Digital Isolator Analysis And Design Based On On-chip Transformer

Due to the rapid development of science and technology, electrical equipment is applied into every aspect of people’s life, and electrical safety impacts everyone. Isolation circuit is the most commonly means of protection. The main reason of isolation is protecting us from dangerous voltage and current damage. Usually we will adopt isolation in these two cases: possible harm to personnel or equipment from potential electrical surge; there must be avoided interconnection of different position and the division of the ground loop. Isolation circuit avoids the current conduction and at the same time allows data or power transmission between two points.Isolator can be divided into three categories in principle: general optoelectronic isolator, inductance isolator and capacitor isolator. Traditional isolator designed by discrete component, especially optoelectronic isolator(OC), not only has large volume, high power consumption, but also low communication transmission rate. It cannot satisfy application of low power consumption, high speed and miniaturization. Therefore, this paper puts forward a kind of monolithic integrated digital isolator scheme based on the on-chip transformer.On-chip transformer is made on the silicon wafer using MEMS technology, and it has two mutual coupling inductance coils, 20 um distance. Compared with discrete transformer, its performance for high frequency signal coupling is better, and at the same time it has no magnetic saturation or demagnetization time.For on-chip transformer, we encode the digital signal into high speed pulse. Two pulses representative the rising edge, and one pulse for the falling edge. Such a high frequency pulse stream has good coupling between the inductors. On the other side we receive the pulse stream and decode signal in accordance with the corresponding rules. When there is no input, refresh circuit periodically gives refresh pulses to achieve DC signal transmission creatively. This is very important for some cases like a clear power-on state, low data rate of input waveform, a constant dc input. The isolator based on on-chip transformer has obvious advantages over traditional isolators in all aspects of power consumption, size, transmission rate, so it has broad application prospects.In this paper, our research subject is digital isolator based on the on-chip transformer. We first describe the development process of isolation and characteristics of various isolators, on-chip transformer MEMS production process. Then we focus on analysis and simulation of the chip encoding and decoding circuit and chip application, finally review the main work and features of this subject.