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Article: Single IC forms inexpensive inductance tester.(design ideas)
- Article from:
- EDN Asia
- Article date:
- November 1, 2007
- Author:
CopyrightCOPYRIGHT 2007 Reed Business Information, Inc. (US). This material is published under license from the publisher through the Gale Group, Farmington Hills, Michigan. All inquiries regarding rights should be directed to the Gale Group. (Hide copyright information)
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This Design Idea shows how to build a reliable, low-cost, and simple inductance tester. The basis for the tester is a Pierce buffered CMOS oscillator (Figure 1). Instead of using the usual quartz crystal, you connect the inductor under test. This oscillator uses a single CMOS inverter biased through resistor [R.sub.1] in its linear region to form a high-gain inverting amplifier. Because of its high gain, the inverter dissipates lower power than an unbuffered gate; even a small signal drives the output high and low.
The LC[pi] network forms a parallel resonator that ideally resonates at the frequency [f.sub.0]=1/ 2[pi][square root of ([L.sub.x] [C.sub.s]) which ...