Development of a New Frequency Synthesizer for Terrestrial Digital Television Broadcast Tuner by Fujitsu
In Japan the tuners that are incorporated into the TVs and mobile phones receive radio signals from broadcast towers, where the tuners will extract audio-visual data from those signals. The tuners employ frequency synthesizer capable of generating a clock signal that are equivalent to the frequency of the channel the viewer is selected to watch. The need of the frequency synthesizer within the tuners is due to thee fact that each channel which is transmitted by a broadcast tower occupies a different frequency. Terrestrial digital TV broadcast in Japan consists of 14 segments occupying 6 MHz of bandwidth. 12 of these segments are designated for TV, one for “1seg” broadcast for mobile phone, and the remaining one segment is left empty.
Therefore, channels are spaced by 3/7ths of 1 MHz. As a result of this, the frequency synthesizer needs to generate a clock signal at 3/7th MHz intervals in order for all channels to be received. 1seg broadcasting which is viewed via mobile phones is gaining popularity, making the manufacturers of the mobile phone to incorporate terrestrial digital TV broadcast tuners which are both compact in size and operates at a low power. Furthermore, there is growing expectation for mobile phones that are equipped with dual-tuners which are capable of simultaneous recording of multiple TV programs along with quicker channel scanning. Normally, the synthesizers as the major components of the tuners typically use delta-sigma modulation in fractional multiples method, where external filter circuit to suppress the noise that can impair the tuner’s reception sensitivity is required. Need for such external filters is an obstacle in miniaturization effort of the module. The issue becomes more apparent in creation of dual-tuner, where two such external filters are required. To overcome this technical challenge, Fujitsu has developed a new frequency synthesizer designed for reception of terrestrial digital TV broadcasts which uses a Circulating Register modulator which has lower noise that conventional delta-sigma modulators. The new frequency synthesizer’s circulating registers modulator features an innovative circuit design whereby seven registers are lined up in parallel ,resulting in accurate reception of 3/7th MHz frequency intervals that are used in terrestrial digital TV broadcast in Japan. the new technology by Fujitsu eliminates any needs for external components for frequency synthesizer, thus reducing the circuit size to 1/3rd in comparison to previous circuits. The new technology is a step forward in realization of compact dual-tuners for mobile phones.