Most of the pitfalls of integrating a DAB receiver into an existing or new motherboard/chassis are overcome by using a sub-system DAB module - for example, the RS300 module, which also integrates low-power RF signal circuitry and a CD control interface.
Basic rules
System performance can be maintained by paying close design attention to the RF section, power supply regulation and digital noise coupling, from the mix of analogue and digital sub-sections. RadioScape modules offer sensitivities of better than -98dBm, a system parameter that is expected from a good receiver. The majority of system architecture problems that reduce sensitivity are lack of ground-plane, dirty power rails and bad digital signal control. To enable the antenna to perform correctly, it is essential to maintain the input impedance of the RF Section (50 Ohm) by using a good ground plane. Typically, telescopic whip antennas (for FM) are used at l/4 (for DAB) where the reflective component from a good ground plane makes the physical size the electrical equivalent of l/2. This is the point where maximum power transfer into the RF receiver can occur and is the best practical arrangement for a DAB and FM tuner. Maintaining good power supplies to the receiver components is also a key factor, ensuring ground effects are minimised with good decoupling and regulation. Care must be taken when using switching regulation techniques, as selfinterference (i.e. transmission of spurious frequencies generated by the receiver) can limit sensitivity drastically. Reducing the digital coupling into other parts of the system will aid for good design practices. LCD panels, graphics display, memory card interfaces and rotary encoders are all sources of digital noise sources. These devices, by their nature, have fast switching digital signals, with sharp edge transitions and high average spectral power.Digital signals are comprised of a sine wave as the fundamental wave plus many of its harmonics, expressed by Fourier analysis. Such signals inherently are excellent noise generators, radiating from even the smallest tracks, which form parasitic antennas, adding to any self radiating noise. Applying basic design techniques of short cabling (tracking) and slowing down the rise/falall time of the digital lines, by adding capacitors to ground are very effective measures. This technique can be coupled with a reduction of the power that is being transferred in the digital signal, by adding series resistance. This forms a low-pass filter at the source of the digital signal. As logic dictates, these measures are most effective at the source of the digital waveform. Once the manufacturer has succeeded in integrating the analogue and digital components whilst maintaining system performance, the next stage of evolution is the development of an intuitive user interface.Radioscape addresses this function in software, where scaleable user interfaces can be crafted quickly, from simple 2 line by 16 character displays, to graphical display capability and colour displays in the future. The experience of digital radio is not only «audio" but also visual, with current information being received as part of the receiver capability. One such example is the Electronic Programme Guide (EPG), where more sophisticated displays offer a more enriched user experience.As DAB technology advances at a fast pace, it is becoming more apparent that having the ability to maintain the same hardware while upgrading the software is becoming a key driving force for the ever faster pace of consumer demand. The RS300L offers a generic DAB decoding platform, with multi-data decoding capability and advanced peripheral support. This includes Graphics Displays, solid state memory devices and USB interoperability. RadioScape products are derived from a common philosophy, abstract to a high enough layer, where hardware becomes general purpose and software defines the product feature and capability, thereby reducing the time-to-market and ensuring a growth line from the same foundation of hardware. Simply put, this is the era of Software Defined Radio, where the system is engineered from the software perspective and is turning the development of DAB products inside out.
