PCM186X datasheet(32/145 Pages) TI2

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CIC Filter

ADC

Auto

Gain

Control

Analog

PGA

Digital

PGA

Controller

Zero

Cross

Detector

Digital PGA

Overflow Detector

Decimation

Filter

Digital

Mixer

S-Curve

Volume

Mixer

PGA

–12 dB to +32 dB

0.5 dB to 12 dB

–100 dB ~ +18 dB

–100 dB ~ 0 dB

PCM1860, PCM1861, PCM1862

PCM1863, PCM1864, PCM1865

SLAS831D – MARCH 2014 – REVISED MARCH 2018

www.ti.com

Product Folder Links: PCM1860 PCM1861 PCM1862 PCM1863 PCM1864 PCM1865

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9.3.6 Automatic Clipping Suppression

The PCM186x software-controlled devices have the ability to automatically lower the gain in 0.5 dB steps under

the following conditions if the ADC is clipping.

The device detects clipping after the decimation filter in the signal chain, shown in Figure 30, and counts the

number of successive clips before responding.

The device also generates an internal interrupt that can be mapped to a GPIO or interrupt pin, allowing the

system microcontroller to make the decision to increase the gain and consider the clipping an isolated event, or

make the decision that the new gain setting is appropriate.

Figure 30. Sampling Points Within the PCM186x for Auto Clipping Suppression

9.3.6.1 Attenuation Level

This feature is not designed to be a complete analog gain control. This feature was defined to avoid clipping, and

to inform the system microcontroller of a clipping event, to allow the microcontroller (or the end user) to decide if

the gain should be increased again.

The attenuation is programmable to –3 dB, –4 dB, –5 dB, or –6 dB.

9.3.6.2 Channel Linking

Depending on the application, users may not want to link input channels, however, for the majority of stereo input

applications, its strongly recommended to set the system to track gain across inputs, to maintain balance.

The auto PGA clipping suppression control has the settings shown in Table 3.

Table 3. Auto Clipping Suppression Control Registers

LOCATION

USAGE

VALUES

AGC_EN

Pg0 0x05

Enable auto gain control

0: Disable (Default)

1: Enable

CLIP_NUM[1:0]

Pg0 0x05

Start auto gain control after detects CLIP_NUM times of ADC

sample clips

0: 80

1: 40

2: 20

3: 10 (Default)

MAX_ATT[1:0]

Pg0 0x05

Maximum automatic attenuation

0: –3 dB (Default)

1: –4 dB

2: –5 dB

3: –6 dB

DPGA_CLIP_EN

Pg0 0x05

Enable clipping detection after the digital PGA. Note that digital

PGA is post ADC, meaning that there is a short delay before

clipping is detected.

0: Disable (Default)

1: Enable

LINK

Pg0 0x05

Link all channels together if dealing with stereo sources to maintain

balance.

0: Independent control (Default)

1: Ch1[R]/Ch2[L]/Ch2[R] follow Ch1[L] PGA

value.

SMOOTH

Pg0 0x05

Enable smooth transition from step to step (zero crossing).

0: Immediate change

1: Smooth change (default)

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