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2003 Oct 21
11
Philips Semiconductors
Product specification
Car radio tuner front-end for digital IF
TEF6700HL
7.10
AM tuner including mixer 1 and mixer 2
The AM tuner is realized in a double conversion technique
and is capable of selecting LW, MW and SW bands.
AM mixer 1 converts AM RF to an IF1 of 10.7 MHz, while
AM mixer 2 converts IF1 of 10.7 MHz to IF2 of 450 kHz:
LW from 144 to 288 kHz
MW from 522 to 1710 kHz (US AM band)
SW from 5.73 to 9.99 MHz (including the 31 m, 41 m
and 49 m bands).
7.11
AM RFAGC
The AM wideband AGC in front of the AM mixer 1 is
realized first by a cascoded NPN transistor, which controls
the transconductance of the RF amplifier JFET with 10 dB
of AGC range. Second, an AM PIN diode stage with 30 dB
of AGC range is available. The minimum JFET drain
source voltage is controlled by a DC feedback loop (pin
VAMCASFB) in order to limit the cascode AGC range to
10 dB. If the cascode AGC is not required, a simple
RF AGC loop is possible by using only a PIN diode.
In some conditions, noise behaviour will increase. In this
case pins VAMCAS and VAMCASFB have to be left
open-circuit. In FM mode, the cascode switches off the
JFET bias current to reduce total power consumption. The
PIN diode is biased by 1 mA in FM mode.
The AGC detection points for AM RF AGC are at the AM
mixer 1 input (threshold programmable via the I
2
C-bus)
and the IF2 AGC input (fixed threshold).
7.12
AM noise blanker
The detection point for the AM noise blanker is the output
stage of AM mixer 1, while blanking is realized at the
output of mixer 2.
7.13
AM IF2 AGC
This is a linear AM IF2 AGC amplifier. The gain controlled
AM IF2 is output via the multiplexed FM IF/AM IF2 buffer
to a car IF DSP IC (e.g. SAA7724H).
7.14
FM IF and AM IF2 buffer
This buffers and multiplexes AM IF2 and FM IF to pin
IFOUT.
7.15
FM and AM level detector
The FM and AM level detectors provide the temperature
compensated output voltage. The starting points and
slopes of the level detector outputs are programmable via
the I
2
C-bus.
7.16
FM/AM RFAGC buffer
The output (open-collector) sinks a current which in
AM mode is proportional to the voltage at pin TRFAMAGC
and in FM mode proportional to the RF level detector
voltage (pin TFMAGC) inside the FM AGC.