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WM8782

w

PP, May 2004, Rev 1.0

7

Analogue Reference Levels

Midrail Reference Voltage

VMID

AVDD to VMID and

VMID to VREFN

–3%

AVDD/2

+3%

V

Potential Divider Resistance

50

kΩ

Buffered Reference Voltage

VREFP

–3%

AVDD/2

+3%

V

VREF source current

5

mA

VREF sink current

5

mA

Supply Current

Analogue supply current

AVDD = 5V

55

mA

Digital supply current

DVDD = 3.3V

4

mA

Power Down

0.5

mA

Notes:

1.

All performance measurements are done with a 20kHz low pass filter, and where noted an A-weight filter, except

where noted. Failure to use such a filter will result in higher THD+N and lower SNR and Dynamic Range readings than

are found in the Electrical Characteristics. The low pass filter removes out of band noise; although this is not audible,

it may affect dynamic specification values.

2.

VMID is decoupled with 10uF and 0.1uF capacitors close to the device package. Smaller capacitors may reduce

performance.

3.

This high leakage current is due to the topology of the instate pads. The pad input is connected to the midpoint of an

internal resistor string to pull input to vmid if undriven.

TERMINOLOGY

1.

Signal-to-noise ratio (dB) – Ratio of output level with 1kHz full scale input, to the output level with all zeros into the

digital input, over a 20Hz to 20kHz bandwidth. (No Auto-zero or Automute function is employed in achieving these

results).

2.

Dynamic range (dB) – DR is a measure of the difference between the highest and lowest portions of a signal.

Normally a THD+N measurement at 60dB below full scale. The measured signal is then corrected by adding the 60dB

to it. (e.g. THD+N @ -60dB= -32dB, DR= 92dB).

3.

THD+N (dB) – THD+N is a ratio, of the rms values, of (Noise + Distortion)/Signal.

4.

Channel Separation (dB) – Also known as Cross-Talk. This is a measure of the amount one channel is isolated from

the other. Normally measured by sending a full scale signal down one channel and measuring the other.