Amplifier circuit and methods of operation thereof
View Patent ↗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.
1. A charge pump circuit having a voltage input for receiving an input voltage, a control input for receiving a control signal and first and second output terminals, wherein said charge pump is able to operate in:
a variable mode to provide output voltages at said first and second output terminals, wherein said output voltages in the variable mode have a relationship with respect to the input voltage that varies based on a control signal such that a first change in the control signal results in a change in output voltage; and alternatively
in a first non-variable mode to provide output voltages at said first and second output terminals having a fixed relationship with respect to an input voltage, wherein in the non-variable mode the output voltages do not vary with any changes in said control signal.
2. A charge pump circuit as claimed in claim 1 wherein said output voltages in the first non-variable mode comprise positive and negative output voltages each substantially equal in magnitude to a fraction of said input voltage.
3. A charge pump circuit as claimed in claim 2 wherein said fraction is substantially a half.
4. A charge pump circuit as claimed in claim 1 wherein said output voltages in the first non-variable mode comprise positive and negative output voltages each substantially equal in magnitude to said input voltage.
5. A charge pump circuit as claimed in claim 1 which is further operable in a second non-variable mode to provide output voltages that have a defined relationship with said input voltage and that differ from said output voltages of the first non-variable mode.
6. A charge pump circuit as claimed in claim 5 wherein
said output voltages in the first non-variable mode are positive and negative output voltages each substantially equal in magnitude to half of said input voltage and wherein
said output voltages in the second non-variable mode are positive and negative output voltages each substantially equal in magnitude to said input voltage.
7. A charge pump circuit as claimed in claim 5 wherein said output voltages in the variable mode vary between the output voltages produced in the first non-variable mode and the output voltages produced in the second non-variable mode.
8. A charge pump circuit as claimed in claim 1 comprising
an input terminal for receiving said input voltage;
output terminals for outputting said output voltage;
at least first and second flying capacitor terminals for connection to at least one flying capacitor; and
a switch network interconnecting said terminals.
9. A power supply circuit comprising a charge pump circuit as claimed in claim 1 and a DC-DC converter configured such that said input voltage of the charge pump circuit is derived from the output of the DC-DC converter.
10. A power supply circuit comprising a charge pump circuit as claimed in claim 1 and a linear regulator configured such that said input voltage of the charge pump circuit is received from an output of the linear regulator.
11. An audio amplifier circuit comprising:
one or more amplification stages; and
a charge pump circuit as claimed in claim 1 wherein said output voltages are provided as power supplies for at least one of said one or more amplification stages.
12. An audio amplifier circuit as claimed in claim 11 wherein said control signal is a volume control signal.
13. An audio apparatus comprising an audio amplifier circuit as claimed in claim 11 .
14. An audio apparatus as claimed in claim 13 wherein the audio apparatus comprises at least one: a portable music system, an MP3 player, a mobile telephone handset, a Hi-Fi, an in-car entertainment system and a DVD player.
15. An amplifier circuit, comprising:
an amplifier for amplifying an input signal based on a volume signal; and
a charge pump circuit for receiving an input voltage and providing first and second output voltages as supply voltages for said amplifier, wherein
the charge pump circuit is able to operate in a first mode wherein the first and second output voltages have a relationship with respect to the input voltage that varies in response to changes in the level of the input signal and/or volume signal and alternatively in a second mode wherein the first and second output voltages have a fixed relationship with the input voltage and do not vary in response to changes in the level of the input signal and/or volume signal.
16. A method of generating output voltages from an input voltage using a charge pump circuit having a voltage input for receiving the input voltage, a control input for receiving a control signal and first and second output terminals, the method comprising the steps of:
operating the charge pump in a variable mode to provide output voltages at the first and second output terminals wherein said output voltages in the variable mode have a relationship with respect to the input voltage that varies based on a control signal such that a first change in the control signal results in a change in output voltage; and alternatively
operating the charge pump in a first non-variable mode to provide output voltages at the first and second output terminals having a first defined relationship with an input voltage, wherein, in the non-variable mode, the output voltages do not vary with any changes in said control signal.
17. A method of amplifying an input signal comprising the steps of generating output voltages as claimed in claim 16 and supplying said output voltages as power supply voltages to an amplifier circuit.