lm4935rlx National Semiconductor Corporation, lm4935rlx Datasheet - Page 35

• Manufacturer Part Number: lm4935rlx
• Description: Audio Sub-system With Dual-mode Stereo Headphone And Mono High Efficiency Loudspeaker Amplifiers And Multi-purpose Adc
• Manufacturer: National Semiconductor Corporation

Bits
12.0 Status & Control Registers
12.13 AGC_2 CONFIGURATION REGISTER
This register is used to control the LM4935’s Automatic Gain Control.
3:0
6:4
Note 17: The AGC can be used to control the analog path of the microphone to the output stages or to optimize the microphone path for recording on the ADC.
When the analog path is used this bit should be set to ensure the target is tightly adhered to. If the ADC is the only destination of the microphone or the desired analog
mixer level is line level then AGC_TIGHT should be cleared, allowing greater dynamic rage of the recorded signal. For further details see the AGC overview.
7
AGC_MAX_GAIN
AGC_TIGHT = 0
AGC_TIGHT = 1
AGC_DECAY
AGC_TIGHT
Field
This programs the maximum gain that the AGC algorithm can apply to the microphone preamplifier.
Programs the speed at which the AGC will increase gains if it detects the input level is a quiet
signal.
If set the AGC algorithm controls the microphone preamplifier more exactly. (Note 17)
AGC_MAX_GAIN
0100
AGC_TARGET
AGC_DECAY
0000
0001
0010
0011
1101
1110
1111
2
000
001
010
100
101
000
001
010
100
101
000
001
010
100
101
011
110
111
011
110
111
011
110
111
to 1100
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
TABLE 14. AGC_2 (0x09h)
2
(Continued)
35
Description
Min Level
−10 dB
−12 dB
−14 dB
−16 dB
−18 dB
−20 dB
−10 dB
−12 dB
−14 dB
−16 dB
−18 dB
−20 dB
−6 dB
−8 dB
−6 dB
−8 dB
Max Preamplifier Gain
14 dB to 30 dB
Step Time (ms)
10 dB
12 dB
32 dB
34 dB
36 dB
6 dB
8 dB
1024
2048
4096
128
256
512
32
64
Max Level
−10 dB
−13 dB
−15 dB
−17 dB
−11 dB
−3 dB
−4 dB
−5 dB
−6 dB
−7 dB
−8 dB
−9 dB
−3 dB
−5 dB
−7 dB
−9 dB
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