Ari Vilander

Cancellation of second-order intermodulation distortion and enhancement of IIP2 in common-source and common-emitter RF transconductors

In this paper, a biasing technique for cancelling second-order intermodulation (IM2) distortion and enhancing second-order intercept point (IIP2) in common-source and common-emitter RF transconductors is presented. The proposed circuit can be utilized as an RF input transconductor in double-balanced downconversion mixers. By applying the presented technique, the achievable IIP2 of the mixer is limited by the linearity of the switching devices, component mismatches, and offsets. The proposed circuit has properties similar to the conventional differential pair transconductor in that it ideally displays no IM2 distortion. However, the presented circuit is more suitable for operation at low supply voltages because it has only one device stacked between the transconductor input and output. In the conventional differential pair, two devices consume the voltage headroom. The noise performance of the proposed transconductor is similar to the noise performance of the traditional common-source (emitter) and differential pair transconductors at given bias and device dimensions. On the other hand, the third-order intercept point (IIP3) of the presented transconductor is slightly higher than the IIP3 of the differential pair transconductor at given bias. Finally, the proposed circuit can also be employed as a current mirror, the ratio of which is very insensitive to the voltage swings at the gate or base of the current mirrored transistor.

A gain stabilization technique for tuned RF low-noise amplifiers

A gain stabilization technique for tuned integrated low-noise amplifiers (LNAs) is presented. The proposed method regulates the LC-tuned load impedance of the amplifier at the operation frequency against variations of passive devices in integrated circuit (IC) process. The impedance stabilization technique is based on the excellent relative accuracy of integrated resistors. Although the absolute deviation of the integrated resistors can be as large as /spl plusmn/20%, the relative deviation can be made smaller than /spl plusmn/1% provided that resistors are placed close to each other. By applying the proposed method, the voltage-gain variation of the inductively degenerated common-source LNA, which is the most popular LNA architecture, can be reduced several decibels. As a consequence, the entire radio receiver can more easily meet its specifications in the presence of IC process variations and the product yield is improved. Finally, besides the LNAs, the presented stabilization technique can also be utilized in other tuned amplifiers, filters or oscillators employing damped LC-tuned loads.