Design and modelling of a voltage controlled N-well resistor using the MOS tunneling diode structure

In standard CMOS technologies, only N-well or polysilicon resistors are available. The main drawback of these resistors is that their value is not perfectly controlled due to process dispersion. Furthermore, their absolute value is relatively low. Then, when large resistances are needed, the only issue is to implement very long resistors which require large silicon area. In this paper, a new N-well resistor using the MOS tunneling diode structure is presented. This particular structure, which is compatible with any CMOS process, gives the opportunity to increase and to tune the device resistance. As a consequence, this device can be seen as a voltage controlled resistor (VCR). With a CMOS 0.6 μm technology, ±10% tuning range and/or up to 20% silicon area saving has been reached. A continuous and smooth compact model for the VCR is also presented. This model can be easily implemented in a high-level analog description language such as VHDL-AMS.