Enrique Ferrer

IIP3 estimation from the gain compression curve

Classical analysis of transistor amplifier performance shows 9.6 dB as the difference between the input-referred third-order intercept point (IIP3) and 1-dB gain compression point. An analysis of amplifier gain compression shows that this is not the case, that at least fifth-order harmonics play a role in the gain compression curve and that the classical analysis is incorrect for submicrometer RF transistor amplifiers. Another approach is presented that estimates the values of IIP3 from a single-tone RF power gain data. This approach is successfully applied to simulations of a common-source amplifier and a differential amplifier with resistive load. Measurements of commercial amplifiers show that IIP3 can be estimated from their gain compression curves. This modeling approach of determining IIP3 from gain compression curves can simplify test protocol, shorten test time, and lower cost of integrated-circuit production test.

Limit-cycle oscillations in a log-domain-based filter

A circuit is presented for a class-AB fully differential log-domain parallel resonator based on a capacitively loaded gyrator. It is shown that if floating rather than shunt capacitive loads are used, the circuit is stable for small stimuli, but can be triggered into steady-state limit-cycle oscillations by large enough transient inputs. The nature of the instability is explored and it is shown how SPICE transient analysis can be used to detect the instability and locate the separatrix between stable-equilibrium-point-seeking and limit-cycle-seeking regions of state space. Analysis is also presented to demonstrate that the circuit with floating capacitors does not implement an externally linear transfer function, and therefore, it is not a true log-domain circuit.