MIPI Camera Interface Specifications

 

The Camera Working Group released the CSI-2 v1.0 specification in 2005. A second phase addressed an updated D-PHY specification and JEDEC interleaving.

Currently, the group is developing CSI-3.

Specifications are available to MIPI members only. For more information on joining MIPI, please go to Join MIPI.

• Camera Serial Interface CSI-2 Active
• Camera Parallel Interface Legacy
• Camera Serial Interface CSI-1 Legacy

MIPI Alliance Standard for Camera Serial Interface CSI-2

 

MIPI Alliance Standard for Camera Serial Interface CSI-2

Purpose

Demand for increasingly higher image resolutions is pushing the bandwidth capacity of existing host processor-to-camera sensor interfaces. Common parallel interfaces are difficult to expand, require many interconnects and consume relatively large amounts of power. Emerging serial interfaces address many of the shortcomings of parallel interfaces while introducing their own problems. Incompatible, proprietary interfaces prevent devices from different manufacturers from working together. This can raise system costs and reduce system reliability by requiring “hacks” to force the devices to interoperate. The lack of a clear industry standard can slow innovation and inhibit new product market entry. CSI-2 provides the mobile industry a standard, robust, scalable, low-power, high-speed, cost-effective interface that supports a wide range of imaging solutions for mobile devices.

Scope

The Camera Serial Interface 2 specification defines an interface between a peripheral device (camera) and a host processor (baseband, application engine). The purpose of this specification is to identify a standard interface between a camera and a host processor for mobile device applications.

A host processor in this specification means the hardware and software that performs essential core functions for telecommunication or application tasks. The engine of a mobile terminal includes hardware and the functions, which enable the basic operation of the mobile terminal. These include, for example, the printed circuit boards, RF components, basic electronics, and basic software, such as the digital signal processing software.

Overview of CSI-2

The CSI-2 specification defines standard data transmission and control interfaces between transmitter and receiver. Data transmission interface (referred as CSI-2) is unidirectional differential serial interface with data and clock signals; the physical layer of this interface is the MIPI Alliance Standard for D-PHY [2].

Figure 1 illustrates connections between CSI-2 transmitter and receiver, which typically are a camera module and a receiver module, part of the mobile phone engine.

The control interface (referred as CCI) is a bi-directional control interface compatible with I2C standard.

 

 

Camera Parallel Interface

Introduction

The Camera Parallel Interface (CPI) is a parallel interface between a digital camera module and a mobile phone engine. This document specifies the requirements on the application processor engine (APE) and on the image sensor in order to allow the interfacing of the two components.

Overview

The Camera Parallel Interface (CPI) shall implement a 8-bit parallel link from image sensor to APE.

 

Camera Serial Interface

Introduction

The Camera Serial Interface (CSI) is a serial interface between digital camera module and mobile phone engine. The purpose of this document is to specify a standard interface between camera and phone engine. The mobile phone engine in this document means the hardware and software that performs essential core functions for telecommunication or application tasks. The engine of a mobile terminal includes hardware and the functions, which enable the basic operation of the mobile terminal. These include, for example, the printed circuit boards, RF components, basic electronics, and basic software, such as the digital signal processing software.

Overview

The interface between CSI transmitter and receiver consists of data transfer and control interface. The data transfer interface (referred as CSI in this document) is a unidirectional differential serial interface with data and clock signals. Figure 1 illustrates the connection between CSI transmitter and receiver, which typically are a camera module and a receiver module, part of the mobile phone engine.

The control interface (referred as CCI) is a bi-directional control interface compatible with I2C standard.

The physical layer of CSI is based on signaling scheme called SubLVDS, which is current mode differential low voltage signaling method modified from the IEEE 1596.3 LVDS standard for reduced power consumption. Electrical specifications for the SubLVDS I/O’s can be found from chapter 10. The use of SubLVDS enables the use of high data rates with low EMI with maximum transfer capacity of 208 Mbps. Thus transferring SVGA images (800 x 600 pixels) in YUV420 format at 30 fps is possible.

Transmission clock rate may vary between 1 MHz to 208 MHz. The maximum clock frequency of CSI should be chosen to be lowest possible for the application / transmitting device in question. It is recommended that CSI transmission clock is generated from host system clock using PLL or clock doubler. This simplifies greatly EMC design. Additional oscillators should be avoided in the camera module.

The CSI transmitter provides the data-qualifying clock to the CSI receiver. The transmission clock rate in practice can vary depending on transmitter implementation. The synchronization to receivers internal clock domain has to be handled inside the receiver. For example, a transmitter may use 13 MHz transmission clock for some type of data and 104 MHz clock for some other type of data. The principle of receiver operation is illustrated in Figure 2.