FM ραδιόφωνο σε ένα chip

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mixos

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FM ραδιόφωνο σε ένα chip

« on: July 26, 2003, 22:24:11 pm »

Το ολοκληρωμένο ΑΝ192 αποτελεί μαζί με κάποια ελάχιστα εξωτερικά εξαρτήματα ενα πλήρες ραδιόφωνικό δέκτη στα FM.
Περιγραφή από application note της philips:

Until now, the almost total integration of an FM radio has been
prevented by the need for LC tuned circuits in the RF, IF, local
oscillator and demodulator stages. An obvious way to eliminate the
coils in the IF and demodulator stages is to reduce the normally
used intermediate frequency of 10.7MHz to a frequency that can be
tuned by active RC filters, the op amps and resistors of which can
be integrated. An IF of zero deems to be ideal because it eliminates
spurious signals such as repeat spots and image response, but it
would not allow the IF signal to be limited prior to demodulation,
resulting in poor signal-to-noise ratio and no AM suppression. With
an IF of 70kHz, these problems are overcome and the image
frequency occurs about halfway between the desired signal and the
center of the adjacent channel. However, the IF image signal must
be suppressed and, in common with conventional FM radios, there
is also a need to suppress interstation noise and noise when tuned
to a weak signal. Spurious responses above and below the center
frequency of the desired station (side tunings), and harmonic
distortion in the event of very inaccurate tuning must also be
eliminated.
We have now developed a mono FM reception system which is
suitable for almost total integration. It uses an active 70kHz IF filter
and a unique correlation muting circuit for suppressing spurious
signals such as side responses caused by the flanks of the
demodulator S-curve. With such a low IF, distortion would occur with
the ±75kHz IF swing due to received signals with maximum
modulation. The maximum IF swing is therefore compressed to
±15kHz by controlling the local oscillator in a frequency-locked loop
(FLL). The combined action of the muting circuit and the FLL also
suppresses image response.
The new circuit is the TDA7000 which integrates a mono FM radio
all the way from the aerial input to the audio output. External to the
IC are only one tunable LC circuit for the local oscillator, a few
inexpensive ceramic plate capacitors and one resistor. The
TDA7000 dramatically reduces assembly and post-production
alignment costs because only the oscillator circuit needs adjustment
during manufacture to set the limits of the tuned frequency band.
The complete FM radio can be made small enough to fit inside a
calculator, cigarette lighter, key-ring fob or even a slim watch. The
TDA7000 can also be used as receiver in equipment such as
cordless telephones, CB radios, radio-controlled models, paging
systems, the sound channel of a TV set or other FM demodulating
systems.
Using the TDA7000 results in significant improvements for all
classes of FM radio. For simpler portables, the small size, lack of IF
coils, easy assembly and low power consumption are not the only
attractive features. The unique correlation muting system and the
FLL make it very easy to tune, even when using a tiny tuning knob.
For higher-performance portables and clock radios,
variable-capacitance diode tuning and station presetting facilities are
often required. These are easily provided with the TDA7000
because there are no variable tuned circuits in the RF signal path.
Only the local oscillator needs to be tuned, so tracking and distortion
problems are eliminated.
The TDA7000 is available in either an 18-lead plastic DIP package
(TDA7000), or in a 16-pin SO package (TDA7010T). Future
developments will include reducing the present supply voltage (4.5V
typ.), and the introduction of FM stereo and AM/FM versions.
SR01154


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