Cascode FM tuner for a radio receiver
First Claim
1. In a tuner for converting radio frequency signals to a fixed intermediate frequency and designed for automatic frequency control, the combination comprising:
- (1) a first source of variable potentials for effecting automatic frequency control,(2) a mixer including;
(a) a first transistor having base, emitter and collector electrodes,(b) an input circuit for said mixer comprising an r.f. transformer having a first winding tuned to resonance and coupled to a source of r.f. signals; and
an untuned, secondary winding connected to said base electrode for coupling signals thereto, and connecting said base electrode to said first source in a path of low d.c. impedance,(c) a mixer output circuit connected to said collector electrode and tuned to said fixed intermediate frequency for deriving signals at the intermediate frequency,(3) an oscillator comprising;
(a) a second transistor connected in circuit with said first transistor having base, emitter and collector electrodes,(b) a bypass capacitor for grounding the base of said second transistor at the oscillator frequency,(c) a second source of d.c. potentials connected between the base electrode of said second transistor and ground,(d) a tuned resonant circuit for said oscillator providing a single path of low d.c. impedance between the emitter of said first transistor and the collector of said second transistor to equalize the currents between said transistors to transfer the voltage variations in said first source less the voltage drop in the input junction of said first transistor to the collector of said second transistor, and to provide oscillator injection into said mixer, and(e) a resistance connected between the emitter of said second transistor and ground for setting the desire current levels in both said transistors.
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Accused Products
Abstract
An FM tuner having an improved automatic frequency control circuit and designed for use in an AM-FM receiver is described. The tuner employs a mixer transistor and an oscillator transistor connected in circuit so that they form a single series path across the bias source. This feature permits one to control conduction in both transistors by control of one and thus simplifies both biasing and mode conversion. Preferably, the transistor bias source and the source of AFC control potential are consolidated to save decoupling components. When the base of the mixer transistor is connected to the source through a low d.c. impedance, the AFC potential is transferred (less the mixer junction drop) to the collector of the oscillator transistor, where it provides sensitive automatic frequency control action. The circuit design uses a minimum of components.
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Citations
9 Claims
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1. In a tuner for converting radio frequency signals to a fixed intermediate frequency and designed for automatic frequency control, the combination comprising:
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(1) a first source of variable potentials for effecting automatic frequency control, (2) a mixer including; (a) a first transistor having base, emitter and collector electrodes, (b) an input circuit for said mixer comprising an r.f. transformer having a first winding tuned to resonance and coupled to a source of r.f. signals; and
an untuned, secondary winding connected to said base electrode for coupling signals thereto, and connecting said base electrode to said first source in a path of low d.c. impedance,(c) a mixer output circuit connected to said collector electrode and tuned to said fixed intermediate frequency for deriving signals at the intermediate frequency, (3) an oscillator comprising; (a) a second transistor connected in circuit with said first transistor having base, emitter and collector electrodes, (b) a bypass capacitor for grounding the base of said second transistor at the oscillator frequency, (c) a second source of d.c. potentials connected between the base electrode of said second transistor and ground, (d) a tuned resonant circuit for said oscillator providing a single path of low d.c. impedance between the emitter of said first transistor and the collector of said second transistor to equalize the currents between said transistors to transfer the voltage variations in said first source less the voltage drop in the input junction of said first transistor to the collector of said second transistor, and to provide oscillator injection into said mixer, and (e) a resistance connected between the emitter of said second transistor and ground for setting the desire current levels in both said transistors. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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Specification