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MC13027 Просмотр технического описания (PDF) - Motorola => Freescale

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MC13027
Motorola
Motorola => Freescale Motorola
MC13027 Datasheet PDF : 28 Pages
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MC13027 MC13122
AMAX STEREO CHIPSET
What is AMAX?
In 1993, a joint proposal by the EIA (Electronic Industries
Association) and the NAB (National Association of
Broadcasters) was issued. It included a unified standard for
pre–emphasis and distortion for broadcasters as well as a set
of criteria for the certification of receivers. The purpose of this
proposal was to restore quality and uniformity to the AM band
and to make it possible for the consumer to receive high
quality signals using the AM band. The FCC has been
supportive of this initiative and has required all new
broadcast licensees to meet AMAX standards. The NAB and
EIA have continued to encourage receiver manufacturers by
offering the AMAX certification logo to be displayed on all
qualifying radios. This logo is shown below.
or
The Receiver Criteria
An AMAX receiver must have wide bandwidth: 7.5kHz for
home and auto, 6.5 kHz for portables. It must have some
form of bandwidth control, either manual or automatic,
including at least two bandwidth provisions, such as “narrow”
and “wide”. It must meet NRSC receiver standards for
distortion and deemphasis. It must have provisions for an
external antenna. It must be capable of tuning the expanded
AM band (up to 1700 kHz). And finally, home and auto
receivers must have effective noise blanking. All of these
requirements, except the noise blanking, have been met by
Motorola’s previous AM radio products, such as MC13025
Front End and the MC13022A C–QUAM stereo decoder. It is
the Noise Blanker requirement which is met by the two
devices on this data sheet, the MC13027 and MC13122.
Noise blanking, especially in AM auto radios, has become
extremely important. The combination of higher energy
ignitions, using multiple spark coils, along with increased use
of plastic in the auto body, have increased the noise energy
at the radio. Also, the consumer has learned to expect higher
quality audio due to advances in many other media. For the
AM band to sustain interest to the consumer, a truly effective
noise blanker is required.
The block diagram below shows the Motorola AMAX
stereo chipset. It offers a two–pronged approach to noise
blanking which is believed to be the most effective yet offered
in the consumer market. The initial blanking takes place in
the output of the mixer, using a shunt circuit triggered by a
carefully defined wideband receiver. For most noises, some
residual audible disturbance is almost always still present
after this process. The disturbance becomes stretched and
delayed as it passes through the rest of the selectivity in the
receiver. The stretching and delay are predictable, so the
MC13027 can provide a noise blanking pulse with the correct
delay and stretch to the output stages of the MC13122
decoder. The MC13122 has a Track and Hold circuit which
receives the blanking signal from the Front End and uses it to
gently hold the audio wherever it is as the pulse arrives, and
hold that value until the noise has passed. The combined
effect is dramatic. A wide range of types of noise is
successfully suppressed and the resulting audio seems
almost clean until the noise is so intense that the blanking
approaches full–time.
The amount of extra circuitry to accomplish noise blanking
is relatively small. The external components for this added
capability are shown in Figure 3. In the MC13027 Front end,
the noise receiver/detector requires two capacitors. The
presettings for blanking timing and blanking delay require
three external fixed resistors. Finally the decoder requires
two track and hold capacitors to store the “audio” voltage
during the track and hold function.
Figure 3. AMAX Stereo Receiver with Noise Blanker
RF In
RF
Amplifier
Pin
Diode
Wideband
AGC
4.0 V
Regulator
MC13027
Mixer
IF
Amplifier
AGC’d IF
Amplifier
AM
Stereo
Decoder
MC13122
Track
and
Hold
Left
Variable
Notch Filter
Right
Divide
by 4
VCO
450 kHz
Filter
AGC’d RF
Amplifier
AM
Detector
AGC
RF Attenuate
RF
Attenuator
Switch
RF Blank
Timer
Audio
Reject
Filter
Pulse
Detector
Audio Blank
Reset
Delay
Timer
Audio Blank
Timer
Audio
Blank
Switch
6
MOTOROLA ANALOG IC DEVICE DATA

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