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 comprising:
first and second output nodes for connection to respective first and second reservoir capacitors and for outputting respective first and second output voltages;
nodes for connecting to n flying capacitors, where n is a positive integer; and
a switch network for interconnecting said nodes wherein said switch network is configured, in one mode, to operate in a sequence such that said first output voltage is substantially +V/(n+1) and said second output voltage is substantially −V/(n+1) wherein V is an input voltage relative to a common voltage.
2. A charge pump circuit as claimed in claim 1 wherein n>1.
3. A charge pump circuit as claimed in claim 1 wherein said switch network is operable in at least one other mode, to operate in a sequence such that said first output voltage is substantially +V/m and said second output voltage is substantially −V/m where m is an integer between 1 and n inclusive.
4. A charge pump circuit as claimed in claim 3 wherein said circuit is operable in a plurality of other modes.
5. A charge pump circuit as claimed in claim 4 wherein the value of m is different in each of said other modes.
6. A charge pump circuit as claimed in claim 3 wherein the mode of operation is selected by a control signal.
7. A charge pump circuit as claimed in claim 1 wherein, in said one mode, said sequence of operation of the switch network comprises:
a first switch state wherein, in use, said flying capacitors are connected in series with said first reservoir capacitor and in parallel with the input voltage; and
a second switch state wherein, in use, a flying capacitor is connected in parallel with the second reservoir capacitor.
8. A charge pump circuit as claimed in claim 7 wherein said sequence of operation further comprises a third state wherein, in use, said first reservoir capacitor is connected in parallel with a flying capacitor.
9. An audio amplifier circuit comprising:
one or more amplification stages; and
a charge pump circuit as claimed in claim 1 wherein said first and second output voltages are provided as power supplies for at least one of said one or more amplification stages.
10. An audio amplifier circuit comprising:
one or more amplification stages; and
a charge pump circuit as claimed in claim 6 wherein said first and second output voltages are provided as power supplies for at least one of said one or more amplification stages;
wherein said control signal is a volume control signal.
11. An audio apparatus comprising an audio amplifier circuit as claimed in claim 9 .
12. An audio apparatus as claimed in claim 11 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.
13. A charge pump circuit comprising:
input nodes for connection to an input voltage and a common voltage;
first and second output nodes for connection to respective first and second reservoir capacitors and for outputting respective first and second output voltages;
nodes for connecting to one or more flying capacitors; and
a switch network for interconnecting said nodes wherein said switch network is configured, in one mode, to operate to connect the nodes so that, in use, each of said one or more flying capacitors is connected between the input voltage and the common voltage in series with one of said first and second reservoir capacitors.