Analog Comparator Circuit Design A comparator answers a question: is the input above the reference or below it. It is often implemented with an operational amplifier, and that is the first mistake, because an amplifier and a comparator are optimised for different things. Why Not an Operational Amplifier An operational…

Thermal Simulation And CFD For PCB Designs A thermal simulation predicts how hot a circuit will run before the board exists. It answers two questions that a calculation on a datasheet cannot: how much of the heat leaves through the copper rather than through the package, and how much the…

RMS to DC Converter Circuit Design An RMS to DC converter produces a voltage proportional to the heating power of a waveform, which is the quantity that matters for a load. Average responding meters give the right answer only for a sine wave, and a true RMS converter gives it…

Vibration Fatigue Of Solder Joints A board that is mounted in an enclosure and exposed to vibration behaves as a plate with a mass attached to it, and the solder joints are the smallest and most highly stressed part of the structure. The loads are small compared with a drop,…

Sample and Hold Circuit Design A sample and hold circuit captures an input voltage and holds it steady while a converter or a multiplexed system uses it. It is the answer to a source that cannot settle in the time available, and its own errors are a different set from…

Peak Detector Circuit Design A peak detector follows a signal upwards and holds the highest value it has reached. It is used to measure an amplitude, to capture a transient and to drive an automatic gain control, and its accuracy depends on how the diode drop and the droop are…

Cable Shield Termination And Grounding A cable that enters an enclosure is a conductor with a shield around it, and the shield only works if it is terminated correctly. A shield that is connected at one end and left open at the other is an antenna, a shield that is…

Adhesives for Component Bonding and Staking Adhesive does jobs that solder cannot. It holds a heavy component on the underside of a board before the second reflow, it stakes a tall part against vibration, and it bonds a heat sink or a stiffener where a joint would not be appropriate.…

Silkscreen Legend: Preparation, Placement and Process Control The silkscreen legend is the only documentation that stays with the board after it leaves the design office. It tells the assembly operator where each part goes, it tells the inspector what the board should look like, and it tells the repair technician…

Immersion Tin: Design Rules and Process Limits An immersion tin coating is deposited on copper by a displacement reaction, in which tin ions in solution replace copper atoms on the surface. The result is a thin, flat, matt layer of pure tin that protects the copper and provides a solderable…