Preliminary Technical Data

WM7121

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PTD, Rev 2.0, October 2012

7

APPLICATIONS INFORMATION

RECOMMENDED EXTERNAL COMPONENTS

Figure 1 WM7121 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 for further information.