ADAV803 Analog Devices, ADAV803 Datasheet - Page 17

• Manufacturer Part Number: ADAV803
• Description: Audio Codec
• Manufacturer: Analog Devices

Selecting a Samp
The output sample rate of the ADC is always ADC MCLK/256,
as shown in Figure 23. By default, the ADC modulator runs at
ADC MCLK/2. When the ADC MCLK exceeds 12.288 MHz,
the ADC modulator should be set to run at ADC MCLK/4.
This is achieved by setting the AMC (ADC Modulator Clock)
bit in the ADC Control Register 1. To compensate for the
reduced modulator clock speed, a different set of filters is used
in the decimator section ensuring that the sample rate remains
the same.
The AMC bit can also be used to boost the THD + N perform
ance of the ADC at the expense of dynamic range. The
improvement is typically 0.5 dB to 1.0 dB and works, b
selecting the lower modulator rate reduces the amount of dig
le Rate
NO
INCREASE GAIN BY 0.5dB
FULLY RESTORED?
HAS GAIN BEEN
YES
YES
LIMITED RECOVERY
WAIT FOR SAMPLE
SAMPLES BELOW
HAS RECOVERY
ABOVE ATTACK
THRESHOLD?
THRESHOLD?
REACHED?
RECOVERY
IS SAMPLE
TIME BEEN
YES
NO
ARE ALL
YES
MODE ENABLED?
IS A RECOVERY
AT MAXIMUM?
IS GAINCNTR
INCREMENT
GAINCNTR
NO
NO
NO
YES
ecause
Figure 26. ALC Flow Diagram
Rev. 0 | Page 17 of 56
ital
-
NO
ATTACK MODE
NO
DECREASE GAIN BY 0.5dB
GREATE
AND WAIT ATTACK TIME
WAIT FOR SAMPLE
TH
IS
RESHOLD?
R THAN ATTACK
noise, improving THD + N, but reduces the oversampling r
therefore reducing the dynamic range by a corresponding
amount.
For best performance of the ADC, avoid using similar fre-
quency clocks from separate sources in the ADAV803. For
example, running the ADC from a 12.288 MHz clock connected
to MCLKI and using the PLL to generate a separate 12.288 MHz
clock for the DAC can reduce t
This is due to the interaction o
frequencies that can affect the charge on the switch capacitors
of the analog inputs.
SAMPLE
NO
YES
INCREASE GAIN BY 0.5dB
WAIT RECOVERY TIME
FULLY RESTORED?
WAIT FOR SAMPLE
SAMPLES BELOW
HAS RECOVERY
HAS GAIN BEEN
ABOVE ATTACK
THRESHOLD?
THRESHOLD?
REACHED?
RECOVERY
IS SAMPLE
TIME BEEN
YES
YES
NO
ARE ALL
NORMAL RECOVERY
YES
NO
NO
f the clocks, which generate beat
he performance of the ADC.
ADAV803
atio,