DIGITAL RADIO SIGNAL PROCESSING
Excerpt from a Blaupunkt News Release
FOR AM & FM
Blaupunkt DigiCeiver® AM/FM tuner technology converts radio frequency signals into digital data.
Blaupunkt has developed a revolutionary digital radio signal processing technology that will obsolete most
of the circuitry in conventional AM/FM radios. By converting radio signals into digital data, Blaupunkt DigiCeiver technology offers major improvements in reception capability, sound quality,
and convenience compared to conventional radios. DigiCeiver technology will first be used in a new line of Blaupunkt car stereos being introduced later this year.
Although so called "digital radios" have been sold for years, these merely have digital station displays and use digital IC's to generate analog reference signals. They do not
process the signal in the digital domain, and the signal path is pure analog from antenna to speaker.
DigiCeiver technology operates in a manner analogous to digital audio, but at much higher frequencies. Just as analog sound waves are converted into the bits and bytes of digital audio data,
DigiCeiver converts analog radio frequency signals into digital data. Once this is done, digital software is used to produce high quality stereo sound, reduce interference and distortion, extract RDS (Radio Data System) and other data subcarriers, and to provide a high level of digital control over the functioning of the analog front end circuitry. In addition to improving
radio reception, DigiCeiver technology will provide a digital pathway with direct digital inputs for better audio integration with CD players, RDS, computers,navigation and other automotive
DigiCeiver technology is made possible by the development of high speed A/D (analog to digital) converters operating at 14.25 MHz, roughly 325 times faster than the A/D converters used for digital
audio. This A/D converter digitizes the modulated 10.7 MHz IF(intermediate frequency) carrier from the RF front end circuitry. Once this is done, all further filtering, demodulation, and multiplex
processing are performed as mathematical calculations in the digital domain. The only analog circuits are the antenna input RF amplifier,mixer and the first IF filter.
With two integrated circuit chips and digital signal processing software, DigiCeiver eliminates a whole range of conventional radio circuits -- IF filters, IF amplifiers, stereo detectors,
demodulators, multiplex filters, RDS detectors, SCA detectors, FM deemphasis, etc. -- all replaced by software code. Furthermore, this code can be reprogrammed as needed to change operating
parameters, to fine tune performance or to accommodate new features.
Offering vastly superior station separation, the digital IF filter has automatic, dynamic bandwidth control that adapts instantly and continuously to changes in the signal. In addition, the shape
of the IF bandpass has a steep, almost vertical roll-off (see below), compared to the broad, bell-shaped curve of a less selective conventional filter.
To further take advantage of the digital environment, DigiCeiver has digital loudness and tone controls, and some models will have digital parametric equalization. In specific OEM and aftermarket
applications, these equalizer settings could be factory- or dealer-optimized to match the acoustic personality of the car.
DigiCeiver offers superior performance without the high costs associated with premium conventional tuners. While functional tuners can be made quite cheaply (and usually are), high performance
analog tuners require very careful design and expensive low-tolerance parts. Each individual circuit in each individual radio must be electrically aligned and calibrated in order to even approach the
performance of DigiCeiver.
Blaupunkt DigiCeiver Technical Information
Figure 1. DigiCeiver System Block Diagram
As a result of advanced high-integration strategies, the complete functionality of a top-level car radio has been reduced to a two-chipset. The digital IC performs the following functions: A/D
conversion at the IF-level, IF filtering, AM/FM demodulation, stereo and RDS decoding, RDS error correction, tone control, D/A conversion at audio frequencies, and volume control. It contains
additional inputs for both analog and digital sources plus a communications interface for digital signal processing.
Figure 2. Automatic, Dynamic Bandwidth Control
Based on highly advanced chip design, digital technology produces optimum reception quality. Digital IF filters provide superior performance compared to conventional technology. Among their
dominant characteristics are: nearly perfect rectangular shape, complete symmetry, no group velocities, and total independence from component tolerances and temperature variations. Automatic, dynamic
bandwidth setting improves reception in the event of interference from neighboring stations.
Figure 3. Reception Characteristics
Good signal-to-noise ratios over large variations in input field strength together with extremely low third-harmonic distortion lead to exceptional reception and superior sound.
Figure 4. Parametric Sound Shaping
The integrated 2-band parametric equalizer enables amplification/attenuation of +/- 20 dB in two wide frequency bands with user-defined Q-factors. In a typical application, a specific set of
user-selectable settings is programmed from the options illustrated above. The following three figures demonstrate the specific uses of the Parametric equalizer.
Use the low frequency equalizer to add an additional boost to the bass frequencies.
If your vehicle resonates at a certain bass frequency (vibrates), then you can use the equalizer to cut the specific frequency.
For vehicles that both accentuate and absorb sound, and to make up for speakers that are not placed in the best position, the proper adjustment of the parametric equalizer can reduce the variance
from the perfect flat reproduction.TD>
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