Building a DVB Tuner System with Kaben's Products and Technology The Digital Video Broadcast standard delivers signals which provide HDTV (High Definition TV) quality signals. Unlike the old Standard Definition TV signals, the HDTV signals occupy a bandwidth of 8 MHz. These signals can be delivered to the TV receiver through either Cable channels, standard Terrestrial (wireless) channels, Satellite channels, or Hand-held (portable wireless) channels. Each of these delivery methods uses a form of Quadrature Amplitude Modulation or Phase Shit Keying modulation to carry the data signal. Specifically, DVB-C employs one of 16 QAM, 32 QAM, 64 QAM, 128 QAM, or 256 QAM; DVB- T uses either 16 QAM, 64 QAM or QPSK; while DVB-S uses one of 16 QAM, QPSK, or 8PSK. Further, each delivery method has a different set of issues.
Cable reception has a large number of available channels to choose from, resulting in a potentially high intermodulation level and creating excessive interference. Terrestrial reception is vulnerable to the classic near-far channel problem, where the desired channel has a low power level reception, while an undesired, adjacent channel has a high power level. Unlike Terrestrial reception, Satellite reception does not suffer from a high near-far channel problem, but it does have a large number of available channels, and has the same intermodulation difficulty as Cable reception. Finally, Hand-held reception is challenged by the low power consumption requirement common to all portable devices.
Kaben has invented a wholly new type of RF filter based on RF sampling techniques. This SIF (Sampled IF Filter) can be integrated with the other blocks of the DVB tuner onto a single silicon die, thereby removing the need for, and extra cost of, external components. This filter not only achieves excellent (SAW like) filtering performance, it is exceedingly robust to semiconductor process variations, and temperature changes. Further, the filter is programmable in bandwidth and center frequency, enabling adaptive reception to different TV channels. Inclusion of this novel RF filter into a TV tuner significantly reduces the cost of the BOM (Bill of Materials). Further, for the first time, it enables a TV tuner to be integrated as a secondary function onto a CMOS die, with the host function being, for example, a DVB back-end processing chip.
The Kaben DVB tuner integrates the DVB tuner functions while addressing the issues for the Terrestrial, Cable, and Satellite channels, while the Kaben Low Power DVB tuner addresses the challenges of achieving low power consumption in a Hand-held application.
The Kaben DVB tuner is shown in the diagram where the multiple available channels are delivered in a band stretching from 50 MHz to 860 MHz. For Satellite channels, a millimeter wave LNB unit proceeds the tuner. For Terrestrial channels and Hand-held channels, the signals are first directed to an off-chip Switchable, Continuous Time filter which provides some light filtering to help address the near-far channel problem.
The complete band is then amplified in an LNA having a delayed AGC, and passed to the first SIF. This first SIF is tunable over the complete broadcast band extending form 50 MHz to 860 MHz, and has a passband bandwidth of 80 MHz, thereby passing 10 adjacent channels, including the desired channel, at a time. The desired channel need not be centered in the passband; in fact, for Terrestrial and Hand-held channel service, the first SIF should be tuned to include the desired channel, while also rejecting at least the closest, high power, undesired channel.
To tune over the band of 50 MHz to 860 MHz, the first SIF is clocked with a synthesizer having a VCO running at 10 GHz. The 10 selected channels emerge from the first SIF in a sampled-analog IF form, are amplified (buffered) in a gain stage, and directed to the second SIF. The second SIF isolates the desired channel and passes it, at 36 or 44 MHz, and still in sampled-analog form, to the second AGC amplifier. Finally, the sampled-analog desired channel is converted to analog form for connection to the television's back-end analog circuits for channel equalization, demodulation, error correction, encoding etc.
The first SIF band selection, and the synthesizer clock frequency, are determined by the channel select and control logic. The exact group of 10 channels to be passed by the first SIF, and the corresponding clock frequency to be generated by the synthesizer, is dependent on the presence of near channels having excessive power levels (as will occur in Terrestrial and Hand-held services, but not in Cable or Satellite services). The presence and channel frequency of all high power channels is determined by sensing, intermittently, the power level at the output of the first SIF.
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