Application Note 253: 2001 Printer Port Controls Curve Tracer

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Application Note 253: 2001 Printer Port Controls Curve Tracer

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CONVERSION/SAMPLING CIRCUITS MEASUREMENT CIRCUITS
Application Note 253: 2001
Printer Port Controls Curve Tracer
This article describes curve tracer circuit that uses computer display control. circuit controlled parallel port. Software provided, written BASIC, control measurement display results monitor. When connected printer port circuit shown Figure enables determine current-voltage (I-V) characteristics active component integrated circuit. short BASIC program* drives port displays characteristic graph monitor. result very useful diagnostic tool fault analysis.
Figure 12-bit serial-data (IC4) (IC3) form interface that enables printer port control this curve tracer. 12-bit digital-to-analog converter (DAC), IC4, configured bipolar outputs ±2.048V. Op-amp IC6A multiplies this signal with gain +2V/V, op-amp converts result current that passes through device under test (DUT). This current ranges from ±40µA ±40mA, according
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resistor value selected RSENSE. combination selected range, maximum current available equals (approximately) IC6A output (±4.096V max) divided RSENSE. Current through produces bipolar voltage that sensed differential amplifier IC6B. avoid variable-offset error that would otherwise occur with change switch position, this amplifier's inverting-input signal taken from low-impedance, noninverting input rather than inverting input. penalty this choice fixed input-offset error IC7. differential amplifier's gain plus offset supplied result maximum output swing 4.096V) compatible with unipolar input range 12-bit analog-to-digital converter (ADC), IC3. IC3's 3.3k input resistor limits input current event applied overvoltage. requires ±15V supply rails provide sufficient compliance voltage current-source function. supply other ICs, regulate these rails ±5V. During operation, software drives produce current ramp, measures resulting voltage across DUT. This voltage waveform displayed monitor 640x480 resolution, shown examples (Figure Twelve-bit converter resolution excessive with respect this display resolution, bits provides margin higher-resolution monitors examining response with software "zoom."
Figure Examples output from Figure circuit include Schottky diode more complex analog (b). Curve Tracer similar version this article appeared December 1997 issue Electronic Engineering magazine. Revision: July 2001 MORE INFORMATION MAX189: QuickView MAX478: QuickView MAX492: QuickView MAX531: QuickView MAX663: QuickView MAX664: QuickView
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Application Note 253: 2001 Printer Port Controls Curve Tracer

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