WM9713 datasheet(32/111 Pages) WOLFSON

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WM9713L

Preliminary Technical Data

PTD, March 2004, Rev 2.2

ATTACK (GAIN RAMP-DOWN) TIME

Attack time is the time that it takes for the PGA gain to ramp down across 90% of its range (e.g. from

27.75dB down to –15B gain). The time it takes for the recording level to return to its target value

therefore depends on both the attack time and on the gain adjustment required. If the gain

adjustment is small, it will be shorter than the attack time. The attack time can be programmed in

power-of-two (2

n) steps, from 6ms, 12ms, 24ms, etc. to 6.14s.

When operating in stereo, the peak detector takes the maximum of left and right channel peak

values, and any new gain setting is applied to both left and right PGAs, so that the stereo image is

preserved. However, the ALC function can also be enabled on one channel only. In this case, only

one PGA is controlled by the ALC mechanism, while the other channel runs independently with its

PGA gain set through the control register.

When one ADC channel is unused, the peak detector disregards that channel. The ALC function can

also operate when the two ADC outputs are mixed to mono in the digital domain, but not if they are

mixed to mono in the analogue domain, before entering the ADCs.

ALC ZERO CROSS

The ALC has a zero cross detection circuit. When enabled, the PGA gain will be updated when the

signal is at zero or after a time out period. This is controlled through the ALC enable ALCZC, register

62h bit 8, and the time out control ZCTIMEOUT, register 62h bit 10:9. The time out signal is a

function of the BITCLK period as defined in Table 13.

WM9713 数据表(PDF) 32 Page - Wolfson Microelectronics plc