NAU8812EVB Nuvoton Technology Corporation of America, NAU8812EVB Datasheet - Page 31

• Manufacturer Part Number: NAU8812EVB
• Description: BOARD EVAL FOR NAU8812
• Manufacturer: Nuvoton Technology Corporation of America
• Series: emPowerAudio™r

Specifications of NAU8812EVB

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

When the absolute value of the ADC output exceeds the level set by the ALC threshold, ALCSL[3:0] address (0x21),
attack mode is initiated at a rate controlled by the attack rate register ALCATK[3:0] address (0x22). The peak
detector in the ALC block loads the ADC output value when the absolute value of the ADC output exceeds the current
measured peak; otherwise, the peak decays towards zero, until a new peak has been identified. This sequence is
continuously running. If the peak is ever below the target threshold, then there is no gain decrease at the next attack
timer time; if it is ever above the target-1.5dB, then there is no gain increase at the next decay timer time.
The decay time ALCDCY[6:4] address (0x22) is the time constant used when the gain is increasing. In limiter mode,
the time constants are faster than in ALC mode.
A noise gate is used when there is no input signal or the noise level is below the noise gate threshold. The noise
gate is enabled by setting ALCNEN[3] address (0x23) to HIGH. It does not remove noise from the signal. The noise
gate threshold ALCNTH[2:0] address (0x23) is set to a desired level so when there is no signal or a very quiet signal
(pause), which is composed mostly of noise, the ALC holds the gain constant instead of amplifying the signal towards
the target threshold. The noise gate only operates in conjunction with the ALC and ONLY in Normal mode. The
noise gate flag is asserted when
Levels at the extremes of the range may cause inappropriate operation, so care should be taken when setting up the
function.
emPowerAudio
Datasheet Revision 2.0
12.4.3. Attack Time
12.4.4. Decay Times
12.4.5. Noise gate (normal mode only)
(Signal at ADC – PGA gain – MIC Boost gain) < ALCNTH (ALC Noise Gate Threshold) (dB)
™
PGA Output
PGA Input
PGA Gain
Figure 15: ALC Operation with Noise Gate disabled
Page 31 of 109
NAU8812
January 2011