A Note From the Editor

Welcome to the November issue of Analog Dialogue.

It’s November and the days are becoming shorter, the weather is foggy and wet, and this year’s garden work is nearly done. This is the time of the year I look forward to spending time in my lab. Besides repairing electronic equipment (currently a Denon 4306 receiver with a digital part that does not work), I like to experiment with sensors. Surprisingly, and I’m not sure how I couldn’t have previously known this, I was unaware that a simple diode has a temperature dependency of about 2 mV/°C. Fortunately, this month’s StudentZone article provides more details and explains how to build a simple differential temperature sensor. Sure, I could use a general-purpose sensor, but why not try the experiment? Let me know if your experiment was as successful in your lab. 

Another sensor of interest to try and verify will be the AMR sensor, as mentioned in this month’s first article. It features brushless dc motors, which, as the name suggests, have no brush contacts. Motor position sensors are required to measure the position between the stator and rotor to ensure the correct stator coil energizing sequence. Traditional Hall switches are used for this function. They can now be replaced by an elegant application using a magnetoresistive angle sensor positioned in front of a bipole magnet mounted onto the end of the motor shaft. This enables applications like electrical power steering, which once used mechanical solutions.

Our second article is a continuation of last month’s topic on optimized sigma-delta modulators for current measurement in motor control applications. Part 2 continues with the discussion of a new sinc filter structure that improves measurement performance in motor control applications. This is followed by a discussion on the implementation of sinc filters with HDL code for optimum performance and, finally, measurement results from an FPGA-based 3-phase servo drive are presented.

Quite often a bipolar dual power supply is required in many applications, and these use linear regulators. For years I have been using the LM780x and LM790x in my lab for such purposes. However, there are two disadvantages to this including power loss within a linear regulator and the necessity to use two ICs. A better solution would be to use a single switching regulator that produces both outputs from a relatively high input, at good efficiency, low EMI, and good regulation. This next article presents two elegant circuits that generate ±12 V outputs from a wide 30 V to 400 V input voltage range. One circuit utilizes an isolated flyback topology, while the other is based on a nonisolated buck topology.

In our Rarely Asked Questions article, we ask: “Is it possible to increase the gain of a fixed-gain difference amplifier?

The classic 4-resistor difference amplifiers solve many difficult measurement problems. Quite often an integrated solution (with the four resistors on the die) is a preferred solution, as matching of resistors in a difference amplifier directly affects the performance of the application. Such differential amplifiers with integrated resistors have a disadvantage if a different gain setting is necessary. If more gain is required, typically another amplifier stage is added. Providing a positive feedback path by simply adding a few resistors to the fixed gain amplifier will reduce the overall negative feedback and therefore result in a higher overall gain.

Our StudentZone ADALM2000 series continues with diodes. This time you will use a diode as a temperature sensor. The sensitivity of a diode is about 2 mV/°C, as a simple resistor with some kΩ or a current source will bias a diode. Using a second diode, we are able to measure the temperature difference between two temperatures; hence a differential temperature sensor could be made with two diodes and two resistors.

And as we have for 53 years, we invite you to be part of the dialogue in Analog Dialogue. You can get in touch through our blogFacebook page, or email. Let us know how we’re doing and what you’d like to see from us in the coming months.