Atmel ATR4262M1 Portable Radio User Manual


 
5
4994BS–AUDR–05/08
ATR4262M1 [Preliminary]
6. Functional Description
The ATR4262M1 front end is designed for world-tuner applications. Due to its flexible divider
arrangement, the tuner can be used for reception from 100 kHz to 163 MHz. The field of use
covers all the common radio broadcast services from AM-LW to AM-SW (up to 30 MHz) and
from FM-OIRT to US weatherband. The tuner application can be easily adapted to the require-
ments of DRM and HD-radio (IBOC).
FM section
The ATR4262M1 contains a high performance FM image rejection mixer, which helps to
reduce the demands and the cost of the front end application. The FM mixer output can be
switched to an alternative pair of pins to allow different IF filter concepts for FM mode. Two
selectable inputs can be used for independent FM front end sections.
AM section
The AM section contains a dedicated AM prescaler for the LO signal. Very small tuning
steps are possible using this divider, while at the same time a high PLL comparison fre-
quency guarantees excellent phasenoise behavior.
•RF-AGC
Both AM and FM signal paths have their own RFAGCs with a wideband and a inband detec-
tor with individual thresholds. The thresholds for AM and FM can be programmed in 2 dB
steps. An optional keyed AGC function reduces the wideband AGC threshold up to 6 dB in
order to avoid desensitization of the tuner. Pin diode drivers for AM and FM are integrated to
reduce cost for external components. In addition to the pin diode control, a cascode control
voltage for the external LNA is provided by the AM-AGC block.
•IF stage
The IF amplifier has three selectable inputs, which can be matched to any common IF filter
impedance by external components. With these inputs, the tuner application can be easily
adapted to different broadcast standards, while conventional standards are still possible.
Gain can be set via pins or by setting bits, which makes the ATR4262M1 very versatile and
easy to adapt to different baseband architectures.
Fractional PLL
The ATR4262M1 contains a complete fractional PLL, which guarantees fast lock time, low
phase noise and small tuning steps. A reference clock frequency from 9 kHz up to 21 MHz
provided by, for example, baseband can be used. Alternatively the integrated XCO with
standard crystals from 10 MHz to 21 MHz can be used as the reference for the PLL.
Double tuner concept
Like phase diversity or background tuning, double-tuner applications are also possible. For
phase diversity applications, the tuner can also operate in slave mode with a master tuner
providing the VCO frequency for both tuners.
Digital electronic alignment
Two independent gain and offset programmable DACs are available to tune the FM front
end section. The PLL’s tuning voltage is used as input for the DACs to ensure proper track-
ing to the reception frequency. In slave mode, the tuning voltage of a master tuner must be
applied to a dedicated input pin.