WM8940
Pre-Production
TERMINOLOGY
1. Full-scale input and output levels scale in relation to AVDD or AVDD2 depending upon the input or output used. For
example, when AVDD = 3.3V, 0dBFS = 1Vrms (0dBV). When AVDD < 3.3V the absolute level of 0dBFS will decrease
with a linear relationship to AVDD.
2. Input level to RIP and LIP in differential configurations is limited to a maximum of -3dB or performance will be
reduced.
3. Signal-to-noise ratio (dB) – SNR is the difference in level between a reference full scale output signal and the device
output with no signal applied. This ratio is also called idle channel noise. (No Auto-zero or Automute function is
employed in achieving these results).
4. Total Harmonic Distortion (dB) – THD is the difference in level between a reference output signal and the first seven
harmonics of that signal. The reference output signal need not be at full scale amplitude; THD is typically measured
using an output power of 20mW into a 16ohm load, corresponding to a reference signal level of -5dB. However the
stated test conditions include input signal level, signal gain settings, output load characteristics and power supply
voltages To calculate the ratio, the fundamental frequency of the output signal is notched out and an RMS value of
the next seven harmonics is calculated.
5. THD is the difference in level between a reference output signal and the first seven harmonics of the output signal. To
calculate the ratio, the fundamental frequency of the output signal is notched out and an RMS value of the next seven
harmonics is calculated.
6. Total Harmonic Distortion plus Noise (dB) – THD+N is the difference in level between a reference output signal and
the sum of the harmonics, wide-band noise and interference on the output signal. To calculate the ratio, the
fundamental frequency of the output signal is notched out and an RMS value of the total harmonics, wide-band noise
and interference is calculated.
7. 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
Pre-Production, Rev 3.0, February 2007
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
