REV. 0–8–
AD74111
FUNCTIONAL DESCRIPTION
General Description
The AD74111 is a 2.5 V mono codec. It comprises an ADC and
DAC channel with single-ended input and output. The ADC
has a programmable gain stage and the DAC has programmable
volume control. Each of these sections is described in further
detail below. The AD74111 is controlled by means of a flexible
serial port (SPORT) that can be programmed to accommodate
many industry standard DSPs and microcontrollers. The AD74111
can be set to operate as a master or slave device. The AD74111
can be set to operate with sample rates of 8 kHz to 48 kHz,
depending on the values of MCLK and the MCLK prescalers.
On-chip digital filtering is provided as part of the DAC and
ADC channels with a low group delay option to reduce the delays
through the filters when operating at lower sample rates. Figure 4
shows a block diagram of the DAC and ADC channel in the
AD74111. Figures 5a and 5b show block diagrams of the filter
arrangements of the ADC and DAC filters.
ADC Section
The AD74111 contains a multibit sigma-delta ADC. The ADC
has a single input pin with additional pins for decoupling/filter
capacitors. The ADC channel has an independent input amplifier
gain stage that can be programmed in steps of 3 dB, from 0 dB
to 12 dB. The input amplifier gain settings are set by program-
ming the appropriate bits in Control Register E. The ADC can
also be muted under software control. The AD74111 input
channel employs a multibit sigma-delta conversion technique that
provides a high resolution output with system filtering imple-
mented on-chip. Sigma-delta converters employ a technique
known as oversampling, where the sampling rate is many times
the highest frequency of interest. In the case of the AD74111,
the oversampling ratio is 64 and a decimation filter is used to
reduce the output to standard sample rates. The maximum sample
rate is 48 kHz.
DAC
DATA
16-/20-/24-
BITS
5 BITS
/4
PRESCALERS
(/1 to /12)
- ADC
MODULATOR
SINC FILTER
(/8)
DECIMATOR
(/8)
MCLK
ADC
DATA
16-/20-/24-
BITS
ADC
INPUT
ADC MODULATOR
CLOCK
DAC O/P
DAC MODULATOR
CLOCK
/2
- DAC
MODULATOR
INTERPOLATOR
( 16)
INTERPOLATOR
( 8)
Figure 4. ADC and DAC Engine
SAMPLE RATE – kHz
54
84 4816
THD+N – dB
24 40
58
62
66
70
74
78
32
TPC 7. ADC THD+N vs. Sample Rate
SAMPLE RATE – kHz
78
84816
THD+N – dB
24 40
80
82
84
86
88
90
32
TPC 8. DAC THD+N vs. Sample Rate
