GATES TO FPGAS: TTL ELECTRICAL PROPERTIES

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On the path to exploring complex logic, let’s discuss the electrical properties that digital logic signals are comprised of. While there are many types of digital signals, here we are talking about the more common voltage based single-ended signals and not the dual-conductor based differential signals. Single-ended Logic Signal I think of most logic as being in

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WIRE WRAP 101

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You might notice that many of my writings start with “Back in the day”. Not wanting to disappoint I will say that back in the day we used to use wire wrap technology when we needed a somewhat solid, somewhat reliably assembly. Given a readable schematic a good tech could return a working or near-working unit in a day or two depending on the completeness and accuracy of the schematic.

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FROM GATES TO FPGA’S – PART 1: BASIC LOGIC

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It’s time to do a series on logic including things such as programmable logic, state machines, and the lesser known demons such as switching hazards. It is best to start at the beginning — but even experts will enjoy this refresher and might even learn a trick or two. I’ll start with logic symbols, alternate symbols, small Boolean truth tables and some oddball things that we can do with basic logic. The narrative version is found in the video, with a full reference laid out in the rest of this post.

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Tech Note on Op-Amps Driving Capacitance

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A great tech not on OP Amps driving capacitance. http://www.analog.com/library/analogDialogue/archives/31-2/appleng.html

Q. How does capacitive loading affect op amp performance?

A. To put it simply, it can turn your amplifier into an oscillator. Here’s how:

Op amps have an inherent output resistance, Ro, which, in conjunction with a capacitive load, forms an additional pole in the amplifier’s transfer function. As the Bode plot shows, at each pole the amplitude slope becomes more negative by 20 dB/ decade. Notice how each pole adds as much as -90° of phase shift. We can view instability from either of two perspectives. Looking at amplitude response on the log plot,circuit instability occurs when the sum of open-loop gain and feedback attenuation is greater than unity. Similarly, looking at phase response, an op amp will tend to oscillate at a frequency where loop phase shift exceeds -180°, if this frequency is below the closed-loop bandwidth. The closed-loop bandwidth of a voltage-feedback op amp circuit is equal to the op amp’s bandwidth product (GBP, or unity-gain frequency), divided by the circuit’s closed loop gain (ACL).

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New Instrumentation Amp

Instrumentation Amp ICON

We used to build amplifiers for digital scales (weighing Instrumentation)  where we would sample a full scale voltage reference and a ground reference and from there digitally cancel out gain and baseline drift.  Nowadays the amplifier itself can do a lot of this correction.  We used to call these amplifiers “coppers” referring to the process

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Thermocouple Amplifiers

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I just did a video for Hackaday about Thermocouple Amplifiers, a quickie video feature Linear Technology in this case.  The spares from the build for the video are available at http://www.herdware.com/shop/analog/thermocouple-amplifier/ along with a Type K Thermocouple. From the Hackaday video Thermocouple is a terrific way to measure temperature. The effects of temperature change on dissimilar metals

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