device from the light to be sensed by said photosensitive devices, whereby the output signal from said monitor device is proportional to the condition-dependent-quiescent-output-signal contributions to the output signals of said photosensitive devices;

current mirror means responsive to the output signal from said monitor device for applying quiescent output signal compensating signals to a plurality of said output circuits to compensate for the condition-dependent-quiescent-output-signal contribution to the output signal of each of said photosensitive devices, whereby the output from each of said output circuits is substantially independent of the condition-dependent quiescent output signal of the one of said photosensitive devices to which it is coupled.

2. The photodetector system recited in claim 1 said photosensitive devices are continuous output

said photosensitive devices are continuous output devices.

3. The photodetector system recited in claim 2 wherein:

said quiescent signal is a current.

4. The photodetector system recited in claim 1 wherein:

said monitor device is a different size than at least some of said photosensitive devices; and

said current mirror means scales the signal applied to said output circuits in accordance with the relative sizes of said monitor device and said photosensitive devices.

5. The photodetector system recited in claim 4 wherein:

said quiescent signal is a current.

6. The photodetector system recited in claim 1 wherein:

said monitor device is a different size than at least some of said photosensitive devices;

not all of said photosensitive devices are the same size; and

said current mirror means scales the signal applied to said output circuits in accordance with the relative sizes of said monitor device and said photosensitive devices.

7. The photodetector system recited in claim 6 wherein:

said quiescent signal is a current.

8. The photodetector system recited in claim 1 further comprising:

a second monitor device coupled to said current mirror means in a manner to combine the condition-dependent quiescent output signals derived from the first recited and said second monitor devices to more accurately compensate said photosensitive devices of said photodetector system.

9. The photodetector system recited in claim 8 wherein:

said photosensitive devices are arranged in a linear array extending in a first direction and said monitor devices are disposed on opposite sides of said linear array in a second direction disposed at an angle to said first direction.

10. The photodetector system recited in claim 8 wherein:

said photosensitive devices are arranged in a linear array extending in a first direction and said monitor devices are spaced apart and disposed in the vicinity of opposite ends of said linear array.

11. The photodetector system recited in claim 10

said monitor devices are disposed on opposite sides of said linear array in a second direction disposed at an angle to said first direction.

12. A photodetector system comprising:

a photosensitive device which exhibits a condition-dependent quiescent output signal;

an output circuit connected to receive the output signal from said photosensitive device;

a quiescent output signal monitor device having a condition-dependent-quiescent-output-signal response which is proportional to that of said photosensitive device;

means for shielding said monitor device from the light to be sensed by said photosensitive device, whereby the output signal from said monitor device is proportional to the condition-dependent-quiescent-output-signal contribution to the output signal from said photosensitive device;

current mirror means responsive to said monitor device for applying a condition-dependent-quiescent-output-signal-compensating signal to said output circuit to compensate for the condition-dependent quiescent output signal from said photosensitive device whereby the output from said output circuit is substantially independent of the condition-dependent quiescent output signal of said photosensitive device.

13. A photodetector system comprising:

a continuous output photosensitive device which exhibits a condition-dependent quiescent current;

an output circuit connected to receive the output current from said photosensitive device;

a quiescent current monitor device having a condition-dependent quiescent current response which is proportional to that of said photosensitive device;

means for shielding said monitor device from the light to be sensed by said photosensitive device, whereby the output of said monitor device is proportional to the condition-dependent quiescent current contribution to the output signal from said photosensitive device;

current mirror means responsive to said monitor device for applying a condition-dependent-quiescent-current-compensating signal to said output circuit to compensate for the condition-dependent quiescent current from said photosensitive device whereby the output from said output circuit is substantially independent of the condition-dependent quiescent current of said photosensitive device.

14. A photodetector system comprising:

a plurality of continuous output photosensitive devices which exhibit condition-dependent quiescent output signals;

a plurality of output circuits each connected to receive the output signal from a different one of said photosensitive devices;

a quiescent output signal monitor device having a condition-dependent quiescent output which is proportional to that of said photosensitive devices;

means for shielding said monitor device from the light to be sensed by said photosensitive devices, whereby the output signal from said monitor device is proportional to the condition-dependent-quiescent-output-signal contributions to the output signals from said photosensitive devices; and

current mirror means responsive to the output signal from said monitor device for applying condition-dependent-quiescent-output-signal-compensating signals to a plurality of said output circuits to compensate for the condition-dependent quiescent output from each of said photosensitive devices, whereby the output from each of said output circuits is substantially independent of the condition-dependent quiescent output of the one of said photosensitive devices to which it is coupled.

15. The photodetector system recited in claim 14 wherein:

said quiescent output signal is a current.

16. The photodetector system recited in claim 15 wherein:

said monitor device is a different size than at least some of said photosensitive devices; and

said current mirror means scales the signal applied to said output circuits in accordance with the relative sizes of said monitor device and said photosensitive devices.

17. The photodetector system recited in claim 15 further comprising:

a second monitor device coupled to said current mirror means in a manner to combine the condition-dependent quiescent currents derived from the first recited and said second monitor devices to more accurately compensate said photosensitive devices of said photodetector system.

18. The photodetector system recited in claim 17 wherein:

said photosensitive devices are arranged in a linear array extending in a first direction and said monitor devices are disposed on opposite sides of said linear array in a second direction disposed at an angle to said first direction.

19. The photodetector system recited in claim 17 wherein:

said photosensitive devices are arranged in a linear array extending in a first direction and said monitor devices are spaced apart and disposed in the vicinity of opposite ends of said linear array.

20. The photodetector system recited in claim 19 wherein:

said monitor devices are disposed on opposite sides of said linear array in a second direction disposed at an angle to said first direction.

21. A photodetector system comprising:

a continuous output photosensitive device which exhibits a condition-dependent quiescent current;

an output circuit connected to receive the output current from said photosensitive device;

a condition-dependent quiescent current monitor device having a condition-dependent-quiescent-current response which is proportional to that of said photosensitive device;

means for shielding said monitor device from the light to be sensed by said photosensitive device, whereby the output of said monitor device is proportional to the condition-dependent-quiescent-current contribution to the output signal from said photosensitive device;

current mirror means responsive to said monitor device for applying a condition-dependent-quiescent-current-signal compensating signal to said output circuit to compensate for the condition-dependent quiescent current from said photosensitive device whereby the output from said output circuit is substantially independent of the condition-dependent quiescent current of said photosensitive device.

22. A current mirror comprising:

an input section including a monitor device and an input control device connected to in a manner in which a reference output signal from said monitor device biases said input control device to provide said output signal;

a plurality of output sections each including;

an output control device, and

a compensated device connected to said output control device in a manner corresponding to the connection of said monitor device to said input control device;

said monitor and compensated devices having corresponding characteristics whereby, said current mirror conducts the reference portions of the output signals of said compensated devices.

23. The current mirror recited in claim 22 wherein:

said monitor device reference output signal is a condition-dependent quiescent output signal whereby said current mirror compensates the output circuits of said compensated devices for the condition-dependent-quiescent-output-signal portions of the output signals of said compensated devices.

24. The current mirror recited in claim 23 wherein:

said compensated devices are continuous output devices.

25. The current mirror recited in claim 24 wherein:

said quiescent signal is a current.

26. The current mirror recited in claim 22 wherein:

said monitor device is a different size than at least some of said compensated devices; and

said current mirror means scales the signal applied to said output circuits in accordance with the relative sizes of said monitor device and said compensated devices.

27. The current mirror recited in claim 26 wherein:

said quiescent signal is a current.

28. The current mirror recited in claim 22 wherein:

said monitor device is a different size than at least some of said compensated devices;

not all of said compensated devices are the same size; and

said current mirror means scales the signal applied to said output circuits in accordance with the relative sizes of said monitor device and said compensated devices.

29. The current mirror recited in claim 28 wherein:

said quiescent signal is a current.

30. The current mirror recited in claim 22 further comprising:

a second monitor device coupled to said current mirror means in a manner to combine the condition-dependent quiescent output signals derived from the first recited and said second monitor devices to more accurately compensate said compensated devices.