BC352239A Datasheet, PDF (74/116 Pages) List of Unclassifed Manufacturers – BlueCore 3-Multimedia External

Device Terminal Descriptions
Gain Selection Value
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
ADC Digital Gain Setting (dB)
0
3.5
6
9.5
12
15.5
18
21.5
-24
-20.5
-18
-14.5
-12
-8.5
-6
-2.5
Table 8.20: 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 8.8.24 and Section 8.8.25 for details on the microphone and
line inputs respectively. In simple terms the first stage amplifier has a selectable 20dB 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 stage is shown in Figure 8.10.
2
Differential
20dB Gain
Selection.
Note: Input
Impedance
Function of Mode
Selection
Microphone
Line
Ref
(0.66V)
3dB x 7 Steps
2
A
Differential
2
Differential
First Stage
Second Stage
Figure 8.10: First Stage of ADC Analogue Amplifier Block Diagram
The second stage of the analogue amplifier shown in Figure 8.10 has a programmable gain with seven individual
3dB steps. In simple terms, by combining the 20dB gain selection of the microphone input with the seven
individual 3dB gain steps, the overall range of the analogue amplifier is approximately -4dB to 40dB. The overall
gain control of the ADC is controlled by the a VM function and this setting is a combined function of the digital
and analogue amplifier settings, so that the fullscale range of the input to the ADC is kept to approximately
400mV rms
BC352239A-ds-001Pc
© Cambridge Silicon Radio Limited 2004
Production Information
Page 74 of 116