When designing low noise circuits – signal conditioning circuits, amplifiers or analog to digital converter interfaces, for example – SPICE simulation can be helpful in ensuring you have a low noise solution, particularly where signal conditioning circuits are high gain. Input referred or output noise? One decision you need to make in noise analysis is […]
Demystifying SPICE noise simulation
While I have covered the basics of noise simulation in SPICE before, I thought it was worth revisiting the subject to show some of the confusing results you can sometimes get and how to interpret them. The example I used earlier, a simple opamp based amplifier, didn’t show any unusual noise results but other circuits […]
Photodiode: light sources, the amount of light, and color
I have touched on light sensing methods and the amplification of the signals from them in the past, but at a more fundamental level, how do you choose one? What parameters are important? The answer depends, among other things, on the light source (focused or not), the amount of light and its color. Focused or […]
Mechanical vibration for electronics: the quartz crystal
It is now 100 years since Alexander Nicholson at Bell Telephone Laboratories built and patented the first crystal oscillator, and crystals are still the main source of accurate oscillations up to UHF frequencies using quartz instead of Rochelle Salt (see US patent 2212845). Quartz crystal oscillators use the piezoelectric effect. The piezoelectric effect refers to […]
Are your op amps pumped?
I was recently thinking about the issues surrounding rail to rail input opamps and the problems of making them low distortion – a problem I have had to overcome when designing integrated circuits for instrumentation applications. Some rail to rail opamps use two input stages – one using NMOS input transistors, the other using PMOS […]
How much math do you need to know to design electronics?
Education for electronics design tends to have a fair amount of math in it but how much is really required nowadays in order to design electronics? You certainly need some, but a high percentage of what you learn at college or university is likely to be unused once you leave, although this does depend on […]
Interfacing and using bridge sensors
Sensors such as strain gauges, pressure gauges and some magnetic sensors are often bridge devices. They can be full or half bridge although the bridges are usually made of multiple devices connected together, with MEMS sensors being an exception. So, in the case of a strain gauge, a half bridge would be made with one […]
Signal line and supply filtering
There are many reasons for needing to filter power supply or signal line. Power supply lines from a switching regulator may be too noisy for sensitive analog circuitry. Signal or power supply lines may pick up interference either from the rest of the system circuitry or from external devices. With signal lines the problem of […]
Troubleshooting analog circuits
While you may need to troubleshoot a circuit that used to work and now doesn’t, the emphasis here is how to troubleshoot a design when you have your first PCB made. While you may be fortunate and everything works perfectly first time, there is often a need for some troubleshooting with a new design. The […]
Using and interfacing to thermocouples
I recently had cause to look again at thermocouples after not having used them for many years. While they may seem a little old fashioned when you can measure temperature with a simple IC or a complex IC with an I²C or SPI interface such as the Analog Devices ADT7410, thermocouples still have their uses. […]
