Design Of High Resolution∑△Analog To Digital Converter

Among all kinds of Analog-to-Digital Converters (ADCs), Sigma DeltaAnalog-to-Digital Converter (ΣΔADC) is widely used in audio and sensor circuits forits low speed, low power and high resolution. Based on comparison and analysis ofseveral different types of ADC on structure and working principle, ΣΔADC is chosento fulfill the requirement of the sensor. A ΣΔADC is mainly made up of a ΣΔmodulator and a decimation filter. The thesis is focused on the most important anddifficult part——the ΣΔ modulator design. After performing behavioral topologysimulation, a single-loop one-bit third-order full-differential ΣΔmodulator is developedand implemented in a standard0.18-μm CMOS technology. Operating from a1.8Vsupply, it achieves a dynamic range of95dB with power consumption less than1mWat a20-KHz bandwidth. It occupies an active area of0.36mm2.The main work are as follows:1. Model the structure of the modulator and determine coefficients of the topologyconsidering several circuit compenent non-idealities. Non-idealities such asthermal and flicker noise, dc offset, finite open-loop voltage gain, limitedbandwidth, finite slew-rate and jitter are taken into account and modeled intopology simulation to select a proper structre, which limit the effects of thenon-linearities in an acceptable range and determine the coefficients.2. Design a high linearity modulator. As the linearity of the modulator is mostlyaffected by the quantizer, a one-bit quantizer made up of a dynamic comparator anda SR latch is chosen.The main advantages of the design are its enhanced speed(或reduced hysteresis) and the completely dynamic operation showing no static powerconsumption.3. Design a low power, high gain operational transconductance opamp. Asnoise-shaping is influenced by opamp gain, a current-starving gain enhancementfor higher dc gain and switch-capacitor CMFB for larger output swing and minorpower are taken.4. Design circuits and layout of the modulator. Linear switch and bandgap areemployed to ensure the linearity and precision. Meanwhile, appropriate circuitlayout and wiring, as well as guard ring are adopted to improve matching andminize the noise.