Amplifier circuit and methods of operation thereof

Abstract: A signal amplifying circuit and associated methods and apparatuses, the circuit comprising: a signal path extending from an input terminal to an output terminal, a gain controller arranged to control the gain applied along the signal path in response to a control signal; an output stage within the signal path for generating the output signal, the output stage having a gain that is substantially independent of its supply voltage, and a variable voltage power supply comprising a charge pump for providing positive and negative output voltages, the charge pump comprising a network of switches that is operable in a number of different states and a controller for operating the switches in a sequence of the states so as to generate positive and negative output voltages together spanning a voltage approximately equal to the input voltage. (end of abstract)

Amplifier circuit and methods of operation thereof description/claims

Brief Patent Description

Full Patent Description

Patent Application Claims

The present invention relates to circuitry for improving the efficiency of an amplifier. The invention further relates to a method for improving the efficiency of an amplifying circuit.

When receiving information signals, such as audio signals for example, for outputting to one or more transducers, such as a speaker for example, the information signals generally need to be adjusted in amplitude. One method of achieving this adjustment includes using a control signal, an example of such a signal being a gain control signal, which varies the gain, and thus the amplitude, of the information signal prior to outputting to the transducer.

FIG. 1 illustrates an example of a known amplifier 10.

The amplifier 10 comprises a gain controller 20; an output stage 40; and a power supply 60.

The gain controller 20 receives an input information signal S1 and an input control signal S2. The control signal S2 controls the gain controller 20 that outputs a gain controlled information signal S3 which is fed as an input signal into the output stage 40. The output stage 40 outputs an output signal S4 that is used to drive a load 70.

The output stage 40 and the gain controller 20 are supplied by the power supply 60 which takes power from some external power source and supplies dual, fixed level, supply voltages +V1 and −V1.

The amplitude of the output signal S4 that drives the load 70 is varied i.e. amplified or attenuated, in response to the control input signal S2, by the combined gain of the gain controller 20 and output stage 40.

The power efficiency of the amplifier 10, i.e. the ratio of the power delivered to the load to the power taken from the power source, is an important parameter of the amplifier. It impacts both power consumption, which is important in battery-powered systems for example, and power dissipation, which influences cost in terms of heatsinking for example.

There are thus advantages in methods and circuits for improving the efficiency of amplifiers such as amplifier 10.

In a first aspect of the invention there is provided a signal amplifying circuit comprising:

- A main input terminal for receiving an input signal;
- A main output terminal for outputting an output signal;
- a signal path extending from the main input terminal to the main output terminal;
- a gain controller arranged to control the gain applied along the signal path in response to a control signal;
- an output stage within the signal path for generating the output signal, the output stage having a gain that is substantially independent of its supply voltage,
- a variable voltage power supply comprising a charge pump circuit for providing a plurality of output voltages, the charge pump circuit comprising:
  - an supply input terminal and a common terminal for connection to an input voltage,
  - first and second supply output terminals for outputting the plurality of output voltages, the supply output terminals in use being connected to the common terminal via respective first and second reservoir capacitors,
  - first and second flying capacitor terminals for connection to a flying capacitor,