HP 34970A Loading Errors Due to Input Bias Current

Chapter 8 Tutorial

Measurement Fundamentals

Loading Errors Due to Input Bias Current The semiconductor devices used in the input circuits of the internal DMM have slight leakage currents called bias currents. The effect of the input bias current is a loading error at the internal DMM’s input terminals. The leakage current will approximately double for every 10 °C temperature rise, thus making the problem much more apparent at higher temperatures.

RS

	HI
			Ci
VS		Ib Ri		DMM
	LO

Where:

Ib = DMM bias current

Rs = DUT source resistance

Ri = Input resistance (10 MΩ or >10 GΩ)

Ci = DMM input capacitance

Error (V) = Ib x Rs

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