Chapter 23 - Circuit Board Layout Techniques

Abstract

This chapter discusses the points one should consider while designing a printed circuit board (PCB) for analog circuitry. The PCB layout for analog circuitry must be designed such that the effect of the PCB is transparent to the circuit. Any effect caused by the PCB itself should be minimized so that the operation of the analog circuitry in production is the same as the performance of the design and prototype. Noise is the primary limitation on analog circuitry performance. While structuring board structure, one should use a high quality board material, such as FR–4 and multilayer boards are as much as 20 dB are better than double sided boards. Placement of power and ground planes should be interior of the board instead of the exterior. While routing one must keep analog circuitry close to the power connector of the board and also make sure that traces to the inverting and noninverting inputs of the op amp do not parallel each other for any significant length. It is better to avoid vias, but the self-inductance of vias is small enough that a few should cause few problems. At bypassing one should use the correct type of capacitor to reject the conducted frequency range. Tantalum capacitors should be used at power input connectors for filtering power supply ripple. Using ceramic capacitors at the power connections of every op amp IC package is a better practice. Further, add series inductors or resistors for stubborn cases and bypass analog power only to analog return, never to digital return.