WM7121P Datasheet, PDF (7/13 Pages) Wolfson Microelectronics plc – Top Port Analogue Silicon Microphone

Pre-Production
APPLICATIONS INFORMATION
RECOMMENDED EXTERNAL COMPONENTS
WM7121P, WM7121PE
Figure 1 WM7121P Recommended External Components
A DC-blocking output capacitor is required on the OUTPUT pin, as illustrated in Figure 1. A single
capacitor is required for a single-ended connection. The capacitor must be correctly selected as it
affects the cut-off frequency of the output path. A low cut-off frequency is desirable as it means there
is no significant filtering of the audio bandwidth.
The 3dB cut-off frequency of the output path is given by the equation below, where C is the output
capacitance and R is the input resistance of the other circuit.
A typical recommended configuration, with 1uF DC-blocking capacitor and 20kΩ minimum input circuit
impedance, gives a 3dB cut-off frequency of 10Hz or less. Tantalum electrolytic capacitors are
particularly suitable for the DC-blocking components as they offer high stability in a small package
size.
OPTIMISED SYSTEM RF DESIGN
For optimised RF design please refer to document WAN0278 (Recommended PCB Layout for
Microphone RF Immunity in Mobile Cell Phone Applications) for further information.
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PP, June 2014, Rev 3.0
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