Internal bias measure with onboard ADC for electronic devices
View Patent ↗An apparatus and method for on-chip bias measurement of an analog signals on an integrated circuit with a switchable analog-to-digital converter capable of performing testing and other types of processing. Analog signal test locations are selected for testing by a test input selector which is in turn controlled by a controller on an integrated circuit, such as an imager chip. Test locations are connected to one or more analog-to-digital converters through the test input selector. The analog-to-digital converter(s) output a test measurement digital output to either test equipment or an on-chip calibration circuit. Test equipment or on-chip calibration circuits adjusts imager component bias or other operating parameters used in chip or device operation based on output from the analog-to-digital converter(s).
1. A method of testing an imager comprising a pixel array and an analog-to-digital converter, the method comprising:
transmitting a control signal from a test station to the imager;
decoupling the analog-to-digital converter from the pixel array;
selectively coupling a first of at least two analog reference signal lines to the analog-to-digital converter responsive to the control signal;
transmitting a digital value derived from the coupled analog reference signal line to the test station;
comparing the digital value to a target value corresponding to the coupled analog reference signal line;
selectively coupling a second of the at least two analog reference signal lines to the analog-to-digital converter and repeating the transmitting and comparing steps; and
programming the imager with a trim setting selected based on a result of the comparisons.
2. The method of testing an imager of claim 1 , further comprising:
selecting a different trim setting and repeating the comparison step if the digital value does not substantially match the target value.
3. The method of testing an imager of claim 2 , further comprising:
selecting an available trim setting yielding a digital value closest to the target value if a different trim setting is not available.
4. The method of testing an imager of claim 1 , further comprising:
repeating the comparing step for a plurality of trim settings; and
selecting the trim setting yielding the digital value that is a best match to the target value.
5. The method of testing an imager of claim 1 , further comprising:
repeating the transmitting the digital value and comparing steps for at least a second analog reference signal line.
6. A method of testing an imager comprising a pixel array, the method comprising:
isolating an analog-to-digital converter from column readout circuitry;
sequentially coupling at least two test nodes to the analog-to-digital converter;
comparing a digital value from the analog-to-digital converter corresponding to each test node to a respective reference value; and
programming the imager with at least one setting selected based on a result of the comparisons,
wherein each of the at least two test nodes is associated with a different analog reference signal.
7. The method of testing an imager of claim 6 , wherein the isolating step comprises opening a switch coupled between the pixel array and the analog-to-digital converter.
8. The method of testing an imager of claim 6 , further comprising:
repeating the coupling and comparing steps after programming the imager.
9. The method of testing an imager of claim 8 , further comprising:
adjusting the at least one programmed setting based on a result of the repeated comparing step.
10. The method of testing an imager of claim 6 , wherein at least one of the plurality of test nodes corresponds to a pixel of the pixel array.
11. The method of claim 6 , wherein the sequential coupling comprises coupling a first test node, performing the comparing step, decoupling the first test node, coupling a second test node, and repeating the comparing step.
12. A method of testing an imager comprising a pixel array coupled to an input of an analog-to-digital converter, the method comprising:
decoupling the pixel array and the analog-to-digital converter;
coupling a first of at least two analog reference signal lines to the input of the analog-to-digital converter;
generating by the analog-to-digital converter a digital value derived from the coupled first analog reference signal line;
comparing the digital value to a predetermined target value associated with the coupled first analog reference signal line;
decoupling the first analog reference signal line from the analog-to-digital converter
coupling a second of the at least two analog reference signal lines to the input of the analog-to-digital converter;
repeating the generating and comparing steps for the second analog reference signal line; and
adjusting a trim setting of the imager based on a result of the comparisons.
13. The method of claim 12 , further comprising repeating the coupling, generating and comparing steps after adjusting the trim setting.
14. A method of testing an imager comprising a pixel array and an analog-to-digital converter, the method comprising:
opening a switch coupled between the pixel array and the analog-to-digital converter to decouple the pixel array from the analog-to-digital converter;
sequentially applying first and second analog reference signals to the analog-to-digital converter by sequentially coupling at least two analog reference signal lines to the analog-to-digital converter;
converting the analog reference signals to respective digital values;
comparing the digital values to respective predetermined target values corresponding to the analog reference signals; and
programming the imager based on a result of the comparison.
15. The method of claim 14 , wherein the opening and applying steps are responsive to commands received by the imager from an external test station coupled to the imager via a communications channel.
16. The method of claim 14 , further comprising repeating the converting and comparing steps after the programming step if the digital value does not match the target value.