STA538B datasheet(23/59 Pages) STMICROELECTRONICS

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STA538

ADC

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ADC

This section describes the analog-to-digital converter (ADC).

6.1

Functional description

The STA538 analog input is provided through a low power, low voltage, stereo audio analog-

to-digital converter front-end designed for audio applications. It includes a programmable

gain amplifier, anti-aliasing filter, low-noise microphone biasing circuit, a third-order

MASH2-1 delta-sigma modulator, digital decimating filter, and a first-order DC-removal filter.

This device is fabricated using a 0.18 µm CMOS process, where high-speed precision

analog circuits are combined with high-density logic circuits.

The ADC works in a microphone input (mic-in) mode and in a line-input mode.

If the line input mode is selected, the ADC is configured in stereo and all conversion

channels are active.

If the microphone input mode is selected, the ADC is configured in mono. The mono

channel is routed through the left conversion path, and the right conversion path is kept in

power-down mode to minimize power consumption. A programmable gain amplifier (PGA) is

available in mic-in mode, giving the possibility to amplify the signal from 0 to +42 dB in steps

of 6 dB.

6.1.1

Digital filter characteristics

The digital filter characteristics are shown in Table 15.

Table 15.

Digital filter characteristics

Parameter

Typical

Unit

Passband

0.4535 * Fs

kHz

Passband ripple:

Fs mode

Fs_by_2 mode

Fs_by_4 mode

0.08 at 44.1 kHz

0.08 at 22.05 kHz

0.08 at 11.025 kHz

Stop band attenuation:

Fs mode

Fs_by_2 mode

Fs_by_4 mode

45 at 44.1 kHz

45 at 22.05 kHz

45 at 11.025 kHz

Group delay:

Fs mode

Fs_by_2 mode

Fs_by_4 mode

0.4 at 32 kHz

0.7 at 16 kHz

1.4 at 8 kHz

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