Double sample active pixel sensor with double sampling temperature sensor
View Patent ↗A system which operates to determine temperature of an image sensor using the same signal chain that is used to detect the image sensor actual outputs. A correlated double sampling circuit is used to obtain the image outputs. That's same correlated double sampling circuit is used to receive two different inputs from the temperature circuit, and to subtract one from the other. The temperature output can be perceived, for example, once each frame.
1. A temperature sensing circuit for an image processing device, comprising:
a bandgap circuit for producing a pair of output signals, one of the pair of output signals being related to a temperature of at least one component in the bandgap circuit, said bandgap circuit requiring a transient start-up current;
a start-up current producing circuit, producing the transient start-up current and sensing operation of said bandgap circuit and reducing said transient start-up current relative to a duration of said sensed operation of said bandgap circuit; and
a double sampling circuit for receiving the output signals and for receiving pairs of pixel signals from a coupled image array, said double sampling circuit configured to obtain a temperature difference between the output signals.
2. A temperature sensing circuit as in claim 1 , wherein said start-up circuit includes a current mirror which conducts current once the bandgap circuit operation has started, to reduce a value of said start current.
3. The temperature sensing circuit as in claim 1 , wherein the double sampling circuit comprises:
a sample and hold circuit for receiving the output signals and pairs of pixel signals; and
a difference circuit coupled to the sample and hold circuit for outputting the temperature difference.
4. The temperature sensing circuit as in claim 1 , wherein one of the pair of output signals is a temperature and voltage stabilized output reference signal.
5. The temperature sensing circuit as in claim 4 , wherein the output signal related to a temperature of at least one component varies in relation to the reference signal.
6. The temperature sensing circuit as in claim 1 , wherein each pair of pixel signals includes a signal from a pixel prior to light integration and a signal from said pixel after light integration.
7. The temperature sensing circuit as in claim 1 , wherein said transient start-up current is reduced to zero after the bandgap circuit begins operation.
8. The temperature sensing circuit as in claim 1 , further comprising a level shifting circuit for lowering an output impedance of said bandgap circuit.