Texas Instruments LM49370RLEVAL Evaluation Board LM49370RLEVAL/NOPB LM49370RLEVAL/NOPB 데이터 시트
제품 코드
LM49370RLEVAL/NOPB
SNAS356D – FEBRUARY 2007 – REVISED MARCH 2012
Table 13. ADC_2 (0x07h) (continued)
Bit
Field
Description
s
4:2
AGC_FRAME_TIME
This sets the frame time to be used by the AGC algorithm. In a given frame, the AGC's peak detector
determines the peak value of the incoming microphone audio signal and compares this value to the target
value of the AGC defined by AGC_TARGET (bits [3:1] of register (0x08h)) in order to adjust the microphone
preamplifier's gain accordingly. AGC_FRAME_TIME basically sets the sample rate of the AGC to adjust for a
wide variety of speech patterns.
determines the peak value of the incoming microphone audio signal and compares this value to the target
value of the AGC defined by AGC_TARGET (bits [3:1] of register (0x08h)) in order to adjust the microphone
preamplifier's gain accordingly. AGC_FRAME_TIME basically sets the sample rate of the AGC to adjust for a
wide variety of speech patterns.
(1)
AGC_FRAME_TIME
Time (ms)
000
2
96
001
2
128
010
2
192
011
2
256
100
2
384
101
2
512
110
2
768
111
2
1000
6:5
ADC_CLK
This selects the clock to be used by the audio ADC system.
ADC_CLK
Source
00
2
MCLK
01
2
PLL_OUTPUT
10
2
I2S_CLK_IN
11
2
PCM_CLK_IN
7
NGZXDD
If set, the noise gate will not wait for a zero crossing before mute/unmuting. This bit should be set if the ADC's
HPF is disabled and if there is a large DC or low frequency component at the ADC input.
HPF is disabled and if there is a large DC or low frequency component at the ADC input.
NGZXDD
Result
0
Noise Gate operates on ZXD events
1
Noise Gate operates on frame boundaries
(1)
Refer to the
for further detail.
AGC_1 CONFIGURATION REGISTER
This register is used to control the LM49370's Automatic Gain Control.
(2)
Table 14. AGC_1 (0x08h)
Bit
Field
Description
s
If set, the AGC controls the analog microphone preamplifier gain into the system. This feature is useful for
0
AGC_ENABLE
microphone signals that are routed to the ADC.
3:1
AGC_TARGET
This programs the target level of the AGC. This will depend on the expected transients and desired headroom.
Refer to AGC_TIGHT (bit 7 of 0x09h) for more detail.
Refer to AGC_TIGHT (bit 7 of 0x09h) for more detail.
AGC_TARGET
Target Level
000
2
−
6 dB
001
2
−
8 dB
010
2
−
10 dB
011
2
−
12 dB
100
2
−
14 dB
101
2
−
16 dB
110
2
−
18 dB
111
2
−
20 dB
If set, signals below the noise gate threshold are muted. The noise gate is only activated after a set period of
4
NOISE_GATE_ON
signal absence.
(2)
See the
24
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