Prophesee and Sony develop stacked ‘event-based’ vision sensor

21 Feb 2020

Features “industry’s smallest pixels and highest HDR performance” among stacked event-based vision sensors.

Sony and France-based tech firm Prophesee (formerly Chroncam, which rebranded as Prophesee, two years ago) have jointly developed a “stacked event-based vision sensor” featuring what they describe as “the industry’s smallest 4.86 μm pixel size and the industry’s highest 124dB-plus HDR performance”.

The sensor is suitable for various machine vision applications, such as detecting fast moving objects in a wide range of environments and conditions. It was first presented publicly at the International Solid-State Circuits Conference (ISSCC) held in San Francisco, this week, February 16-20th.

The stacked event-based vision sensor detects changes in the luminance of each pixel asynchronously and outputs data including coordinates and time only for the pixels where a change is detected, thereby enabling high-efficiency, high-speed and low-latency data output – all despite its small size and low power consumption.

The partners say that this achievement was made possible by combining technical features of Sony’s stacked CMOS image sensor, resulting in small pixel size and excellent low light performance that are achieved by the use of Cu-Cu connection (see below), with Prophesee’s Metavision Event-based vision sensing technologies leading to fast pixel response, high temporal resolution and high throughput data readout.

Cu-Cu to you

Cu-Cu Connection Technology provides electrical continuity via connected Cu (copper) pads when stacking the back-illuminated CMOS image sensor section (upper chip) and logic circuits (lower chip).

Compared with through-silicon via (TSV) wiring, in which the connection is achieved by penetrating electrodes around the circumference of the pixel area, this method gives more freedom in design, improves productivity, allows for a more compact size, and increases performance.

Main features

• Small size and high resolution delivered by stacked Event-based vision sensor with the industry’s smallest 4.86 μm pixel size. The pixel chip (upper) and the logic chip (lower) incorporate signal processing circuits which detect changes in luminance based on an asynchronous delta modulation method are arrayed separately.
• Each pixel of the two individual chips is electrically connected using Cu-Cu connection in a stacked configuration. In addition to the small pixel size, the sensor also delivers 1/2 type, 1280 x 720 HD resolution by achieving high density integration with a fine 40nm logic process.
• While a frame-based sensor outputs entire images at fixed intervals according to the frame rate, an event-based sensor selects pixel data asynchronously using a row selection arbiter circuit. By adding time information at 1 μs precision to the pixel address where a change in luminance has occurred, event data readout with high time resolution is ensured. Furthermore, a high output event rate of 1.066Geps has been achieved by efficiently compressing the event data, i.e. luminance change polarity, time, and x/y coordinate information for each event.