SAF7741 Просмотр технического описания (PDF) - NXP Semiconductors.

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SAF7741

Car radio Digital Signal Processor (DSP)

NXP Semiconductors. 

NXP Semiconductors

SAF7741HV

Dual IF car radio and audio DSP (N1F)

When there is a gain change of more than 12 dB this is made step-wise without running

the compensation waveform. This is the case with either Alternate Frequency (AF)

updates or a pre-set change. These functions are always used in a muted condition and

are therefore not audible.

7.1.2.8 Step-response timing

In order to align for the bandwidth of the analog circuits, an alignment is made between

the response length and the response delay. This alignment is separate for the wideband

and the IF responses.

Both the delay and the response length for the IF response are dominated by the PDC

response before the AGC. These values are independent of the tuner response. The

wideband response is different for analog and for digital AM/FM.

DELAY

RESPONSE LENGTH

DELAY

RESPONSE LENGTH

a: Low Bandwidth Step response

b: High Bandwidth Step response

Fig 8. Step response length alignment for different tuner bandwidths

7.1.2.9 Perfect step compensation

Perfect step compensation of the tuner gain steps is made possible for signals within the

IF signal band by alignments of amplitude, waveform and waveform delay. Near-perfect

alignment is possible for off-centre signals within the IF signal band.

7.1.2.10 Non-perfect step compensation

Perfect compensation of the tuner gain steps is not possible for signals outside the IF

signal band. In such cases the resulting interference must be suppressed. In the PDC,

four signalling bits are provided for this purpose:

• AGC_A_CHANGE

• AGC_B_CHANGE

• AGC_C_CHANGE

• AGC_D_CHANGE

These bits can be read by the DSP and a soft-mute signal can be generated when

required.

7.1.2.11 AGC linear gain

Data-path signals that exceed a certain level are kept constant in a linear controlled-gain

stage (see Figure 9). Linear control avoids overload of the following signal stages and

makes sure that maximum use is made of the data path’s dynamic range. The I2C

interface sets the reference level for linear control as well as the corresponding attack and

delay values.

SAF7741_5

Objective data sheet

Rev. 05 — 09 May 2008

© NXP B.V. 2008. All rights reserved.

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