Design Of Second Order∑-ΔDAC

DAC, referred DAC,it is a device which converts digital into analog signal. Thetypical D/A converter is basically consists of four section, resistor network, operationalamplifier, reference power supply and analog switches. As mainly relying on the analoguedevice, it is difficult to achieve high resolution. Σ-ΔDAC is a kind of D/A converter basedon the digital signal processing technology.As low accuracy requirements of analogdevices, less demanding of device matching degrees and the process of easy to implement,so it can achieve high resolution and stability. it may have a good prospect.As ahigh-precision signal converter, Σ-Δ DAC has a wide range of applications,in digital audio,communications and other fields.I design a new circuit by analyzing the circuit of chip AD421based on domesticproduction line. The paper introduced the principle of the digital-to-analog converter, andanalyzed the circuit in accordance with the layout photos. The circuit comprises anoscillator, a input shift register, a latch, a16/17mode conversion module, a Σ-Δ modulatormodule, a filter circuit and other functional modules. The theoretical analysis andsimulation verification proved the correctness of the extracted circuit. The circuit wasredesigned based on the HHNEC BCD035process and all design process has been completed.The main work of the paper is to accomplish the layout design of the circuit with cadencesoftware based on the0.35μm design rule and passed DRC and LVS. The anticipativeobjective is attained in the design. Because of the craft is more advanced, the chip area isreduced in the layout, and the product cost was also reduced.Simulation results show that, the range of output current is2uA~10uA in the16-bitmode and the output current range is1.75uA to12uA in17-bit mode. The resolution is0.001uA and setup time is8ms.