Product description

The CMX655D is an ultra-low power voice codec targeted at digital voice and sensor applications that require the lowest possible power consumption, including battery powered and small form-factor applications.

Traditionally voice codecs have interfaced to electret microphones and speakers providing A to D and D to A functions, using precision oversampling data converters. Recent advances in microphone design using MEMS techniques are now changing this, along with higher efficiency speaker driver architectures such as Class D topologies. Both of these advances enable significant reductions in power consumption which is needed to address new applications such as voice control, that require always-on operation. Such applications that are often battery powered, driving the need for ultra-low power consumption.

The CMX655D addresses these needs, providing an update to the traditional voice codec, that is both very low power and small in size. Microphone interfaces connect single or dual MEMS microphones to the device, with parallel processing of each data stream to maintain phase alignment between the two channels.

In the reverse channel, digital voice data drives a Class D speaker driver, also featuring programmable filtering and digital gain control. This architecture operates with much higher efficiency than conventional speaker drivers. An additional low level output is also provided.

The device interfaces via standard serial busses that are commonly found on many microcontrollers, DSPs and low cost single chip radio transceivers.

The CMX655D is available in a small VQFN-24 package and supported by a range of development tools, including the EV6550D and EV6550DHAT evaluation kits.

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Devices are available through our distributors below:


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  • Digital microphone MEMS support
  • High efficiency Class-D speaker driver
  • Low power consumption
  • 16 bit audio data
  • Supports conventional telephony and HD voice (300Hz – 3.4kHz and 50Hz – 7kHz bandwidths)
  • Supports audio bandwidths up to 21kHz
  • Supports 8/16/32/48 ksps sample rates
  • Flexible serial audio interface
  • SPI™/TWI control interface
  • Small 24-lead VQFN Package
  • 1.8 – 3.6V supply


  • Security alarm panels
  • Glass break detection
  • Intercom and access systems
  • Mobile radio and accessories
  • Wired telephony
  • Voice controlled equipment

Power supply requirement

  • 1.8 – 3.6V supply

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Design resources



The PE0003 Evaluation Kit Interface Card is a global interface system for use with evaluation kits for CML’s new generation ICs, including FirmASIC™ based products. This greatly simplifies the approach to the evaluation and design-in process. Link to:


The EV6550D Evaluation Kit is designed to assist in the evaluation and application development of the CMX655D. The EV6550D is designed to interface with MEMS (Micro-Electro Mechanical System) microphone evaluation boards.


EV6550_User Manual

Knowledge Base

EV6550D High Resolution Schematics. Version B03. – Please register or login to download

EV6550D High Resolution PCB Overlay. Version B01. – Please register or login to download

EV6550D Gerbers. Version B01. – Please register or login to download

EV6550D GUI. A Windows PC GUI for configuring and using the EV6550D. A PE0003 Evaluation Kit Interface Card is required to use this GUI. Version 1.2. – Please register or login to download

EV6550D BoM. Version B03 – Please register or login to download



The EV6550DHAT brings the benefits of MEMS (Micro-Electro Mechanical System) microphone technology and the CMX655D voice codec to the Raspberry Pi. This is achieved through the use of a standard Hardware on Top (HAT) design and supporting “C” based firmware and GUI (Graphical User Interface). Link to:

Package: Q6

24-pin VQFN

VQFN Design Guidance Notes

VQFN Design Guidance Notes

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