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Last post we examined the Sallen-Key topology, now we get into a specialty device, namely the instrumentation amplifier. Typically constructed from several amplifiers, it has proven so effective in amplifying low-frequency differential voltages, it’s now widely available in pre-packaged form. In this case the signal being amplified is of very […]

Cooking with Op-Amps, part 12: Instrumentation Amplifiers!


We have so far stuck to the simplest cases of filters, often single-pole; is a band pass/stop filter two poles? Technically yes, but the term usually expresses the idea that both poles affect the same pass/stop frequency together, doubling the rate of attenuation. In other words, where a single pole […]

Cooking with Op-Amps, part 11: Sallen-Key Filters!


Last time around we built a simple (single-pole) high-pass filter, this time it’s band pass and band stop. One is the opposite of the other, with the frequency cut-off points adjusted accordingly; schematically they’re a little different looking though. Band-Pass This one’s the easier of the two because it’s a […]

Cooking with Op-Amps, part 10: Band Pass/Stop Filters!



Last time we looked at low pass filters, this time high-pass; it’s opposite day. We also take a brief look at capacitor types, as they are critically important to filter design. High Pass High-pass filters are encountered a little less frequently than the basic first-order low-pass, but they do have […]

Cooking with Op-Amps, part 9: High-Pass Filters!


Last time around, we embraced failure in wilfully destabilizing an op-amp. This time, we look at filters. We use a filter when only some frequencies of input signal are desired. The subject of filters is huge, and there’s no way to cover it exhaustively in a blog post. We can, […]

Cooking with Op-Amps, part 8: Low Pass Filters!


Last time we looked at configuring an op-amp with negative feedback, but with enough reactive (phase shifting) components to make it unstable. The trouble with the amplifier of choice is that it’s a very low-bandwidth part, intended for use amplifying slow or nearly DC signals. The size of components required […]

Cooking with Op-Amps, part 7: Test it!



Last time around we explored setting gain in inverting and non-inverting configurations, and how phase affects performance. This time, we embrace failure, in theory. We learn more when things go wrong, and an unstable amplifier could be classed as having gone wrong. Instead of waiting like lambs for the (ahem) […]

Cooking with Op-Amps, part 6: Make it Fail!



So far we’ve covered input impedance, output impedance, offset voltage, and talked a little noise; so what’s left? It gets more interesting as complexity increases; this time around it’s about gain, and a first look at using feedback to close the control loop. This is one of those weird areas […]

Cooking with Op-Amps, part 4: Gain Bandwidth Product.



Previously we looked at the inputs, what they look like inside the amplifier, and the differences between ideal and real behaviour. This time we look at what comes out the front end of the amplifier. When hooking up a source (power supply / battery / amplifier) to a load (appliance […]

Cooking with Op-Amps, part 3: Output Impedance.