Amplifying circuit with power supply switching circuit

• US 5,834,977 A
• Filed: 10/30/1996
• Issued: 11/10/1998
• Est. Priority Date: 10/31/1995
• Status: Expired due to Term

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Inventors: Sugimoto, Satoshi, Maehara, Eiju
• Primary Examiner(s): Mullins, James B.
• Application Number:
  US08/740,759
• Time in Patent Office: 741 Days
• Field of Search: 330/202, 330/267, 330/273, 330/297
• US Class Current: 330/297
• CPC Class Codes: H03F 1/0238 using supply converters

Abstract

An amplifying circuit according to the present invention has an amplifying unit for amplifying an input signal to produce an amplified signal, a battery for generating a constant voltage (a first voltage), a step-up converter for always generating an increased voltage (or a second voltage) by increasing the constant voltage, and a selection changing circuit for supplying the increased voltage to the amplifying unit as an electric source voltage when a level of the amplified signal is higher than the constant voltage and supplying the constant voltage to the amplifying unit as the electric source voltage when a level of the amplified signal is lower than the constant voltage. Therefore, because the electric source voltage supplied to the amplifying unit is changed according to the level of the amplified signal, a loss occurring in an electric power consumed in the amplifying unit can be reduced. Also, because the increased voltage is always generated by the step-up converter as compared with a prior art in which any increased voltage is not always generated, even though the increased signal is a high frequency signal, the electric source voltage can reliably change with the level of the amplified signal, so that any distortion of the amplified signal can be prevented.

Claims

1. An amplifying circuit comprising:

an amplifying unit for amplifying an input signal, thus generating an amplified signal;

an electric source for generating a first voltage;

a bypass circuit arranged between the electric source and the amplifying unit for supplying the first voltage generated by the electric source to the amplifying unit;

a voltage increasing circuit arranged in parallel to the bypass circuit for always increasing the first voltage generated by the electric source, thus generating a second voltage; and

a selection changing circuit for supplying the second voltage generated by the voltage increasing circuit to the amplifying unit in cases where a level of the amplified signal output from the amplifying unit is higher than the first voltage generated by the electric source and supplying the first voltage to the amplifying unit in cases where the level of the amplified signal is lower than the first voltage, wherein the amplifying unit includes

a supplementary electric source unit for generating a third voltage changing with the level of the amplified signal from the first voltage generated by the electric source or the second voltage generated by the voltage increasing circuit and supplying the third voltage to the amplifying unit as an electric source voltage for the amplifying unit.

2. An amplifying circuit according to claim 1 in which the selection changing circuit comprises:

a comparator for comparing a reference voltage lower than the first voltage with the level of the amplified signal; and

a switching element arranged between the voltage increasing circuit and the amplifying unit for setting to an "on" condition to supply the second voltage to the amplifying unit in cases where the level of the amplified signal is higher than the reference voltage as a result of the comparison performed by the comparator and setting to an "off" condition to supply the first voltage to the amplifying unit in cases where the level of the amplified signal is lower than the reference voltage as a result of the comparison performed by the comparator.

3. An amplifying circuit comprising:

an amplifying unit for amplifying an input signal, thus generating an amplified signal;

an electric source for generating a first voltage;

a bypass circuit arranged between the electric source and the amplifying unit for supplying the first voltage generated by the electric source to the amplifying unit;

a voltage increasing circuit arranged in parallel to the bypass circuit for always increasing the first voltage generated by the electric source, thus generating a second voltage; and

a selection changing circuit for supplying the second voltage generated by the voltage increasing circuit to the amplifying unit in cases where a level of the amplified signal output from the amplifying unit is higher than the first voltage generated by the electric source and supplying the first voltage to the amplifying unit in cases where the level of the amplified signal is lower than the first voltage, wherein the voltage increasing circuit is a step-up converter having

a switching element for repeating an ON/OFF operation and increasing the first voltage according to a duty ratio of the ON/OFF operation; and

an oscillator for controlling the ON/OFF operation of the switching element.

4. An amplifying circuit according to claim 3 in which the electric source is a battery used for an on-vehicle type system.

5. An amplifying circuit according to claim 3 in which the selection changing circuit comprises:

a comparator for comparing a reference voltage lower than the first voltage with the level of the amplified signal; and

a switching element arranged between the voltage increasing circuit and the amplifying unit for setting to an "on" condition to supply the second voltage to the amplifying unit in cases where the level of the amplified signal is higher than the reference voltage as a result of the comparison performed by the comparator and setting to an "off" condition to supply the first voltage to the amplifying unit in cases where the level of the amplified signal is lower than the reference voltage as a result of the comparison performed by the comparator.

6. An amplifying circuit comprising:

an amplifying unit for amplifying an input signal, thus generating an amplified signal;

an electric source for generating a first voltage;

a bypass circuit arranged between the electric source and the amplifying unit for supplying the first voltage generated by the electric source to the amplifying unit;

a voltage increasing circuit arranged in parallel to the bypass circuit for always increasing the first voltage generated by the electric source, thus generating a second voltage;

a selection changing circuit for supplying the second voltage generated by the voltage increasing circuit to the amplifying unit in cases where a level of the amplified signal output from the amplifying unit is higher than the first voltage generated by the electric source and supplying the first voltage to the amplifying unit in cases where the level of the amplified signal is lower than the first voltage; and

a microcomputer for stopping the operation of the voltage increasing circuit in cases where an AM radio is operated in the neighborhood of the amplifying unit or the voltage increasing circuit, and for controlling signals in the amplifying circuit.

7. An amplifying circuit according to claim 6 in which the voltage increasing circuit comprises:

a switching element for repeating an ON/OFF operation and increasing the first voltage according to a duty ratio of the ON/OFF operation; and

an oscillator for controlling the ON/OFF operation of the switching element, wherein the operation of the oscillator is stopped under the control of the microcomputer in cases where an AM radio operating signal indicating the operation of the AM radio in the neighborhood of the amplifying unit or the voltage increasing circuit is input to the microcomputer.

8. An amplifying circuit according to claim 6 in which the electric source is a battery used for an on-vehicle type system.

9. An amplifying circuit according to claim 6 in which the selection changing circuit comprises:

a comparator for comparing a reference voltage lower than the first voltage with the level of the amplified signal; and

a switching element arranged between the voltage increasing circuit and the amplifying unit for setting to an "on" condition to supply the second voltage to the amplifying unit in cases where the level of the amplified signal is higher than the reference voltage as a result of the comparison performed by the comparator and setting to an "off" condition to supply the first voltage to the amplifying unit in cases where the level of the amplified signal is lower than the reference voltage as a result of the comparison performed by the comparator.