CMX998 CML Microcircuits Cartesian Feed-back Loop Transmitter COMMUNICATION SEMICONDUCTORS D/998/16 May 2021 Features Applications Frequency Range 30MHz to 1GHz TETRA Terminals Wide Band Noise 148dBc/Hz TETRA 2 Terminals C-BUS (SPI compatible) Serial Interface APCO P25 Phase 2 Gain Control Aviation Systems Error Amplifier Mobile Satellite Terminals Up Converter Forward Path Linear Modulation Schemes: Down Converter for Feedback QPSK, /4-DQPSK, 8PSK, QAM, Linearisation OFDM, F4FM, etc. 360 Loop Phase Shift Control Direct Interface to CMX981, CMX980A DC Offset Measurement Output and CMX7163/CMX7164 Open Loop Function Instability Detector Flexible Digital Interface 1 Brief Description A Cartesian Loop improves the efficiency and linearity of transmitters for non-constant envelope modulation systems. The CMX998 is an integrated solution for a Cartesian Feedback Loop based linear transmitter. Acting as a direct conversion quadrature mixer from I and Q to RF output, it provides the capability to linearize 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 device operates from a single 3.3V supply over a temperature range of -40C to +85C and is available in a 64-pin VQFN (Q1) package. 2021 CML Microsystems Plc Cartesian Feed-Back Transmitter CMX998 CONTENTS Section Page 1 Brief Description ..................................................................................... 1 2 Block Diagram ......................................................................................... 3 3 Signal List ................................................................................................ 4 3.1 Signal Definitions ............................................................................. 5 4 External Components ............................................................................. 6 4.1 Power Supply Decoupling ............................................................... 6 4.2 Upconverter....................................................................................... 7 4.3 Down Converter ................................................................................ 8 4.4 Local Oscillator Input ....................................................................... 8 4.5 Instability Detector ........................................................................... 9 4.6 Error Amplifier................................................................................. 10 5 General Description .............................................................................. 11 5.1 Input Amplifiers .............................................................................. 11 5.2 Forward Path ................................................................................... 11 5.3 Feedback Path ................................................................................ 12 5.4 Local Oscillator Phase Shifting ..................................................... 12 5.5 DC Nulling ....................................................................................... 12 5.6 Instability Detector ......................................................................... 14 5.7 Reference Voltages ........................................................................ 15 5.8 RF Power Detector ......................................................................... 16 5.9 Operation over 30MHz to 100MHz ................................................. 16 6 C-BUS Interface and Register Description ......................................... 18 6.1 General Reset Command ............................................................... 20 6.2 General Control Register ............................................................... 20 6.3 Phase Control Register .................................................................. 21 6.4 Gain Control Register .................................................................... 22 6.5 Forward Path Gain Control Register ............................................ 23 6.6 Feedback Path Gain Control Register .......................................... 23 6.7 Aux Control Register ...................................................................... 24 6.8 Frequency Control Registers ........................................................ 25 7 Performance Specification ................................................................... 26 7.1 Electrical Performance ................................................................... 26 7.2 Packaging ........................................................................................ 36 2021 CML Microsystems Plc 2 D/998/16