Design Resources


Q, Are the CMX994A, CMX994E and CMX994G devices pin compatible with the CMX994 in my digital radio?

A, Yes all four devices are pin and function compatible.  However, if the CMX994A, CMX994E or CMX994G are to be fitted into an existing CMX994 design, it is recommended that the new extended DC Offset register is used.

There are additional benefits in adopting the CMX994A, CMX994E and CMX995G they include additional low power operating modes, enhanced mixer IM capability and guaranteed 30MHz operation, these are illustrated below.  A means of confirming device type by a software read is also shown.

Register Name   Register bit Name CMX994 CMX994A CMX994E CMX994G Notes
Options Control - $15
Read from - $E5
  b7 IP3X x x Enhanced Mixer Intermodulation Power consumption increase by 10mA typ
  b3 PDQ x Power down entire Q receive path. I enabled 9mA typ saved
  b2 PDI x Power down entire I receive path, Q enabled 9mA typ saved
  b1..0 PHCON/PHOFF x LO Phase Correction power down bits 14mA typ saved
Extended Rx Offset - $17
Read from - $E7
  b13..8 QDC5..QDC0 x Q path extended DC offset correction  Compensation range increased from +-175mV to +-775mV in 25mV steps
  b5..0 IDC5..IDC0 x I path extended DC offset correction
Guaranteed 30MHz Operation   x x x x x Yes IP3, Image Rejection and IQ Balance performance at 30MHz
PLL M Divider - $D2  Read only.   b4,b2 ID1, ID2 00 01 10 10 Device identification bits; 11 is reserved.


Q.   Adjacent channel performance is not as good as I had expected even when applying large DC offset compensation on an unmodified EV994AE Evaluation Kit.

A.  For optimal performance the CMX994A/E PLL frequency should be centred on the wanted channel.  If it is not, then issues relating to DC Offsets and Adjacent Channel Performance will be encountered.  This is documented on the EV9942AE User Manual, section 6.5.2. Receiver Operation.

The 19.2 MHz reference for the CMX994A/E PLL is sourced from a Golledge GTXO-83 VCTCXO as shown below.

To operate within the ppm quoted frequency limits the GTXO-83 should be biased to 1.5V as a Vcc of 3V is used. As can be seen from the EV9942AE schematic extract above the biasing of the ADJ input pin is set by two resistors, R18 and R21.  This is correct for a supply voltage of 3V as R18 and R21 set the bias voltage to 3 / 2 = 1.5V.  However, as the EV994AE default supply is 3.3V therefore the resistors R18 and R21 will set the bias voltage to 1.65V, outside of the quoted specifications.

Therefore, for best performance using a 3.3V supply, R18 and R21 should be replaced with 8K87@1% and 10K7@1% resistors giving an ADJ bias of 1.496V, bringing the reference frequency into specification.   This results in a smaller DC offset that may be removed by using the CMX994AE Receive Offset Register.

Frequency Estimation for a VCO using a Negative Resistance Amplifier

Application Note describing how to estimate the operating frequency of VCO designs using a negative resistance amplifier. An Excel spreadsheet that automates the calculation is available below.


Excel Spreadsheet - Frequency Estimation for a VCO using a Negative Resistance Amplifier

An Excel spreadsheet that calculates the operating frequency of VCO designs using a negative resistance amplifier. An Application Note describing the process is available above.


CMX994/A/E Interference Immunity

Through clarification of blocking and second order intermodulation performance, together with empirical measurement, this app note illustrates the excellent characteristics of the CMX994/CMX99A/CMX994E marking its suitability for professional radio designs.


CMX994A / CMX994E 400MHz to 470MHz Operation

An Application Note demonstrating through the use of a simple RF matching circuit for the CMX994A and CMX994E devices in 400MHz to 470MHz band applications. Comparative measurements are made with the existing EV9942A/E and DE9945A Evaluation Boards throughout and results provided.


CMX994/A/E LNA Performance and Applications

An application note that describes the performance characteristics of the CMX994’s LNA and the benefits of this device for typical PMR radio designs.


CMX994 - Demonstration Video Scripts

These scripts are used in the "CMX994 Demonstration" video. The scripts guide the user through Tx/Rx frequency trimming, Rx I/Q DC offset calibration, Rx Equalizer training, Tx I/Q DC offset calibration, and formatted data transfer.


DE9941A The DE9941A is a credit-card sized, fully functional, UHF wireless data modem using the CMX994E Direct Conversion Receiver, the CMX998 Cartesian Feedback Loop Transmitter and the CMX7364 High Performance Multi-mode Wireless Data Modem. Full design data and test scripts are available to download from the DE9941A Product Page. DE9941A_Product_Page
EV9942A/9942E Two versions of the Evaluation Kit are available allowing the user to investigate all aspects of the chosen CMX994, high-performance direct conversion receiver. A common PC-based application identifies the CMX994 version and starts an interactive GUI for configuration and control. A separate hi-res schematic is available for both versions of the EV9942. EV9942_Product_Preview


EV9942 User_Manual

C-BUS Guides

Guides to operation and interfacing


EV9942 Evaluation Software

A common GUI-based application for the EV9942/EV9942A/EV9942E Evaluation Kits. A PE0003 Universal Interface Card is required to use this application. Version 4.1


EV9942 Quick Start

A simple guide to help users get started evaluating the EV9942, EV9942A and EV9942E Evaluation Kits. Ver.2


EV9942A Board Schematics

EV9942A Board high-resolution schematic. Ver.A03


EV9942E Board Schematics

EV9942E Board high-resolution schematic. Ver.A02


PE0003 Driver

PE0003 USB driver for Windows. Version 1.0



EV9942A Board BOM Ver.A03



EV9942A Board BOM Ver.A02


Package: Q4

40-pin VQFN


VQFN Design Guidance Notes

VQFN Design Guidance Notes


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