WM8978 查看數據表（PDF） - Wolfson Microelectronics plc

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WM8978

Stereo CODEC With Speaker Driver

Wolfson Microelectronics plc 

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WM8978

TERMINOLOGY

1. Input level to RIP and LIP in pseudo-differential configurations is limited to a maximum of -3dB or THD+N

performance will be reduced.

2. Note when BEEP path is not enabled then AUXL and AUXR have the same input impedances.

3. Hold Time is the length of time between a signal detected being too quiet and beginning to ramp up the gain. It does

not apply to ramping down the gain when the signal is too loud, which happens without a delay.

4. Ramp-up and Ramp-Down times are defined as the time it takes for the PGA to sweep across 90% of its gain range.

5. All hold, ramp-up and ramp-down times scale proportionally with MCLK

6. Signal-to-noise ratio (dB) – SNR is a measure of the difference in level between the full scale output and the output

with no signal applied. (No Auto-zero or Automute function is employed in achieving these results).

7. 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).

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

9. 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.

10. The maximum output voltage can be limited by the speaker power supply. If OUT3BOOST, OUT4BOOST or

SPKBOOST is set then SPKVDD should be 1.5xAVDD to prevent clipping taking place in the output stage (when

PGA gains are set to 0dB).

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PP Rev 1.7 January 2005

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