Patent Application
20190068927
This disclosure relates generally to ultra-small image sensors. In particular, the clock and/or data/control signal transmission lines of an ultra-small image sensor utilize optical fibers to transmit signals digitally. An ultra-small image sensor is a class of image sensors with a product package size of about 1 mm×1 mm, or less. Conventionally, image sensors use conductor-based electrical transmission lines to transmit electrical signals. In the current disclosure, optical fibers are used to replace conventional transmission lines for the clock and/or the data/control signal transmission.
An image sensor uses opto-electronic components, such as photodiodes, to detect incoming light and produce electronic signals in response. A primary component of the image sensor is its sensor pixel array, wherein each pixel includes a photodiode to convert photons to charge carriers, a floating node to temporarily store the charge carries, and a number of transistor gates (transfer gate, source follower, reset transistor, etc.) to convey the charge carriers out of the pixel to be further processed by a peripheral supporting circuitry. An image sensor is often packaged with its supporting module into an image sensor system package, which is then incorporated into a final imaging product such as a mobile phone camera, a consumer electronic camera, a surveillance video camera, an automotive driver assistance system, an industrial imaging borescope, a medical imaging endoscope, etc. The supporting module may provide power and ground connections to the image sensor. Additionally, the supporting module may send control signals, including clock signals, to the image sensor. In return, the image sensor may send image data signals, such as video signals to the supporting module to be further processed into output images. Transmission lines are conventionally used to couple the image sensor with its supporting module.
Non-limiting and non-exhaustive examples of the invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.
In the following description, numerous specific details are set forth to provide a thorough understanding of the examples. One skilled in the relevant art will recognize; however, that the techniques described herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring certain aspects.
Reference throughout this specification to “example” or “embodiment” means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example of the present invention. Thus, the appearances of “example” or “embodiment” in various places throughout this specification are not necessarily all referring to the same example. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more examples.
Throughout this specification, several terms of art are used. These terms are to take on their ordinary meaning in the art from which they come, unless specifically defined herein or the context of their use would clearly suggest otherwise.
First Image Sensor System Embodiment
Due to the ultra-small dimension of the image sensor 110, many of its control and data signal processing function need to be performed elsewhere outside the sensor, for example, by the supporting module 170, which may perform as a controller, a power source, and other supporting functions. More particularly, the supporting module 170 may include a bridge 180, which includes functional blocks such as analog-digital converter (ADC), decoder, image signal processor (ISP), etc. To maintain the ultra-small dimension of the image sensor 110, its internal circuitry may be minimized. For example, only circuits directly relating to image sensing are kept inside the image sensor 110. Circuits performing other functions are placed outside the image sensor 110. For example, they are placed inside the supporting module 170. In addition, the number of transmission lines that couple the image sensor 110 with the supporting module 170 is minimized to be only four lines. Specifically, there is a power line 140, a ground line 150, a data/control signal line 130, and a clock line 160. The ultra-small dimension of the image sensor 110 entails that only four transmission lines may be accommodated by it. There is no room for additional transmission lines going into the image sensor 110.
Similarly, for the power line 140 and the clock line 160, the image sensor 110 includes a sensor-side power line coupler 141 and a sensor-side clock line coupler 161, respectively; the supporting module 170 includes a module-side power line coupler 145 and a module-side clock line coupler 165, respectively. The power line 140 connects the two power line couplers 141 and 145; the clock line 160 connects the two clock line couplers 161 and 165. Both the power line 140 and the clock line 160 are shown to be co-axial cables that each includes a conductive line core 142, 164; and a line shield 143, 163. Transmission line types other than the co-axial cable may also be viable, e.g., a twisted pair line. Each shield 143, 163 is connected to the ground line 150 with one or a number of shield grounding lines 144, 164, respectively. This grounding is desirable, but it is also optional.
All the sensor-side couplers 131, 141, 151, and 161 are connected to the internal circuit that is inside the image sensor 110. All the module-side couplers 135, 145, 155, and 165 are connected to the circuit that is inside the supporting module 170.
The ground line 150 provides an electrical grounding function. The data/control signal line 130 conveys image data signal from the image sensor 110 to the supporting module 170. It may also convey sensor control signals from the supporting module 170 to the image sensor 110. The power line 140 supplies electrical power from the supporting module 170 to the image sensor 110. The clock line 160 supplies clock signal from the supporting module 170 to the image sensor 110, as a necessary part for the timing operation of the sequential logic circuits within the image sensor system 100.
Noise Caused by a Pulse-Train Clock Signal
A major problem of the ultra-small image sensor system 100 is electronic noise caused by the clock transmission line 160. Every image sensor system requires a timing operation, so a clock line is a routine component of such an image sensor system. Clock line related noise is generally not an issue for regular size image sensors, whose width is about 2 mm or more. However, in an ultra-small image sensor, the circuit components are positioned very close to each other, so some circuit components are now more susceptible to noise generated by other components. For an ultra-small image sensor that is 1.0±0.3 mm or less, the noise caused by the periodic clock signal as transmitted by the clock line 160 becomes prominent, as disclosed further below.
The data signal waveform 230 includes a data signal 235 and a series of sharp, spike-like peaks. It is appreciated that these sharp peaks are noise that are caused by the clock pulses 220. More specifically, at each rising clock edge 221, there is a corresponding positive sharp peak 231, a corresponding negative sharp peak 232, or both, that occur at the digital waveform 230. At each falling clock edge 222, there is a corresponding negative sharp peak 233, a corresponding positive sharp peak 234, or both, that occur at the digital waveform 230. These sharp peaks that correspond with the rising and falling clock edges are confirmed to be noise that are associated with the clock signal transmission line 130, because if the clock line 130 is eliminated, then these noise peaks will be significantly reduced or disappear altogether.
As long as there is a electrical clock signal that is needed for timing operations to drive the sequential digital logic that is needed for imaging and image processing, such an electrical clock signal will likely produce its periodic noise to some degree. For an ultra-small image sensor, this clock related noise is especially pronounced. This clock-related periodic noise affects the image data signal to create dark stripes in output images, and is an undesirable feature that needs to be eliminated.
Several factors exacerbate the clock-related periodic noise. First, since the dimension of the ultra-small image sensor is only about 1.0±0.3 mm, the circuit components are placed very close to each other, so the image producing components are significantly affected by the clock components. Second, the conductor core and shield of the clock line contribute to the noise. It is appreciated that medical endoscopes only have transmission lines that are generally less than two meters, but even this relatively short distance is sufficient to exacerbate the clock noise problem for the ultra-small image sensor. Shortening the length of the clock line will reduce the clock noise, but will also negatively affect the utility of the medical endoscope.
Electronic noises are conventionally removed with filters. The primary source of the aforementioned noise is the clock transmission line 160 itself (see
Second Image Sensor System Embodiment
In
Due to the ultra-small dimension of the image sensor 310, much of its control and data signal processing function needs to be performed elsewhere outside the sensor, for example, by the supporting module 370, which may perform as a controller, a power source, and other supporting function blocks. More particularly, the supporting module 370 may include a bridge 380, which includes functional blocks such as analog-digital converter (ADC), decoder, image signal processor (ISP), etc.
Similar to the first embodiment of the image sensor system 100 in
Similarly, for the power line 340, the image sensor 310 includes a sensor-side power line coupler 341; the supporting module 370 includes a module-side power line coupler 345. The power line 340 connects the two power line couplers 341 and 345. The power line 340 is shown to be co-axial cables that each includes a line core 342 and a line shield 343. Transmission line types other than the co-axial cable may also be viable, e.g., a twisted pair line. The power line shield 343 is connected to the ground line 350 with one or a number of shield grounding lines 344 respectively. This grounding is desirable, but it is also optional.
For the clock line 360,
The pulsed light clock signal is transmitted from the light source 366 through the module-side clock coupler 365 to an optical fiber 362, which is further transmitted through the optical fiber clock line 362 and the sensor-side clock coupler 365 into the image sensor 310. The optic fiber clock line 362 connects the two clock line couplers 361 and 365. It includes a flexible, transparent fiber made of a glass (silica) core, and is wrapped by a transparent cladding material that has a lower index of refraction than that of the glass core. The optic fiber clock line 362 is not made of an electric conductor, and does not function like a conventional electrical transmission line.
Inside the image sensor 310, the pulsed light clock signal is converted into an electrical (voltage) clock signal by an opto-electric conversion unit, such as a photodiode 367. The converted voltage clock signal is then transmitted through a clock signal conveyance path 369 to reach an opto-electric supporting block 368 to be further refined. For example, the supporting block 368 may include a phase locked loop (PLL) circuitry that refines the shape of the voltage clock signal to produce a cleaner and more uniform square waveform. The final voltage clock signal, either with or without the aforementioned refinement, supports a necessary part for the timing operation to drive the sequential logic circuitry of the image sensor system 300.
In another example, the data/control signal line 330 may also be based on fiber optics instead of the conventional conductor based transmission line. In such an example, the clock line 360 may be either based on fiber optics or conventional transmission line. Also in such an example, there are opto-electric conversion units (not shown) that are in either or both of the supporting module 370 and the image sensor 310 to convert the data/control signals first from electrical to optical form, and then from optical to electrical form.
It is appreciated that both the clock line 360 and the data/control line 330 are about two meters or less. This is the conventional length of an endoscope line. For the ultra-small image sensor 310, this relatively short length contributes to the clock-related noise. Implementing these lines with fiber optics solves the noise problem without negatively affecting the utility of the endoscope system 300 (e.g., reduction of utility associated with shortening the transmission lines).
Third Image Sensor System Embodiment
The image sensor system 300 shown in
Also shown in
Also shown is a power line 540 connected to the peripheral region of supporting circuitry 420. The power line 540 is similar to the power line 340 as previously disclosed in
In
A number of optical illumination fibers 570 are connected to the fiber optic peripheral region 440 at one end. At the other end, these optical illumination fibers 570 are connected to light sources, e.g., LEDs (not shown). This design functions to provide illumination for the ultra-small image sensor system package 500. The optical illumination fibers 570 may have a diameter of about 9 to 60 micrometers.
In another example, the data/control signal line 530 may also be based on fiber optics instead of the conventional conductor based transmission line. In such an example, the clock line 560 may be either based on fiber optics or conventional transmission line. Also in such an example, there are opto-electric conversion units (not shown) that are in either or both of the supporting module 370 (see
The abovementioned examples disclose the pixel array 410 in the same plane as the supporting circuitry 420. In an alternative example, the pixel array 410 and the supporting circuitry 420 are stacked in order to reduce the image sensor footprint. More specifically, the supporting circuitry 420 positioned at and couple to the backside of the pixel array 410. The four transmission lines are still connected to the supporting circuitry 420 as previously disclosed.
The above description of illustrated examples of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific examples of the invention are described herein for illustrative purposes, various modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.
These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific examples disclosed in the specification. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.
