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SAF7741

Car radio Digital Signal Processor (DSP)

NXP Semiconductors. 

NXP Semiconductors

SAF7741HV

Dual IF car radio and audio DSP (N1F)

IQ FROM IFADC

IQC

LD INTERFACE

AGC

PDC

TO DSP

I2S

TO DIGITAL RADIO COPROCESSOR

TUNER

DSP

I2C

Fig 5. Block diagram of the PDC

The PDC decimates the incoming signal by 16 before shifting it to the baseband and

creating two paths: ‘wanted’ and ‘image’. After another decimation by two, the AGC stage

takes place to compensate for the tuner gain-reduction steps. The linear gain control

stage makes sure that there is maximum use of the dynamic range. After another

decimation by two the IQC stage takes place to compensate for imperfections in the

analog mixer of the tuner by measuring and correcting possible aliases between the

wanted and image signals. The PDC settings allow for different IF bandwidth corrections

and for local oscillator swap of the TEF7000. Communication between the tuner and

SAF7741HV uses the proprietary two-line LD interface for AGC, injection-mode and

bandwidth settings.

The PDC has two data outputs: one parallel inteface to the TDSPs and one I2S-like

interface to the external digital radio co-processor.

7.1.2.1 PDC Input

The PDC input is a complex bit stream from the 5th order converter. The I and Q bit

streams each have a sample rate of 41.6 MSa/s.

7.1.2.2 Input decimation

The input sample rate of 41.6 MSa/s is decimated by 16 MSa/s to 2.6 MSa/s.

7.1.2.3 Shift-to-baseband mixer

For the wanted signal, the TEF7000 tuner has an IF frequency of 300 kHz for FM and

60 kHz for AM: for the image signal these values are −300 kHz and −60 kHz respectively.

The shift-to-baseband mixer shifts the wanted signal by −fmix to baseband and the image

signal by +fmix. The mixer has two independent registers for the wanted frequency

alignment:

• fmix_0 with high-side injection

• fmix_1 with low-side injection

In TEF6730 mode fmix_0 and fmix_1 are 300 kHz for both FM and AM

SAF7741_5

Objective data sheet

Rev. 05 — 09 May 2008

© NXP B.V. 2008. All rights reserved.

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