The development of bipolar log-domain filters in a standard CMOS process /

Log-domain filters have emerged in recent years as a new and important class of continuous-time filter. The attractive features of these filters include their compact structure, their potential to run at high frequencies while operating from low power supplies, and their electronic tunability. At the heart of the log-domain filtering technique is the logarithmic/exponential relationship between voltage and current in a transistor. In this work, the development of log-domain filters in CMOS technology will be investigated. The lateral bipolar transistor, inherent to CMOS processes, will be used for this purpose.A SPICE compatible model for a lateral PNP transistor, fabricated in 0.35mu CMOS technology, is presented. A log-domain integrator, which makes use of both lateral PNP transistors and MOSFET transistors operating in strong inversion, as well as a biquadratic low-pass log-domain filter and a third order elliptic low-pass log-domain filter, have each been designed and characterized in 0.35mu CMOS technology. Experimental results indicate that these filters are capable of operation at frequencies up to 10 MHz. For the elliptic filter operating at a bias current of 10 muA, the experimentally measured total harmonic distortion is -39.6 dB for an input current of 5 muA (a 50% current modulation index), the dynamic range is -34.1 dB, and the total power consumption is 183 muW/pole from a 2.5 V supply. These filters are capable of operating at significantly higher frequencies than CMOS log-domain filters described in the literature which make use of MOSFET transistors operating in weak inversion