Design and Analysis of Highly Linear Integrated Wideband Amplifiers

This dissertation deals with techniques for designing integrated amplifiers with high linearity. Amplifiers with operating frequencies from Audio to RF have been built. An enhanced feedback configuration, capable of very low distortion, is presented. Also presented is a statistical method for relating the distortion of a wideband signal to the total harmonic distortion (THD) of a single tone. Two fully integrated class AB CMOS audio power amplifiers that are capable of driving 8Ohm loudspeaker loads directly from the chip are presented. Two different topologies are used, both resulting in low distortion and high output voltage swing. The second amplifier operates with supply voltages down to 1.5V. Both amplifiers feature advanced phase compensation strategies to be able to drive loudspeakers with up to 100nF and down to 8Ohm without external components, such as load stabilising networks. Two wideband IF amplifiers are presented. They are fully integrated and have high linearity from DC to 20MHz. Both have differential inputs and outputs. To achieve high linearity, large feedback together with double nested Miller compensation are used, resulting in a high degree of linearisation of the output stage. One of the amplifiers is built in CMOS and the other is built using npn-only bipolar technology. One fully integrated RF power amplifier in 0.8um CMOS without coils is presented. The purpose of this amplifier is to investigate how fast and linear a power amplifier can be made in CMOS, without using coils to resonate with major parasitic capacitances. This investigation is done in order to be able to build fast RF power amplifiers without coils when the speed of the CMOS processes increases in the future. An enhanced feedback scheme, which is the subject to a patent application, is also presented. By connecting a negative impedance to the inverting input of a feedback amplifier, the feedback can be boosted to become infinite at a certain frequency. Thereby the distortion at this frequency can be eliminated completely. The gain of the arrangement is equal to that with an ideal amplifier. Finally a novel method of how to relate the intermodulation distortion of a wideband signal to the total harmonic distortion (THD) of a single tone test is presented. The motivation for this is that the THD, as opposed to the intermodulation distortion of the wideband signal, is easy to measure and use as a design parameter. It is shown how to select both the amplitude and the frequency of the single tone to get the same distortion power as with a wideband signal. (Less)