Efforts at the Bureau of Standards 110 years ago paved the way for the cold-junction-compensation technique used today. Thermocouples have long been used to make temperature measurements. They are simple, consisting of a pair of wires of dissimilar metals welded together at one end. They are rugged, operate over wide temperature ranges, and generate readily […]
What is jitter and what can I do about it (part 2 of 2)?
Operations on acquired jitter data help quantify jitter values. Part 1 of this article described the oscilloscope eye diagram and unit interval (UI) and focused on a single ideal rising edge with 28 additional edges representing some degree of jitter (Figure 1). We determined the peak-to-peak jitter to be 15 ps, based on the edges […]
What is jitter and what can I do about it (part 1 of 2)?
Measuring and quantifying jitter are the first steps toward controlling it. Jitter is a measure of the timing performance of a digital data stream such as Ethernet, USB, PCIe, or HDMI. It defines when data transitions occur in relation to an ideal waveform. Excess jitter can lead to signal-integrity problems that result in high bit-error […]
What is GPIB and is it obsolete?
The bus, codified as the IEEE 488 standard, continues to find use in legacy test-system upgrades and in calibration labs. The General-Purpose Interface Bus (GPIB) began life as the Hewlett-Packard Interface Bus (HP-IB). Hewlett-Packard, whose electronic test-and-measurement business has evolved into today’s Keysight Technologies, created the interface in the 1960s to connect multiple instruments in […]
What is de-embedding and how do I perform it (part 2)?
When testing a device in a fixture, you can use transfer scattering parameters (T-parameters) to help remove the fixture’s contribution from your measurement result.
What is de-embedding and how do I perform it (part 1)?
It’s a tenet of the test-and-measurement industry that you should concentrate on looking for defects in your device under test (DUT) — not in your test equipment. Figure 1 illustrates a common problem. An instrument presents an incorrect reading; in this case, an LRC meter or multimeter presents a resistance reading that’s about 5% low. […]
What are insertion loss and return loss and how can I measure them?
These basic RF measurements often uncover system problems in wired and wireless communications. If you observe a signal traveling from a source to a load through a passive system of some sort, you will notice that the signal attenuates by the time it reaches the load, and you will also notice that some of the […]
What is the MIPI I3C interface and where might I use it?
I3C improves on I2C through higher speeds and backward compatibility You’ll often want to interconnect two chips on a circuit board, and a standard interface can help you design efficiently. Engineers working at a division of Philips thought so back in 1982, so they developed the Inter-Integrated-Circuit interface, which they dubbed I2C. Of course, things […]
What is an instrument driver and why do I need one?
Instrument drivers take some of the sting out of controlling test instruments by adding an abstraction layer. Almost everyone who uses computers has had experiences with drivers, and probably not good ones. In the olden days, if you had wanted to hook an old printer up to a new computer, you would have searched through […]
What is a Smith chart and why do I need one? (Part 2)
Take a journey around a Smith chart to find capacitance and inductance values in a matching network. Before computers became ubiquitous, the Smith chart simplified calculations involving the complex impedances found in RF/microwave circuits such as the one shown in Figure 1. That circuit includes a source with impedance Zs, transmission line with characteristic impedance […]
