Datasheet

TEF6901A_3 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 03 — 20 March 2008 9 of 107
NXP Semiconductors
TEF6901A
Integrated car radio
7.12 Antenna DAA
For FM operation the antenna Digital Auto Alignment (DAA) measures the VCO tuning
voltage and multiplies it with a factor defined by the 7-bit DAA setting to generate a tuning
voltage for the FM antenna tank circuit (RF selectivity). In AM mode the DAA setting
controls a fixed voltage.
7.13 AM RF AGC control
The AM front-end is designed for the application of an external Junction Field Effect
Transistor (JFET) low noise amplifier with cascode AGC and PIN diode AGC both
controlled by an integrated AGC control circuit. Four AGC thresholds of the detector at the
first mixer input are selectable via I
2
C-bus. Detectors at the RF mixer input and at the
AMIF2 input prevent undesired overload (see Figure 40). AGC information can be read
out via I
2
C-bus. The PIN diode current drive circuit includes a pull-up current source for
reverse biasing of the PIN diode, when the AGC is not active to achieve a low parasitic
capacitance.
7.14 AM mixer 1
The large dynamic range AM mixer converts AM RF (144 kHz to 26.1 MHz) to an IF
frequency of 10.7 MHz.
7.15 AM IF noise blanker
The spike detection for the AM IF noise blanker is at the output of the AM front-end mixer.
Blanking is realized at the second AM mixer.
7.16 AM IF AGC amplifier and demodulator
The 450 kHz IF2 signal after the ceramic channel selection filter is amplified by the
IF AGC amplifier and demodulated.
7.17 AM level detection
The IF2 signal used for AM IF AGC and demodulation is also used in the limiter circuit for
in-band level detection.
7.18 AM and FM level DAA
The start and slope of the level detector output are programmable to achieve level
information independent of gain spread in the signal channel.
7.19 AM and FM IF counter
The output signal from the limiter is used for IF counting in both AM and FM.
7.20 Tuning mute
A soft slope tuning mute is controlled by the sequential machine for different tuning
actions to eliminate audible effects of tuning and band switching.