When designing any electronics that consume a significant amount of power, you need to consider where that power will go. With power electronics –such as IGBTs, power FETs, or power transistors – you might be expecting most of it to end up in your load, but there will be some which don’t. Even devices that […]
Transimpedance amplifier signal-to-noise
The use of opamps as a transimpedance amplifier is well known and a good analysis of the noise behavior of them is in the old Burr Brown Application Bulletin AB-076 from 1994. This is still available from Texas Instruments’ website as sboa060 – simply search for that on their website. Improving the signal to noise […]
Improving transimpedance amplifiers with a bootstrap
Analog bootstrap circuits are traditionally ones where output is fed back to the input, usually to increase input impedance. This can be to minimize either the resistive or reactive (usually capacitive) components of the input impedance or both. The term is now also used with MOSFET drivers where a capacitor is charged and used to […]
Input bias current cancellation in bipolar op amps
Bipolar operational amplifiers have an essential input bias current requirement. This bias current has to come from somewhere and can be a nuisance in some types of high impedance circuits such as charge amplifiers and transimpedance amplifiers and can result in offset voltages where input resistances aren’t matched. The example shown below has an input […]
MOSFET Drivers – what are they and why do we need them?
There are a lot of MOSFET drivers around these days. MOSFET drivers often contain MOSFETs themselves. There are several reasons for needing MOSFET drivers: Drive current – MOSFETs can have very high gate capacitance. For example, the IRF530NS from International Rectifier is a 90mW device which can withstand 17A continuous drain current at 100V and […]
Choosing, using, and designing oscillators
Most electronics today have oscillators in them. Digital circuitry needs a clock. Radio frequency signals require an oscillator or clock. Some analog circuitry also needs a clock or oscillating signal source. If you are using a microcontroller then it might have a built-in clock, although it may not be accurate enough, depending on your application, […]
Analog vs Digital
I am principally an analog designer who also designs custom ICs, but I also get involved in microcontrollers, and CPLD/FPGA design when necessary, which is quite often. Some applications are often clearly digital or analog, but others are not so clear. Which approach you take is likely to depend on your skill-set. A digital engineer […]
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 […]
SPICE: how to choose an analysis
SPICE is a very useful tool when used correctly and is used far beyond its original purpose — “Simulation Program with Integrated Circuit Emphasis.” It is now used for simulation of many non-integrated circuits. However, whichever type of circuit you use it for, you need to be aware of its limitations. The modeling has been […]
How to make floating point measurements that count
Sometimes you need to make a “floating” measurement of a current or voltage. By “floating” I mean that you want to measure a voltage across something (or current through something) where neither end of the voltage are ground (0V). While one input being referenced to a supply rail other than 0V isn’t strictly speaking “floating,” […]