Features of Developing Silicon-Germanium Frequency Converters, Including an Integrated PLL Synthesizer
Modified circuits of Gilbert mixer are basic elements in the vast majority of frequency converters . A fairly large number of works [3, 4, 5] is known today, which investigate the properties of this circuit and propose improvements of dynamical and frequency characteristics. But in engineering practice, depending on fabrication technique, the issue of active mixer circuit optimization is a major one.
This paper presents the results of the following devices development: double balanced mixer with L-band, frequency converter with С-band, VLSI of fractional frequency synthesizer with embedded VCO and two balanced mixers.
Double balanced mixer with L-band has the following features:
• built by modified Gilbert mixer circuit;
• output is made in the form of “open collector”, which at supply voltage of 3V made it possible to attain value of input compression point +10dBm;
• the presence of digital control for current consumption, which enables attaining noise factor lower than 12dB;
• the presence of sleep and waiting modes of operation.
Frequency converter with С-band has the following characteristics: conversion ratio is 15dB, operating frequencies band of valid signal — from 20МHz to 7GHz, output point of compression +9dBm, noise factor –14dB.
Distinctive feature of mixers, which constitute a part of fractional frequency synthesizer, is their wide dynamical range attained at supply voltage of 3V. Modified Gilbert circuit constitutes a mixer base, where input converter voltage-current is linearized by means of structured method , enabling one to provide the effect of partial noise compensation . As a result, the mixer has a value of input compression point +10dBm, noise factor being lower than 11dB. Total microcircuit current consumption does not exceed 170mA. Phase noises of heterodyne at 1GHZ and tune-out from carrier at 10kHz do not exceed –95dB/Hz.
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