TABLE OF CONTENTS When designing precision analog circuits, it is critical that users avoid the pitfall of poor passive component choice. In fact, the wrong passive component can derail even the best op amp or data converter application. This section includes discussion of some basic traps of choosing passive components.
So, you have spent good money for a precision op amp or data converter, only to find that, when plugged into your board, the device does not meet spec. Perhaps the circuit suffers from drift, poor frequency response, and oscillations or simply does not achieve expected accuracy. Well, before you blame the device, you should closely examine your passive components including capacitors, resistors, potentiometers, and yes, even the printed circuit boards. In these areas, subtle effects of tolerance, temperature, parasitics, aging, and user assembly procedures can unwittingly sink your circuit. And all too often these effects go unspecified (or underspecified) by passive component manufacturers.
In general, if you use data converters having 12 bits or more of resolution, or high precision op amps, pay very close attention to passive components. Consider the case of a 12-bit DAC, where 1/2 LSB corresponds to 0.012% of full scale, or only 122 ppm. A host of passive component phenomena can accumulate errors far exceeding this! But, buying the most expensive passive components will not necessarily solve your problems either. Often, a correct 25-cent capacitor yields a better-performing, more cost-effective design than a premium-grade (expensive) part. With a few basics, understanding and analyzing passive components may...
