Analysis And Improvement On Non-ideal Factors Of Switched Current

With the continuous development of science and technology, for the integrated circuit design, it is the inevitable trend to achieve the monolithic hybrid simulation and digital integrated circuit. As most of the modern hybrid integrated circuits use the digital circuits, and only few use the analog circuit, so the digital CMOS process is bound to be used for the design process. However, the switched capacitor circuit can not be fully compatible with the digital CMOS process, which limits the integrated circuit development severely, and the switched current technology is proposed for the occasion.Switched current technology, a new and digital analog sampled data processing technology, was proposed by Hughes in1989. Compared with the switched capacitor circuit, as a current basin analog sampled data system, the switched current circuit has the following significant advantages:fully compatible with the digital CMOS process; needing no high-performance linear capacitors and operational amplifiers; having high frequency, low voltage, low power consumption and large dynamic range. So far, the switching current circuit has developed into one of the important and crucial technologies to achieve the integrated circuit with low voltage, low power consumption and large scale, attracting great attention of many scholars at home and abroad.The development background and current situation of the switched current circuit are described in this paper firstly, as well as the basic memory cells and modules of the high-performance switched current. And then, the non-ideal factors are analyzed, which are caused by MOS transistors used as switches and memotrons in the switched current circuit. These non-ideal factors make the switched current circuit’s practical work performance deviate from its ideal performance, make the switched current circuit not be comparable with the switched capacitor circuit, and influence the practical process of the switched current technology seriously. Therefore, how to reduce the non-ideal factors’effects and improve various errors in the circuit has become an important research topic, which is also the research emphasis of this paper.Various errors of the switched-current circuit are described in detail in this paper: the mismatch error, the conductance ratio error, the adjustment error, the charge injection error and the noise error; The two main errors influencing the switched current circuit performance-the charge injection error and the conductance ratio error, are given the corresponding formulas and analyzed in detail. For these two errors, on the basis of the negative feedback technology and the fully differential circuit, according to the idea that the charge injection error can be improved if inversion layer can be eliminated before the switched transistor turns off, a new switched current memory cell with low error is proposed, and HSPICE simulation is carried out. Simulation results show that the new switched current memory cell’s accuracy is basically the same with that of the CVS switched current memory cell. However, compared to CVS circuit and the clock feed-through compensation circuit, the new switched current memory cell has a simple structure and has no complex clock control.