Low-Voltage 96 dB Snapshot CMOS Image Sensor with 4.5 nW Power Dissipation per Pixel

Abstract

Modern “smart” CMOS sensors have penetrated into various applications, such as surveillance systems, bio-medical applications, digital cameras, cellular phones and many others. Reducing the power of these sensors continuously challenges designers. In this paper, a low power global shutter CMOS image sensor with Wide Dynamic Range (WDR) ability is presented. This sensor features several power reduction techniques, including a dual voltage supply, a selective power down, transistors with different threshold voltages, a non-rationed logic, and a low voltage static memory. A combination of all these approaches has enabled the design of the low voltage “smart” image sensor, which is capable of reaching a remarkable dynamic range, while consuming very low power. The proposed power-saving solutions have allowed the maintenance of the standard architecture of the sensor, reducing both the time and the cost of the design. In order to maintain the image quality, a relation between the sensor performance and power has been analyzed and a mathematical model, describing the sensor Signal to Noise Ratio (SNR) and Dynamic Range (DR) as a function of the power supplies, is proposed. The described sensor was implemented in a 0.18 um CMOS process and successfully tested in the laboratory. An SNR of 48 dB and DR of 96 dB were achieved with a power dissipation of 4.5 nW per pixel.

Analog Encoding Voltage—A Key to Ultra-Wide Dynamic Range and Low Power CMOS Image Sensor

“…The charge transfer from the PPD is bidirectional, similar to [25]. In this way, we can deliberately dump the generated charge to drain the photo-diode through M 1 or we can transfer the charge for further processing to C s through M 2 .…”

“…Based on these simulations, we have concluded that the two presented designs consume power of 2.5 nW and 5.4 nW, respectively. Taking into account the anticipated extraordinary DR extension they provide, we have found that the power budget is low and definitely appropriate to the state-of-the art CMOS image sensors [25]. To summarize the anticipated performance of the proposed designs, we provide Table 1, where different state-of-the art WDR solutions are compared with respect to several key attributes such as fabrication technology, WDR technique (WDR T.), pixel size, fill factor (FF), DR, SNR, power per pixel (PPX), and frame rate (FR).…”