PB Fortich

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  • LCD 3- 1 ⁄ 2 Digit A/D Converters

  • Created: Aug 22, 2016

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Summary

In the midst of industrial development, several digital panels bring convenience to the operators. It provides real-time status of the equipment or any system that requires LCD for monitoring. The ICL7106 monolithic Analog-to-Digital Converter (ADC) directly drives no multiplexed Liquid Crystal Display (LCD). It has high input impedances and requires no external display drive circuitry. It has high-impedance CMOS differential inputs, and clock and reference on-chip. It is low noise without hysteresis or overrange hangover.


The analog input is received by series RC circuit that serves as filter. It blocks certain frequencies and passing others that matches the requirement of ICL7106 monolithic ADC IC. The IN HI and IN LO pins are used to have a phase of measurement cycle in the analog section. Below those two pins are the measurement cycle pins, the A-Z, INT, and BUFF. The Auto-Zero (A-Z) phase occurs three events. First, the inputs, IN-HI shorted to analog common. Second, the reference capacitor is charged to the reference voltage, and lastly a feedback loop is closed around the system to charge the auto-zero capacitor C to compensate for offset voltage in the comparator, buffer amplifier and integrator. The Signal Integrate (INT) phase, the internal input high (IN-HI) and input low (IN-LO) are connected to the external pins, the internal short is removed and the auto-zero loop is opened. The converter then integrates the differential voltage between IN-HI and IN-LO for a fixed time. The reference De-Integrate (DI) phase, IN-HI is connected across the previously charge reference capacitor and IN-LO is internally connected to analog common. The Zero Integrator (ZI) phase, input low is shorted to analog COMMON and the reference capacitor is charged to the reference voltage. Note that the reference voltage is 100.0mV, and the full-scale input is 200.0mV. Also, few of the components has different functions, the auto-zero capacitor C2 influence the noise of the system. The reference capacitor C4 is 0.1uF capacitor, which is acceptable, however, a large value is needed to prevent rollover error where a large common-mode voltage exists. The integrating capacitor C3 is 0.22uF in which it ensures that the integrator will not saturate. The integrating resistor R1 is large enough to maintain the amplifiers in the linear region over the entire input voltage range. The oscillator components requires 100kΩ resistor that is recommended for all ranges of frequency. The segment driver pins are provided in which it drives four 7-segments.


This design is applicable in industrial equipment like digital display for monitoring. There are also applications that involve measurement and display of analog data. It can be developed for more advance application.

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