Design of 10-Bit Dual Slope ADC for ISFET based pH Meter

Abstract

In this thesis work, a 10-bit Dual slope ADC for ISFET based pH sensor has been designed which consumes low power and have high resolution. This is implemented and simulated with Cadence tool in UMC 0.18μm technology with a 3.3V power supply. Different types of ADC are given in literature and they are used according to the intended application. In the biomedical field, accuracy is main concern so dual slope ADC is a best choice. Dual slope ADC is very popular due to its simplicity and higher accuracy. In this ADC there is no need of any DAC which reduces the cost of ADC. In ISFET based pH meter, a discrete value is available to the input of ADC corresponding to the pH solution so there is no requirement of any sample and hold circuitry. This ADC has three main components: Integrator, comparator and control logic. In the ISFET based pH meter input to the integrator comes from the temperature compensation circuitry, which has upper range output so for an integrator design, an N-channel input two stage operational amplifier is taken in use because an n channel-input two stage operational amplifier have ICMR near to power supply and provide high gain. To achieve the high resolution, a cascaded comparator has been designed which enhance the resolution while keeping the ability of low power consumption. For controlling the whole operation of ADC, Melay state machine based control logic has been designed. To display the digital output of ADC on LCD, a 3 ½ LCD display driver circuitry has been designed. This LCD display, shows the value of pH from 2 to 12. Layouts of all the components have been designed and post layout simulation and process corner simulation has done successfully.