When you need current and voltage

-October 01, 2005

In Current Sources & Voltage References, Linden Harrison explains how to design these essential circuits.

Need a stable reference voltage? Just get a zener diode and a resistor. Need a stable current source? Add a transistor and another resistor. That may be all you need, but circuit design isn't always that simple. For everything else, you'll benefit from reading Linden T. Harrison's book.

I've never seen a book devoted to these workhorse and often-overlooked circuits. Current Sources & Voltage References teaches you how semiconductor devices work and how to use them to design stable voltage and current sources. The author also gives you some history about the people that designed the early devices and circuits.

Harrison divides this book into the two topics, starting with current sources. For each of the two topics, he starts with semiconductor physics, moves on to device characteristics, and then on to circuit applications that build in complexity. He provides plenty of circuit examples, and he clearly explains how to use bipolar transistors, JFETs, MOSFETs, IC voltage references, and matched devices in your designs. Harrison also spends several chapters covering classic devices such as National Semiconductor's LM134 current source and new devices such as the Advanced Linear Devices' ultra-low threshold CMOS transistor array, the ALD1107.

The book's application circuits go beyond the book's title. For example, Harrison explains how to use a voltage reference as a temperature sensor—the device's voltage is proportional to temperature. He also provides circuits that combine current sources with digital-to-analog converters to form a digitally controlled frequency source. (Disclosure: The book's publisher is owned by Test & Measurement World's parent company.)

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