Sub-threshold R-MOSFET tunable resistor technique

An R-MOSFET resistor structure that enables extension of the MOSFETs' operation into sub-threshold region while preserving good linearity performance is presented. The technique essentially relies upon a linear current division between two nonlinear branches each comprising a linear resistor and a MOSFET operating at sub-threshold inversion. The feasibility of the sub-threshold R-MOSFET structure is demonstrated via breadboard experiment using array transistors, and via simulation using a 0.18 mum CMOS process     

High frequency current mode oscillator employing fTintegration technique

A low distortion high frequency oscillator is described, which is a development of the recently proposed f_T-integrator, in which an amplitude control circuit is embedded inside the integrator. Simulation results suggest that, for the oscillation range 1-2.6 GHz, the total harmonic distortion (THD) of the output current signal is well below 0.5% for the output current level at 50% modulation depth (peak-to-peak). The phase noise of the oscillator is simulated to be -72 dBc/Hz at 1 MHz offset for 1% THD output current     

Selection of the common-mode feedback network connection of fully differential Gm-C filters

It is well known that fully differential (FD) structures have many advantages over their single-ended counterparts. However, the main disadvantage of FD circuit is the potential instability caused by the inherent common-mode (CM) positive feedback loop. To solve such an instability problem, extra common-mode feedback (CMFB) and/or common-mode feedforward (CMFF) circuitries are often incorporated to stabilise the circuits. We present a systematic method for checking the stability condition and identifying the most suitable CMFB network connection for a particular FD Gm-C filter. It has been demonstrated that the CMFB network connection that provides highest CM rejection is not necessarily the conventional arrangement commonly used in FD Gm-C design.     

Ladder-simulation elliptic bandpass active-RC filter structure employing identical resistors

A novel structure of the ladder-based elliptic bandpass active-RC filter is presented. Unlike the previously reported elliptic bandpass active-RC filter, the proposed filter contains resistors with identical value and is therefore more suitable for integrated-circuit realisation. Also, according to the simulation results, the proposed elliptic bandpass filter performs better than the reciprocator-based active-RC filter, which employs identical resistors, in terms of noise, power and area. Additionally, the proposed filter structure was also found to be less sensitive than both of the aforementioned structures.