NAU8812EVB Nuvoton Technology Corporation of America, NAU8812EVB Datasheet - Page 26

• 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

The digital ADC can be muted by setting “0000 0000” to ADCGAIN[7:0] address (0x0F). Any other combination
digitally attenuates the ADC output signal in the range -127dB to 0dB in 0.5dB increments].
NAU8812 has a programmable gain amplifier (PGA) which controls the gain such that the signal level of the PGA
remains substantially constant as the input signal level varies within a specified dynamic range. The PGA has two
functions


The Automatic Level Control (ALC) seeks to control the PGA gain in response to the amplitude of the input signal
such that the PGA output maintains a constant envelope. A digital peak detector monitors the input signal amplitude
and compares it to a register defined threshold level ALCSL[3:0] address (0x21). Note: When the ALC automatic
level control is enabled, the function of the ALC is to automatically adjust PGAGAIN[5:0] address (0x2D) volume
setting.
The ALC seeks to control the PGA gain such that the PGA output maintains a constant envelope. This helps to
prevent clipping at the input of the sigma delta ADC while maximizing the full dynamic range of the ADC. The ALC
monitors the output of the ADC, measured after the digital decimator has converted it to 1.23 fixed-point formats. The
ADC output is fed into a peak detector, which updates the measured peak value whenever the absolute value of the
input signal is higher than the current measured peak. The measured peak gradually decays to zero unless a new
peak is detected, allowing for an accurate measurement of the signal envelope. Based on a comparison between the
measured peak value and the target value, the ALC block adjusts the gain control, which is fed back to the PGA.
emPowerAudio
Datasheet Revision 2.0
Coefficient
0x0F
Addr
12.3.3. Digital ADC Gain Control
12.4. PROGRAMMABLE GAIN AMPLIFIER (PGA)
Automatic level control (ALC) or
Input peak limiter
12.4.1. Automatic level control (ALC)
ADCG
Name
™
1
1


tan
tan
Bit 8
A
0








0
2
2
2
2


f
f
s
s
f
f
Table 12: Equations to Calculate Notch Filter Coefficients
b
b
Bit 7








Table 13: Register associated with ADC Gain


1

Bit 6
A
0

x
A
Page 26 of 109
cos
1
Bit5




2

f
s
f
c




Bit 4
(Hz)
ADCGAIN
f
f
fs = sample frequency
c
b
= center frequency (Hz)
= -3dB bandwidth (Hz)
Bit 3
Notation
Bit 2
Bit 1
Register Value (DEC)
(then convert to 2‟s
NAU8812
NFCA0 = -A
NFCA1 = -A
January 2011
complement)
Bit 0
0
1
x 2
x 2
Default
0x0FF
13
12