SAF784X datasheet(61/93 Pages) NXP

61 / 93 page

SAF784X_2

Product data sheet

Rev. 02 — 9 May 2008

61 of 93

NXP Semiconductors

SAF784x

One chip CD audio device with integrated MP3/WMA decoder

• Sigma-delta noise shaper: this block regenerates a PDM data stream from a given

multi-bit value, which is provided at its inputs.

6.7.1 Modes of operation

The ﬂexible servo can be used in six main modes, they are described in the following

sections.

6.7.1.1

Hardware servo-only

This mode uses the hardware servo (PDSIC) only without any additional processing

taking place on either the diode input signals or the servo output signals.

6.7.1.2

Hardware servo with ﬁne offset compensation

This mode is the same as hardware servo-only mode but has the addition of the ﬁne offset

compensation functionality in the digital domain. The ﬁne offset compensation is

additional to the coarse offset compensation, which is available in all ﬂexible servo modes.

6.7.1.3

Fully ﬂexible servo

Also known as software servo. The diode signals have the ﬁne offset applied to them and

are passed to registers for reading by the ARM microprocessor. The complete servo

functionality is implemented in software running on the ARM; the PDSIC hardware servo

is switched out of the loop entirely. The ARM calculates values, which are used to

generate servo signals for driving the mechanism actuators. The PDM generation for the

servo output signals is performed by the sigma-delta block.

6.7.1.4

Pre-processing with hardware servo

The diode signals have the ﬁne offset applied to them and are passed to registers for

reading by the ARM microprocessor. The ARM pre-processes these signals and they are

fed back to the inputs of the hardware servo via sigma-delta noise shapers. The hardware

servo (PDSIC) performs all the control functions (on the modiﬁed input signals) and

outputs the servo signals as hardware servo-only mode.

6.7.1.5

Hardware servo with post-processing

The diode signals are passed directly to the hardware servo inputs (can be with, or

without, ﬁne-offset compensation added). The PDSIC servo output signals are passed to

registers for reading by the ARM microprocessor. The ARM executes any post-processing

it deems necessary on the signals and passes new values back which are used to drive

the mechanism actuators. The servo outputs are therefore generated by the ARM, rather

than the PDSIC, but based on the signals provided by the PDSIC.

6.7.1.6

Pre-processing with hardware servo plus post-processing

The diode signals have the ﬁne offset applied to them and are passed to registers for

reading by the ARM microprocessor. The ARM pre-processes these signals and they are

fed back to the inputs of the hardware servo via sigma-delta noise shapers. The hardware

servo performs all the control, and the servo output signals are passed to registers for

reading by the ARM microprocessor. The ARM executes any post-processing it deems

necessary on the signals and passes new values back which are used to drive the

mechanism.

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