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Document overview
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Technical content
Features
- WM7121P MEMS microphone
- Flexible PCB for full acoustic validation — Pressure field —F r e e f i e l d
- Plug-and-play interface to smart codec main board — Functional test — Full signal path setup with smart codec — System development and prototyping — Algorithm verification
Description
The CDB7121P is a flexible PCB for full electrical and acoustic validation of the WM7121P MEMS microphone. The CDB7121P is designed to connect to test equipment via on board test points or via a codec main board with mating edge connector socket. The CDB7121P is ideally suited for pressure field acoustic measurements. Furthermore, the flexible region can be trimmed to enable accurate free field measurements to be made. The CDB7121P also serves as a component and layout reference for the WM7121P.
Ordering Information
CDBWM7121-M-2 Customer Demo Board Test points Edge connector pads Power and I/O Power and I/O Trim line Acoustic port hole WM7121P CDB7121P
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1 System Overview
The CDB7121P customer demo board is a flexible PCB for evaluating the WM7121P low-profile analog silicon microphone. The following subsections describe the features of CDB7121P customer demo board in detail.
1.1 Test Points
Six test points are available to provide all the connections from WM7121P to standard test equipment for full acoustic measurement. Test points are described in Table 1-1. The operating supply voltage of WM7121P is provided in the data sheet, which is available from Cirrus website.
1.2 Edge Connector
The J1 and J2 edge connector pads provide a pluggable connection to a codec main board with compatible edge card socket. The edge connector pin-outs are described in Table 1-2 and Table 1-3.
1.3 Trim Line
To enable more accurate free field frequency responses to be obtained, the flexible region of the CDB7121P may be trimmed to reduce acoustic interactions. If required, there is a guide line on the silkscreen that can be cut along. Refer to Fig. 4-1 for further details. Table 1-1. Test Point signals Test Point Pin Direction Description TP1 VDD Supply Analog Supply TP2 OP+ Output Microphone analogue output signal TP3 NA NA Not Applicable TP4, TP5, TP6 GND Ground reference Analog GroundTable 1-2. Edge connection J1 Pin Pin Direction Description
1 OP+ Output Microphone analogue output signal
(pin 1 is marked by a small dot)
2 VDD Supply Analog supply from codec MICBIAS
3, 7 GND Ground reference Analog ground 8 — — Not applicable 4, 5, 6, 9, 10 NC — No connection Table 1-3. Edge connection J2 Pin Pin Direction Description 1,2,3,4,5,6,7,8,9,10 NC NA No Connection
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2 Quick Setup Guide
As a standalone PCB, the CDB7121P can be used in a pressure field acoustic test setup or free field acoustic test setup. It can also be connected to a compatible codec main board to enable full signal path setup within a system platform. Acoustic measurements can be obtained using a number of different methods. Typical acoustic test setups, using a comparison method, are shown in Section 2.1 and Section 2.2.
2.1 Pressure field acoustic test
Recommendations for accurate pressure field measurements are as follows:
- Ensure calibrated test equipment is used for making measurements
- Ensure CDB7121P acoustic port hole is tightly sealed within the pressure field test cavity
- Ensure CDB7121P and reference mic are placed close together with minimum placement error
- Use a suitable test microphone—a pressure field reference microphone is recommended
- Ensure the pressure field test cavity is tightly sealed
- Measurements should be performed within a quiet environment Figure 2-1. Pressure field test setup with CDB7121P Pressure Field Reference Mic Test Speaker Power Quiet Environment Sound Pressure Level Standard Test Equipment Test Point Connections Pressure Field Test Cavity CDB7121P
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2.2 Free field acoustic test
Recommendations for accurate free field measurements are as follows:
- Ensure calibrated test equipment is used for making measurements
- Ensure CDB7121P acoustic port hole and reference mic are facing to the incoming sound pressure
- Ensure CDB7121P and reference mic are placed close together with minimum placement error
- The CDB7121P may be trimmed along the ‘Trim line’ to improve accuracy
- Use a suitable test microphone—a free field reference microphone is recommended
- Measurements should be performed within an anechoic environment Figure 2-2. Free field test setup with CDB7121P Free Field Reference Mic Test Speaker Power Anechoic Chamber Sound Pressure Level Standard Test Equipment Test Point Connections CDB7121P
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3 Schematic
CON_FING_10WAY_0.8PITCH_A 1010 CON_FING_10WAY_0.8PITCH_B TP1 TP6 TP2 VDD 2GND GND OUTPUT WM7121_MIC_MS4 TP3 TP5 0.1uF TP4 TP7 TP8 TP9 TP10 TP11VDD VOUTP VDD VOUTP GND GND GND DUTVDD NA VOUTN_GND VOUTN_GND GND
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4 Layout
5 Known Issues
There are no known issues with this board.
6 Bill of Materials
7 Revision History
Figure 4-1. Top Layer + Silkscreen Figure 4-2. Bottom Layer + Silkscreen Table 6-1. Bill of Materials Item RefDes Description Manufacturer Manufact urer's Part Number
1 U1 WM7121P Bottom Port Analog Silicon Microphone Cirrus Logic WM7121PIMSE
2C 1 0 . 1 - F 0603 SMD Ceramic Capacitor 16 V X7R Phycomp 2238 786 15649 3, 4 R1, R4 0- 0603 SMD chip resistor 1% 0.063W Multicomp MC 0.063W 0603 0R
5 PCB WM7121P Top Port demo board PCB Cirrus Logic CDB71T-4B-M1
Table 7-1. Revision History Revision Changes DB1 NOV ‘16
- Initial version. Important: Please check www.Cirrus.com to confirm that you are using the latest revision of this document and to determine whether there are errata associated with this device.
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