TDA7514 STMicroelectronics, TDA7514 Datasheet - Page 63

• Manufacturer Part Number: TDA7514
• Description: SINGLE-CHIP FM/AM TUNER
• Manufacturer: STMicroelectronics

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5
5.1 FM TUNER SECTION
5.1.1
The FM tuner section features an image rejection mixer. Its low noise figure allows connecting the antenna
to the mixer without any discrete preamplifier. The external preselection circuit can be realized with one
tuned filter only. The filter can be electrically aligned by shifting the filter tuning voltage with respect to the
VCO tuning voltage through an 8 bit DAC.
The mixer image rejection trimming is obtained by tuning the relative phase offset and relative gain of the
I and Q mixer paths. The mixer output (common with the AM 1st mixer output) is connected to a tuned IF
transformer, with the possibility of electrically adjusting the center frequency through an internal 4 bit ca-
pacitor bank.
The FM AGC can operate in two different software-selectable modes:
The AGC features a single current output used to drive the front end P-I-N diode attenuator.
5.1.2
FM channel selection is mainly done by use of external ceramic filters. Two different software-program-
mable configurations are available:
5.1.3
The TDA7514 features a fully integrated FM demodulator which requires a lower IF than 10.7 MHz. There-
fore a 2nd mixer is provided to down-convert IF1 down to 450 kHz. The 10.25 MHz frequency needed to
drive the 2nd mixer is provided by the XTAL oscillator. Limiting is performed at IF2 through a 5 stage lim-
iter. The demodulator exhibits a very linear frequency-voltage conversion. Precise cancellation of the de-
modulator output voltage offset is available via software control especially for high audio gain WB
applications.
Field strength measurement (Smeter) is performed through use of a separate IF1 limiter and logarithmic
amplifier. The IF1 limiter output is also used to feed the FM IF counter block.
– Keyed Wide band mode: the AGC detects the strength of the wide band RF signal at the input of the
– Wide band + Narrow band mode: the AGC detects the strength of both the wide band RF signal at
– normal FM mode: three ceramic filters can be connected using two impedance-matched IF amplifiers
– high-performance Weather Band applications: when an optimum Weather Band channel selection is
FUNCTIONAL DESCRIPTION
1st mixer to activate the AGC attenuation; the starting point is programmable via software and is var-
ied over a >40 dB range by the very narrow band Smeter signal in order to set a maximum suppres-
sion limit that prevents the desired channel from decreasing below an acceptable level;
the input of the 1st mixer and of the narrow band IF signal at the output of the IFT1(both starting points
are software-programmable); this mode allows a smooth transition between near adjacent and far ad-
jacent suppression.
(both with programmable gains); the third ceramic filter is connected to the 2nd mixer input;
required, the TDA7514 allows to connect a dedicated narrow band external 450 kHz ceramic filter to
implement this function. In this case only two 10.7 MHz ceramic filters can be connected for standard
FM selectivity. The 1st ceramic filter is normally connected between the IFT1 output and the 1st IF
amplifier input; the 2nd ceramic filter is connected between the 1st IF amplifier input and the 2nd mix-
er input; the 450 kHz WB filter is connected between the 2nd IF amplifier output and the 2nd IF am-
plifier input. Both the single standard FM IF amplifier gain and the 450 kHz WB filter driver IF amplifier
gain are software programmable.
FRONT END
IF FILTERING
LIMITING AND DEMODULATION
TDA7514
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