D2RF Digital to RF Direct Converters

Objectives

The objective of this activity is to develop a breadboard device, in whatever technology deemed appropriate after a thorough analysis of available options, that demonstrates the feasibility of digital signal processor based equipment to directly output an RF signal.
The targeted improvement is to eliminate the baseband (BB) or intermediate frequency (IF) to RF converters required to support digitally processed payloads, and digital modulators, thus saving mass, power and cost.
 
The translation from the digital processor’s output to either C-, Ku-, or Ka-band generates, apart from the envisaged RF output, a number of unwanted signals such as the image(s), local oscillator (LO) or carrier leakage, close-by spurious mixing products (e.g. LO±2IF, LO±3IF,..), harmonics and folded-down spurs.
It is expected that the contractor implements techniques (e.g. adaptive biasing, multi-order cancellation technology, polyphase filters, multipath/multi-order cancellation, predistortion linearization, linear interpolation,…) for suppressing these unwanted outputs to levels that are acceptable for the transmit RF section of the payload.

Challenges

Main challenges are; Dynamic range, power consumption, reference clock generation and input data bandwidth. Associated challenges due to limited dynamic range are; SFDR, NPR and accumulated phase-noise due to noise floor. Power consumption is a result of the extensive input data rate which is the major draw-back of the current available RF DACs.

Benefits

A direct sampling DAC could generate multiple frequency bands simultaneously if desired. The main benefit though is the flexibility (in what frequency bands to use and sub-channel bandwidth) and the high order of integration. If the overall dynamic range of the DAC is large enough, output power control per sub-channel is also achievable. The oversampling gain also works in favour for multi-Giga-sample DACs by increasing the effective-number-of-bits.

Features

Targeted accumulated usable bandwidth with current technology is set to 500 MHz bandwidth, distributed at any desired frequency (within assigned band). This limitation comes from the available dynamic range together with regulatory requirements. Usage of up to Ka-band is targeted, enabled by a sample rate of 67 Gsps, low intrinsic jitter and high analogue bandwidth.

System Architecture

The system architecture is based on an evaluation platform from a vendor supplying these types of components. The transmitter line-up is analysed and characterized but not build. The system setup aims to enable verification of a multiple set of user cases proving, when verified, the usability of the RF DAC component with the limitations of the current available technology.

Plan

This study has three phases:

  • Requirements Establishment
  • Technology Selection and Design
  • Technology Demonstration

Current status

Presently the Requirements have been consolidated and possible technologies have been compared for technology selection on PM1 after Requirements Establishment phase, going a little ahead of schedule and including part of the next phase. The plan is to be able to procure the selected device (and board) and prepare for the Technology Demonstration.

Contacts

ESA Contacts

Status date

Monday, August 28, 2017 - 11:01