MEMS Microphone Interfaces

The DCC-1448 is a research-grade interface for measuring and characterizing MEMS (Micro-Electro-Mechanical-Systems) microphones and other devices with a 1-bit PDM (Pulse Density Modulation) output. Used in conjunction with an audio test system such as SoundCheck®, it forms a complete solution for the quantitative test and measurement of MEMS digital microphones.

In addition to converting the MEMS microphone’s 1-bit PDM output to a 24-bit, 48kHz PCM signal, it also includes features to measure characteristics unique to MEMS microphones. These include a programmable clock for measuring performance relative to sample rate, a programmable power supply for measuring performance relative to supply voltage and a power supply rejection impairment generator for measuring power supply rejection ratio (PSRR). The instrument is acoustically silent and can therefore be used inside an anechoic chamber, a useful feature since MEMS microphones can only drive a short cable.

Features include:

• Control and configuration within SoundCheck, via USB, or using front panel
• Straightforward operation – the data input, clock, Vdd, and ground interface are on the front panel, and the rear panel contains USB and SPIDIF interfaces for connection to the computer’s audio interface
• Simultaneous SPDIF and USB digital audio output are compatible with most test equipment with digital audio inputs and both Mac and Windows computers.
• Programmable clock typically operates as the master, but can also operate in slave mode (e.g. for measuring performance of a PDM signal generator, synching multiple microphones in an array, or where use of an external clock is preferred)
• Conversion occurs entirely in the digital domain
• Can interface with two microphones simultaneously. This is useful for testing finished product that contains multiple microphones or for characterizing matched pairs. When using two microphones all connections are shared, including the data line; one microphone transmits data on rising edge of the clock pulse and the other on the falling edge of the clock pulse. Internally to the instrument the decoded data is sent to the left and right channels of the SPDIF and USB outputs. When using two microphones the L/R selection line of one microphone is tied to ground and the other is tied to Vdd.

The PQC-3048 MEMS digital microphone interface is designed for high volume production line testing of MEMS microphones. It converts, in the digital domain, the 1-bit audio data returned by the device under test to 24 bit PCM audio at 48kHz sample rate and supplies the required clock signal and DC power for testing.

Features include:

• Control from within SoundCheck or via USB virtual com port using a command line utility
• Just two connectors: USB for power and control, and a pluggable phoenix connector to interface with the device under test
• Rugged and compact
• Simple to use with minimal potential for incorrect operation
• 2 microphones can be connected simultaneously, and multiple units can be connected to the same computer for simultaneous testing of multiple devices
• Uses the same 1-bit PDM to multi-bit PCM conversion algorithm as the DCC-1448 MEMS interface, ensuring that measurements made with one can be reproduced with the other
  Low cost – less than half the price of the DCC-1448