User's Manual

37
7.2.1 ADC
The ADC consists of two second-order Sigma Delta converters allowing two separate channels that are
identical in functionality, as shown in Figure 13Figure 14.
Each ADC supports the following sample rates:
 8kHz
 11.025kHz
 16kHz
 22.05kHz
 24kHz
 32kHz
 44.1kHz
The ADC contains two gain stages for each channel, an analogue and a digital gain stage. The digital
gain stage has a programmable selection value in the range of 0 to 15 with the associated ADC gain
settings summarised in Table 13. There is also a high resolution digital gain mode that allows the gain
to be changed in 1/32dB steps. Please contact Bluegiga Technologies for more information.
Gain SelectionValue
ADC Digital Gain Setting (dB)
0
0
1
3.5
2
6
3
9.5
4
12
5
15.5
6
18
7
21.5
8
-24
9
-20.5
10
-18
11
-14.5
12
-12
13
-8.5
14
-6
15
-2.5
Table 13: ADC digital gain rate selection
The ADC analogue amplifier is a two-stage amplifier. The first stage of the analogue amplifier is
responsible for selecting the correct gain for either microphone input or line input and, therefore, has
two gain settings, one for the microphone and one for the line input. See section 6.2.5 and section 6.2.6
for details on the microphone and line inputs, respectively. In simple terms, the first stage amplifier has
a selectable 24dB gain stage for the microphone and this creates the dual programmable gain required
for the microphone or the line input. The equivalent block diagram for the two stages is shown in Figure
14.