A novel and low-cost white noise generator using an ordinary Zener diode as the source of noise is presented. The Zener diode is driven by a stable dc current source such that the noise signal power ...generated by the Zener diode increases with increasing frequency under right dc current biasing. A 6-stage MMIC amplifier block was designed to increase the noise power further. Since the gain-frequency response of the amplifier block has a negative slope as the frequency increases, the positive slope of the noise power produced by the Zener diode is balanced with the negative slope of the amplifier gain. The resulting amplified noise signal appears to have almost constant power at the output of the amplifier. As a result, the designed noise generator exhibits white noise characteristics, and is used as a tracking generator to measure insertion loss of a RF/microwave filter.
A simple analogue technique called auxiliary envelope tracking, or AET, is presented, which is shown to be capable of improving the efficiency of a radio frequency power amplifier (RFPA). This AET ...signal is an amplified envelope signal that supplies the drain port of the RFPA. The concept of AET is explained and a theoretical background for the technique is presented. The main feature of this technique lies in the separation of the DC and AC components of the tracking signal. This allows for a very simple and low-cost tracking generator design that consists of a simple source follower amplifier and an RF broadband transformer. A practical system has been implemented and the measured results are obtained for WCDMA signals. A measurement on the realised system shows a 50% improvement in the drain efficiency at average output power of 33 dBm of a 25 W GaN. This substantial improvement is achieved at a competitive WCDMA signal with peak-to-average envelope power ratio of 9.17 dB.
A tracking generator of calibrated harmonics has been tested at the Istituto Elettrotecnico Nazionale Galileo Ferraris. This system acquires the sinusoidal input supplied by a precision ac ...calibrator, and the internal DSP produces, by means of a digital-to-analog converter (DAC), an output signal combination of calibrated harmonics components, which is added to the sinusoidal signal of the calibrator. In this way, an ordinary 12-bit DAC can produce a precision signal with an assigned THD less than 10%. Some algorithms for generating the signal and for tracking with high accuracy the internal reference to the external input signal have been developed, which allow the frequency and phase difference to be recovered within 10/sup -4/ rad in less than 0.1 s.
