CML - Radio Frequency - CMX998

A Cartesian Feedback Loop (CFBL) Transmitter improves the efficiency and linearity of transmitters for non-constant envelope modulation systems.

The CMX998 is an integrated solution for a linear based Cartesian Feedback Loop (CFBL) transmitter.

Acting as a direct conversion quadrature mixer from I and Q to RF output, it provides the capability to linearise the Power Amplifier (PA) via feedback from the PA's output.

Included are forward and feedback paths; local oscillator circuitry including loop phase control; an instability detector and uncommitted op-amps for input signal conditioning.

The differential inputs are ideal for direct connection to standard modems and interface ICs such as CML’s CMX7163 QAM Data Modem, CMX7164 Multi Mode Wireless Data Modem, CMX910 AIS Baseband Signal Processor, CMX981 Digital Radio Baseband Processor , CMX983 Analogue Front End (AFE) for Digital Radio and CMX7861 Programmable Baseband Interface IC.


  • Frequency Range: 30MHz to 1GHz
  • Wideband Noise: ‑148dBc/Hz
  • C-BUS (SPI Compatible) Serial Interface
  • Gain Control, Error Amplifier
  • Up-Converter Forward Path
  • Down-Converter for Feedback Linearisation
  • 360o Loop Phase Shift Control
  • DC Offset Measurement Output
  • Open-Loop Function, Instability Detector
  • Linearisation Gains of 30dB or more Achievable
  • Flexible Digital Interface


  • TETRA/TETRA2 Terminals
  • APCO P25 Phase 2
  • Software Defined Radio (SDR)
  • Aviation Systems
  • Mobile Satellite Terminals
  • Linear Modulation Schemes:

Supply Requirement:

  • 3.0 to 3.6 V power supply