BIAS VOLTAGE GENERATOR FOR THE VOLTAGE-RESPONSIVE TUNING ELEMENTS IN AN ELECTRONICALLY TUNED RADIO RECEIVER

• US 3,758,865 A
• Filed: 01/18/1972
• Issued: 09/11/1973
• Est. Priority Date: 01/18/1972
• Status: Expired due to Term

• Current Assignee: James L. Mckibben
• Original Assignee: James L. Mckibben
• Inventors: McKibben, James L.
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Ellis, William T.
• Application Number:
  US05/218,788
• Time in Patent Office: 602 Days
• Field of Search: 325/416,417,418,465,464,419,420,421,422,423,453 334/14 331/1A,1R,17,30,36,40,41,34,177R
• US Class Current: 455/195.1
• CPC Class Codes: H03J 3/185 with varactors, i.e. voltage variable reactive diodes

Abstract

A circuit for tuning an electronically tuned radio receiver in which the tuning voltage for tuning the radio receiver is supplied to the positive input of a first differential amplifier having a high gain whose output is connected across a voltage responsive capacitive element for controlling the frequency of oscillation of a voltage controlled local oscillator. The output of this voltage controlled local oscillator is supplied to a linear frequency-to-voltage converter whose output is supplied to the negative input of the first differential amplifier to maintain the output of the local oscillator a linear function of the tuning voltage. The tuning voltage is also supplied to the positive input of a second differential amplifier whose output is supplied to the positive input of a third differential amplifier having a high gain. The output of this amplifier is connected across a voltage responsive capacitive element in a reference voltage controlled oscillator to control the frequency of oscillation thereof and across respective voltage responsive capacitive elements in the antenna and RF tuned circuits to control the tuned frequency thereof. The output of the reference voltage controlled oscillator is supplied to a linear frequencyto-voltage converter whose output is connected to the negative input of the third differential amplifier to maintain the frequency at which the reference voltage controlled oscillator, antenna and RF tuned circuits are tuned a linear function of the input voltage to the positive input of the third differential amplifier. A constant DC voltage is supplied to the negative input of the second differential amplifier to effect the tracking of the antenna and RF tuned circuits to the output of the voltage controlled local oscillator at a constant difference frequency equal to the IF frequency.

Claims

1. A superheterodyne radio receiver having an intermediate frequency f1, comprising, means for generating a tuning voltage having a magnitude Vt;

first differential amplifier means having a voltage-to-voltage gain G1 for subtracting the magnitude of a signal supplied to a first terminal thereof from the magnitude of a signal supplied to a second terminal thereof and generating a first bias voltage having a magnitude B1 equal to the difference times G1;

means for coupling the tuning voltage having the magnitude Vt to the second terminal of the first differential amplifier means;

a voltage tuned local oscillator coupled to the output of the first differential amplifier means and having a nonlinear transfer function A1 for developing a local signal having a frequency f1 equal to A1B1;

a first frequency-to-voltage converter coupled to the output of the voltage tuned local oscillator and having a linear transfer function H for developing a first feedback signal having a magnitude F1 equal to Hf1;

means for coupling the first feedback signal to the first terminal of the first differential amplifier means, said functions A1, G1 and H having a product much greater than unity whereby f1 substantially equals Vt/H ;

second differential amplifier means having a voltage-to-voltage gain G2 for subtracting the magnitude of a signal supplied to a first terminal thereof from the magnitude of a signal supplied to a second terminal thereof and generating a second bias voltage having a magnitude B2 equal to the difference times G2;

a voltage tuned reference oscillator coupled to the second differential amplifier means and having a nonlinear transfer function A2 for developing a reference signal having a frequency f2 equal to A2B2;

a second frequency-tovoltage converter coupled to the output of the voltage tuned reference oscillator and having the linear transfer function H for developing a second feedback signal having a magnitude F2 equal to Hf2;

means for coupling the second feedback signal to the first terminal of the second differential amplifier means;

means coupled to the means for generating a tuning voltage for generating a reference tuning voltage having a magnitude VR spaced from the tuning voltage having the magnitude Vt by a constant having a magnitude VI equal to HfI;

means for coupling the reference tuning voltage having the magnitude VR to the second terminal of the second differential amplifier means;

said functions A2, G2 and H having a product much greater than unity whereby f2 substantially equals VR/H ; and

a voltage responsive tuned circuit coupled to the output of the second differential amplifier means and having the nonlinear transfer function A2 for tuning the radio receiver to the frequency f2;

whereby the radio receiver is tuned to a frequency f2 which is spaced from the frequency f1 of the output signal of the voltage tuned local oscillator by the frequency fI and the tuned frequency f2 is linearly related to the magnitude Vt of the tuning voltage.

2. In an electronically tunable radio receiver having antenna, RF and local oscillator circuits, each circuit including a tuned circuit having a voltage responsive reactive element responsive to a bias voltage applied thereacross for tuning the radio receiver over its frequency band, the local oscillator having a nonlinear voltage-to-frequency transfer function A1 and the antenna and RF circuits each having a nonlinear voltage-to-frequency transfer function A2, a circuit for biasing each of the voltage responsive reactive elements comprising, in combination, a tuning voltage generator for generating a tuning voltage at an output thereof to effect tuning of the radio receiver;

a first differential amplifier having first and second inputs and a gain G1 for subtracting a voltage at its second input from a voltage at its first input and generating an output voltage signal equal to the difference times the gain G1;

means for applying the output voltage signal of the first differential amplifier across the voltage responsive reactive element in the tuned circuit of the local oscillator, the local oscillator having a frequency of oscillation determined by the amplitude of said signal;

a first frequency-to-voltage converter having a linear transfer function H connected to the output of the local oscillator and the second input of the first differential amplifier for supplying to the second terminal of the first differential amplifier a voltage having a magnitude linearly related to the frequency of oscillation of the local oscillator, the product of the functions A1, G1 and H being much greater than unity;

means connecting the output of the tuning voltage generator to the first input of the first differential amplifier;

a second differential Amplifier having first and second inputs, said amplifier being effective to subtract a voltage at its second input from a voltage at its first input and generating an output voltage signal equal to the difference;

means connecting the output of the tuning voltage generator to the first input of the second differential amplifier;

a reference oscillator having the nonlinear voltage-to-frequency transfer function A2 and having a tuned circuit including a voltage responsive reactive element responsive to a bias voltage applied thereacross for tuning the reference oscillator;

a third differential amplifier having a gain G2 and having a first input connected to the output of the second differential amplifier and a second input for subtracting a voltage at its second input from a voltage at its first input and generating an output signal equal to the difference times the gain G2;

means for applying the output voltage signal of the third differential amplifier across the voltage responsive reactive element in the tuned circuit of the reference oscillator, the reference oscillator having a frequency of oscillation determined by the amplitude of said signal;

a second frequency-to-voltage converter having the linear transfer function H connected to the output of the reference oscillator and to the second input of the third differential amplifier for supplying to the second terminal of the third differential amplifier a voltage having a magnitude linearly related to the frequency of oscillation of the reference oscillator, the product of A2, G2 and H being much greater than unity;

means applying the output voltage of the third differential amplifier across the voltage responsive reactive elements in the antenna and RF tuned circuits, the antenna and RF tuned circuits being tuned to a frequency determined by the amplitude of said signal;

means for supplying a bias signal to the second input of the second differential amplifier to cause the antenna and RF tuned circuits to be tuned to a frequency different from the frequency of the output signal of the local oscillator by an amount equal to a desired IF frequency, the magnitude of the bias signal being equal to H times the IF frequency, whereby the antenna, RF and local oscillator tuned circuits are in track throughout the frequency band of the radio receiver and the tuned frequency of the radio receiver is a linear function of the tuning voltage at the output of the tuning voltage generator.