Application area for MIPI includes many domains, In this paper we focused on Chip-to-Chip Inter Process Communications which includes two main protocols LOW LATENCY AND DIGRF.
- MIPI DigRF: DigRF is a high-speed digital interface standard defined and supported by the Mobile Industry Processor Interface (MIPI) Alliance (www.mipi.org). It is used primarily in between the RF transceiver IC and the baseband (BB) IC in a mobile handset. It provides a standard way to transmit I/Q data between the RF transceiver and the BB chip. The receiver circuits generate the I and Q signals from the radio signal. These are digitized and otherwise processed and sent to the BB circuits for further processing. In the transmit mode, the BB chip creates the digital versions of the I and Q signals and sends them to the RF chip over the interface. The RF chip performs digital-to-analog conversion to create the analog signals that become the radio signal to be transmitted. In the past, a variety of RF and BB chips generated both digital and analog I/Q signals. There was no standard approach, meaning designers had to add extra circuits to make conversions as required to allow the two chips to talk to one another. The DigRF interface standardizes digital transfers. The digital interface is basically a serial data bus with six paths—one for receive (Rx) I/Q data, one for transmit (Tx) data, one for a clock signal, and another for a clock enable. The Rx and Tx paths are differential low-voltage differential signalling (LVDS). In the new version 4, the data rate is 1.5 Gbits/s. That speed is needed to support the newer Long-Term Evolution and WiMAX standards that also use multiple-input multiple-output (MIMO). The older version 3 transmitted at a 312-Mbit/s rate. MIPI defines a packet-based protocol that transmits the data as well as control information. Control packets send control signals between the RF and BB chips. Data packets send data in alternate I and Q words using 8B/10B FEC encoding. When MIMO is used, multiple I/Q words must be sent interleaved. The protocol overhead is typically 20% of the serial data. It is designed to provide a convenient approach for integrating components and meeting the data-intensive needs of 4G LTE air interfaces that require high channel bandwidth. It is a low-complexity solution for complex implementations that typically require multi-mode, multi-band operation. It natively handles MIMO configurations, receive diversity and carrier aggregation. In addition to LTE, it supports HSPA+, 3.5G and 2.5G air interfaces. MIPI DigRF is a high-level interface that operates on the MIPI M-PHY physical layer, enabling a single link between the baseband and RFIC[5].