Solid state VHF frequency converter

This paper describes the design of a transistor frequency converter suitable for use in mobile communication receiver equipment. Two-port network theory is used to design a 250-Mc RF amplifier, a 250- to 60-Mc mixer, a 310-Mc local oscillator and a two-stage 60-Mc IF amplifier. Performance of silicon planar transistors are first predicted from calculations based on y parameters of these transistors and then compared with experimentally determined performance. The mathematical techniques used in the design of this circuitry are discussed in some detail. Basic design philosophy using terminal, rather than internal, parameters is introduced. Power gain and stability are described in terms of terminal admittance parameters and high frequency performance curves of a popular high frequency silicon transistor are presented. Finally, a transistor frequency converter system suitable for mobile communications equipment is discussed. In particular, the sensitivity, noise figure, selectivity and stability are developed. The over-all converter performance values are: Conversion Gain ................65 db Bandwidth ...................... 4 Mc Noise Figure ................... 6 db Image Rejection ................25 db Temperature sensitivity data indicated that the local oscillator was most sensitive to temperature change and caused the over-all gain to vary from 62.5 db @ 5°C to 65 db at 25°C to 60 db @ 50°C. Center frequency changes (in the same order) were 57 Mc, 60 Mc and 65 Mc.