WM8783

Production Data

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PD, August 2010, Rev 4.0

14

APPLICATIONS INFORMATION

RECOMMENDED EXTERNAL COMPONENTS

AUDIO INPUT PATHS

The WM8783 provides 2 analogue audio inputs. Each of these inputs is referenced to the internal DC

reference, VMID. A DC blocking capacitor is required for each input pin. The choice of capacitor is

determined by the filter that is formed between that capacitor and the input impedance of the input

pin. The circuit is illustrated in Figure 9.

Figure 9 Audio Input Path DC Blocking Capacitor

The input impedance is noted in the “Electrical Characteristics”. It is recommended that an input

capacitor is selected such that the Fc cut-off frequency is less than 20Hz.

It is recommended that a 1

μF capacitance is used for all WM8783 input connections. Tantalum

electrolytic capacitors are particularly suitable as they offer high stability in a small package size.

See Wolfson Applications Note WAN_0176 for further guidance on the choice of capacitor types.

POWER SUPPLY DECOUPLING

Electrical coupling exists particularly in digital logic systems where switching in one sub-system

causes fluctuations on the power supply. This effect occurs because the inductance of the power

supply acts in opposition to the changes in current flow that are caused by the logic switching. The

resultant variations (or ‘spikes’) in the power supply voltage can cause malfunctions and

unintentional behavior in other components. A decoupling (or ‘bypass’) capacitor can be used as an

energy storage component which will provide power to the decoupled circuit for the duration of these

power supply variations, protecting it from malfunctions that could otherwise arise.

Coupling also occurs in a lower frequency form when ripple is present on the power supply rail

caused by changes in the load current or by limitations of the power supply regulation method. In

audio components such as the WM8783, these variations can alter the performance of the signal

path, leading to degradation in signal quality. A decoupling (or ‘bypass’) capacitor can be used to

filter these effects, by presenting the ripple voltage with a low impedance path that does not affect

the circuit to be decoupled.

These coupling effects are addressed by placing a capacitor between the supply rail and the

corresponding ground reference. In the case of systems comprising multiple power supply rails,

decoupling should be provided on each rail.

The recommended power supply decoupling capacitors for WM8783 are listed below in Table 2.

POWER SUPPLY

DECOUPLING CAPACITOR

AVDD

4.7

μF ceramic

VMIDC

4.7

μF ceramic

Table 2 Power Supply Decoupling Capacitors

All decoupling capacitors should be placed as close as possible to the WM8783 device.