User's Manual

Figure 14: ADC analogue amplifier block diagram

The second stage of the analogue amplifier shown in Figure 14 has a programmable gain with seven

individual 3dB steps. In simple terms, by combining the 24dB gain selection of the microphone input

with the seven individual 3dB gain steps, the overall range of the analogue amplifier is approximately -

3dB to 42dB in 3dB steps. The overall gain control of the ADC is controlled by a VM function. See

iWRAP user guide how to set the gain using iWRAP commands.

7.2.2 DAC

The DAC consists of two third-order Sigma Delta converters allowing two separate channels that are

identical in functionality as shown in Figure 14.

Each DAC supports the following samples rates:

 8kHz

 11.025kHz

 16kHz

 22.050kHz

 24kHz

 32kHz

 44.1kHz

 48kHz

See the iWRAP user guide how to set the sampling rate using iWRAP commands. The default setting

for A2DP is 44.1 kHz and for HFP 8 kHz.

The DAC contains two gain stages for each channel: a digital and an analogue gain stage. The digital

gain stage has a programmable selection value in the range of 0 to 15 with associated DAC gain

settings. This is summarised in Table 14. 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 Selection Value

ADC Digital Gain Setting (dB)

3.5

9.5

15.5

21.5

-24

-20.5