Dynamic range improvement through ground noise control in a data communication equipment

Present day data communication equipment use essentially a combination of digital ICs (both LSI and VLSI), analogue circuits and A/D and D/A converters. The requirement of small size and light weight also imposes space constraints. In view of these requirements, equipment designers use fewer printed circuit boards to pack these circuits. In such applications the planning of the grounding scheme is essential for obtaining the maximum dynamic range of the system. Equipment which were designed and developed at LRDE uses three PCBs in which a power supply, (DC-DC converter), a data processing unit, A/D and D/A converters, a microcontroller and a modem are used. Approximately 50 ICs are used in the equipment, and they are arranged on two PC boards. To begin with the digital ground, analogue ground and power supply ground are mixed up. As a result of this the measured ground noise of the digital circuits varies from 25 mV to 60 mV on the PCB, and the dynamic range of the receiver is -40 dBm. At this juncture, the grounds are properly isolated and reconnected. This has resulted in an improvement in the noise and subsequently the dynamic range. The paper highlights, step by step, how this range improvement was obtained by rearranging the ground connections. It also highlights the test procedure that is adopted to ascertain the dynamic range improvement