Analog Control Interface WG eTrak® Specification

MIPI® Alliance Defines Analog Reference Interface for Envelope Tracking

New eTrak® Specification Addresses Mobile System RF Power Efficiency 

Mobile phone transmitters are one of the three biggest power consumers in today’s mobile systems. By integrating eTrak into RF modem chipsets and Envelope Tracking Power Supplies (ETPS), the specification allows modem ICs to control the supply voltage of RF power amplifiers, which improves the efficiency of the transmitter.

The majority of today’s methods are proprietary or de-facto standards that are not utilized industry-wide. Previous fixed proprietary alternatives did not allow manufacturers the benefits of an industry standard solution including improved efficiency and lower costs. The eTrak Specification was developed to address current and future market needs.

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


The Analog Reference Interface for Envelope Tracking (abbreviated as eTrak) Specification v1.0 has been defined to support the deployment of Envelope Tracking (ET). Envelope tracking is a leading method of increasing Power Amplifier (PA) efficiency at high output power levels when transmitting at a high data rate with advanced modulation as defined in later releases of the 3GPP cellular standards (e.g., LTE, HSUPA and TD-SCDMA). 

The eTrak Specification has been defined to offer a standardized interface in between the cellular transmitter (transmitter could be either in the RFIC or in the BBIC) and the ET Power Supply in order to convey an analog representation of the desired power supply voltage to the ETPS.



The eTrak 1.0 Specification describes a high speed analog differential interface to be used between a transmitter and the ETPS to support envelope tracking. This interface specification applies to cellular transmitter architectures in general and specifically HSUPA and LTE transmitters supporting up to LTE 20 MHz channel bandwidth.

The control interface between the transmitter and the ETPS is out of scope. It is addressed by the MIPI RFFE Specification, or a similar interface. The interface between the ETPS and different PA devices is also outside the scope of this document.

The eTrak 1.0 Specification document does not describe the implementation of an envelope tracking system. It ensures interoperability between the transmitter and the ETPS when both devices are compliant with this specification, but it does not limit device or system implementation. 


The purpose of the standard is to describe the electrical characteristics of the eTrak interface with sufficient detail to allow physical implementation for 3G/4G systems as specified by 3GPP standards.

Every effort has been made to retain flexibility where this does not compromise compatibility or cost, thus leaving design choices to the BBIC/RFIC and ETPS vendors.


Application Note

The MIPI Alliance Application Note for Analog Reference Interface for Envelope Tracking (eTrakSM)  v1.0 is currently being developed and is expected to be released to members by the end of 2013. This document is a companion document to the actual eTrak Specification and describes the derivation of each individual item in the eTrak Specification. It addresses the complete ET system, but only at a level of detail sufficient to derive a numerical value for key parameters of the interface. In doing this the application note discusses various potential implementation options of ET system components, but the application note is not intended to dictate or recommend any particular implementation.


Conformance Test Suite

The MIPI Alliance Conformance Test Suite for Analog Reference Interface for Envelope Tracking (eTrakSM) v1.0 is currently being developed and is expected to be released to members Q1 2014.  This Conformance Test Suite is being developed in an effort to improve the interoperability of MIPI Specification-based products. This document defines a set of conformance or interoperability tests whereby a product can be tested against other implementations of a common Specification.