PDM 16 Input Module for APx B Series Audio Analyzers
16-channel solution for MEMS microphone array testing

Pulse Density Modulation (PDM) is a one-bit, high rate data stream that conveys a signal by modulating the density of the pulses. PDM is commonly used as the digital output of MEMS (micro-electromechanical system) microphones that are, either individually or in an array, integral components in smartphones, hearing aids, mobile computing, automotive systems, smart speakers and other IOT systems.

PDM 16 is an optional input module for the modular APx Series audio analyzers. Comprised of the input module installed in the analyzer, a remote interface pod and an extension cable, the module provides sample-accurate inter-channel phase information for up to 16 channels, critical data for the creation of MEMS mic arrays. PDM 16 utilizes synchronous sampling based on a common clock, thereby assuring a clear picture of the phase relationship between channels.


 

APx500 audio measurement software displaying phase spectrum results of test board equipped with 16 MEMS microphones.

Anechoic Chamber Test Setups
The module’s remote interface pod (used in all PDM 16 configurations) and extension cable preserve PDM signal integrity, ensuring measurement system performance even when the DUT, along with the acoustically-silent pod, is in an anechoic chamber up to 10 meters from the analyzer. PDM 16 extension cables are available in 2-, 5-, or 10-meter lengths.

Built-in Power Supply
The logic level and external power supply voltage are variable in 0.1 V steps, allowing testing beyond the range of typical devices. These are set independently, with the logic level settable from 0.8 V to 3.3 V and power supply control (Vdd) adjustable from 0.0 V to 3.6 V (50 mA max).

Integrated Audio Test
As an APx module, PDM 16 is part of an integrated audio test solution, leveraging the combined power and flexibility of the APx500 audio measurement software and market-leading test hardware for signal generation and acquisition. Along with PDM 16, APx500 Series analyzers can include modules for testing components or systems that also use interfaces ranging from analog to chip-level I2S and TDM protocols, Bluetooth or HDMI. A PDM 16-equipped analyzer can even be equipped with the existing APx PDM module to add two channels of PDM output, as well as power supply rejection (PSR) and jitter measurements.

Compatibility & Requirements
The PDM 16 module is designed to operate within any of the modular APx analyzers, B Series or Legacy, including the APx525, APx526, APx582, APx585, APx586, and APx555. PDM 16 is compatible with analyzers manufactured August 2012 or later. Note: only one PDM 16 module can be installed in an analyzer, and software version 5.0.3 (or later) is required. DUT connection is via a 40 pin IDC 2.54mm (0.1”) cable header on remote pod (not included).

PDM 16 MODULE PERFORMANCE
Sample Rate Range
4 kHz to 216 kHz

Clock Range
128 kHz to 24.576 MHz

Oversampling Rate
32, 64, 128, 256

Edge Modes
Rising edge, odd channels
Falling edge, even channels

Vdd Output
0.0 to 3.6 V, 50 mA max

Interface Logic Levels
0.8 to 3.3 V

SNR
< 129 dB (20 kHz BW, unweighted)

THD+N
< -130 dB (20 kHz BW, unweighted)

Dynamic Range
< 137 dB (AES17, CCIR-RMS)

Flatness
±0.002 dB (20 Hz to 20 kHz, 32x decimation)
±0.001 dB (20 Hz to 20 kHz, 64x, 128x, 256x, 512x decimation)

Decimation Ratios
Five selectable: 32x, 64x, 128x, 256x, 512x

Interchannel Phase Alignment
All channels sampled synchronously from common clock, phase relationships between channels full maintained

Connector
Connection to DUT is via 40-pin IDC 2.54 mm (0.1″) cable header (on remote pod)

PDM 16 Input Module