Considerations for PCB Board Design
In high-speed analog signal chain design, printed circuit board (PCB) wring and layout require careful considerations. In this article, EPCB will begin with the description of exposed pads, followed by layer capacitance and ground separation.
The exposed pad (EPAD) is sometimes overlooked, but it is very important for the full use of the signal chain performance and adequate heat dissipation of the device. EPAD, called pin 0 by ADI company, is the pad used under most of today's devices. It is an important connection where all internal ground of the chip is connected to the center point below the device. It is important to solder the pin to the PCB board so as to achieve reliable electrical and thermal connections.
Engineers sometimes may ignore the purpose of using decoupling, merely dispersing many capacitors of different sizes on the PCB board, and connecting the lower impedance power supply to ground. How much capacitors are needed? Many related documents indicate that many capacitors of different sizes must be used to reduce the power transmission system (PDS) impedance, but this is not entirely correct.
The question most frequently asked by analog signal chain designers is: Should the ground plane be divided into AGND and DGND ground planes when using an ADC? Though it depends on the situation, but usually not separated. Why not? Because in most cases, blindly separating the ground plane will only increase the inductance of the return path, and it will do more harm than good.