Pre-Production
WM8904
ELECTRICAL CHARACTERISTICS
TERMINOLOGY
1. Signal-to-Noise Ratio (dB) – SNR is the difference in level between a full scale output signal and the device output
noise with no signal applied, measured over a bandwidth of 20Hz to 20kHz. This ratio is also called idle channel noise.
(No Auto-zero or Automute function is employed).
2. Total Harmonic Distortion (dB) – THD is the difference in level between a 1kHz full scale sinewave output signal and
the first seven harmonics of the output signal. The amplitude of the fundamental frequency of the output signal is
compared to the RMS value of the next seven harmonics and expressed as a ratio.
3. Total Harmonic Distortion + Noise (dB) – THD+N is the difference in level between a 1kHz full scale sine wave output
signal and all noise and distortion products in the audio band. The amplitude of the fundamental reference frequency of
the output signal is compared to the RMS value of all other noise and distortion products and expressed as a ratio.
4. Channel Separation (dB) – is a measure of the coupling between left and right channels. A full scale signal is applied
to the left channel only, the right channel amplitude is measured. Then a full scale signal is applied to the right channel
only and the left channel amplitude is measured. The worst case channel separation is quoted as a ratio.
5. Multi-Path Crosstalk (dB) – is the measured signal level in the idle path at the test signal frequency relative to the
signal level at the output of the active path. The active path is configured and supplied with an appropriate input signal
to drive a full scale output, with signal measured at the output of the specified idle path.
6. Channel Level Matching (dB) – measures the difference in gain between the left and the right channels.
7. Power Supply Rejection Ratio (dB) – PSRR is a measure of ripple attenuation between the power supply pin and an
output path. With the signal path idle, a small signal sine wave is summed onto the power supply rail, The amplitude of
the sine wave is measured at the output port and expressed as a ratio.
8. All performance measurements carried out with 20kHz AES17 low pass filter for distortion measurements, and an
A-weighted filter for noise measurement. Failure to use such a filter will result in higher THD and lower SNR and
Dynamic Range readings than are found in the Electrical Characteristics. The low pass filter removes out of band
noise; although it is not audible it may affect dynamic specification values.
COMMON TEST CONDITIONS
Unless otherwise stated, the following test conditions apply throughout the following sections:
DCVDD = 1.0V
DBVDD = 1.8V
AVDD = CPVDD =1.8V
Ambient temperature = +25°C
Audio signal: 1kHz sine wave, sampled at 48kHz with 24-bit data resolution
SYSCLK_SRC = 0 (system clock comes direct from MCLK, not from FLL).
Additional, specific test conditions are given within the relevant sections below.
PP, Rev 3.3, September 2012
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
