Datasheet

ManualsBrandsMAXIM INTEGRATED ManualsLinear ICsMAX9860ETG+

MAX9860

16-Bit Mono Audio Voice Codec

Maxim Integrated

Automatic Gain Control (AGC)

and Noise Gate

The MAX9860 includes AGC on both microphone

inputs. AGC is enabled by setting the hold time through

AGCHLD. AGC dynamically controls the analog PGA

microphone input gain to hold the level constant over a

20dB input range, enhancing the voice path operation

for various use conditions. When AGC is enabled, it

monitors the signal level at the output of the ADC and

then makes gain adjustments by controlling the analog

microphone PGA. When AGC is enabled, PGAM is not

user programmable.

Since AGC increases the level of all signals below a

user-defined threshold, the noise floor effectively is

increased by 20dB. To counteract this, a noise gate is

included to reduce the gain at low levels. Unlike typical

noise gates that completely silence the output below a

threshold, the noise gate in the MAX9860 reduces the

gain for signals below the defined level. As the signal

level becomes further below the threshold, the gain is

further reduced. The Automatic Gain Control

Thresholds and Noise Gate Thresholds graphs in the

Typical Operating Characteristics

show the resulting

steady-state transfer curves when AGC and the noise

gate are enabled.

Table 10. AGC and Noise Gate Registers

0x0E AGCSRC AGCRLS AGCATK AGCHLD

0x0F ANTH AGCTH

BITS FUNCTION

AGCSRC

AGC/Noise Gate Signal Source Select

0 = The left ADC output is used by the AGC and noise gate.

1 = The sum of the left and right ADC outputs is used by the AGC and noise gate.

AGC Release Time

Time taken by the AGC circuit to increase the gain from minimum to maximum.

CODE TIME

000 78ms

001 156ms

010 312ms

011 625ms

100 1.25s

101 2.5s

110 5s

AGCRLS

111 10s

AGC Attack Time

The time constant of the AGC gain reduction curve.

CODE TIME (ms)

00 3

01 12

10 50

AGCATK

11 200

AGC Hold Time

Time the AGC circuit waits before beginning to increase gain when a signal below the threshold is

detected.

CODE TIME (ms)

00 AGC disabled

01 50

10 100

AGCHLD

11 400