Multiple-voltage supply power amplifier with dynamic headroom control

A method for controlling an output buffer stage of a monolithic integrated circuit amplifier that includes a first, lower voltage power supply and a second, higher voltage power supply, comprising the following steps:

• providing a first current to the output buffer stage substantially wholly from the first voltage supply when an output demand voltage is less than a predetermined switch-over threshold;
• providing a second current to the output buffer stage substantially wholly from the second voltage supply when the output demand voltage is greater than the switch-over threshold;
• and
• providing a voltage at a second current terminal of the output buffer stage that is greater than the voltage at a first current terminal of the output buffer stage by a controlled headroom voltage at and above a switch-over voltage, said headroom voltage increasing gradually with increasing output voltage up to a maximum amount at maximum output voltage, thereby dynamically controlling the voltage headroom of the output buffer stage, that is, the voltage difference between the first and second current terminals.

A monolithic integrated circuit amplifier having an amplifier input signal and an amplifier output signal comprising:

• a gain stage that has a gain stage output signal and has, as an input, the amplifier input signal;
• an output buffer stage having, as its output signal the amplifier output signal, as its input signal, the gain stage output signal;
• and having at least a first power output transistor, which has first and second current terminals and a current control terminal;
• a first and a second voltage supply, the second voltage supply having a relatively higher magnitude than the first;
• a first power control circuit connected to both the first and second voltage supplies, and to the output buffer stage through a regulator bus;
• the first power control circuit including voltage headroom control means for setting a voltage headroom at a switch-over voltage and at the maximum value of the amplifier output signal, the voltage headroom being defined as the voltage available at the second current terminal of the first power output transistor relative to the first current terminal of the first power output transistor;
• first control path circuitry connected between the first voltage supply and the regulator bus;
• and
• second switching circuit control path circuitry connected between the second voltage supply and the regulator bus;
• in which:
• when an output demand voltage is less than a predetermined switch-over threshold:
• current to the output buffer stage is provided substantially from the first voltage supply via the first control path circuitry;
• and
• the voltage on the regulator bus itself substantially blocks current output from the second control path circuitry;
• and
• when the output demand voltage is greater than the switch-over threshold:
• current to the output buffer stage is provided substantially from the second voltage supply, via the second control path circuitry;
• and
• the voltage headroom increases gradually with increasing output voltage up to a maximum amount at maximum output voltage;
• the voltage on the regulator bus itself substantially blocking current output from the first control path circuitry;
• and
• the voltage headroom control means includes:
• an output voltage detecting means for detecting the amplifier output signal voltage and for converting the amplifier output signal voltage into a first current;
• an output voltage threshold means for establishing a voltage threshold above which the first current output from the output voltage detecting means increases with output voltage;
• and
• a current coupling means for receiving the first current and for providing a current to a voltage shifting means that is proportional to the first current;
• the voltage shifting means being provided for receiving the current signal from the current coupling means and for converting the current signal from the current coupling means to a portion of the control voltage that is proportional to the current signal and for converting the current signal into a voltage headroom control voltage.

An integrated circuit comprising:

• A) a single semiconductor chip;
• B) a plurality of monolithic IC amplifiers fabricated on the single semiconductor chip, each amplifier including:
• i) a gain stage that has a gain stage output signal and has, as an input, an amplifier input signal;
• ii) an output buffer stage having, as its output signal, the amplifier output signal, as its input signal, the gain stage output signal and having at least a first power output transistor, which has:
• a) first and second current terminals controlling the headroom of the output buffer stage, that is, the voltage between the first and second power current terminals, and
• b) a current control terminal;
• C) a first and a second voltage supply, the second voltage supply having a relatively higher magnitude than the first;
• D) a first power control circuit connected to both the first and second voltage supplies, and to the output buffer stage through a regulator bus;
• E) first control path circuitry connected between the first voltage supply and the regulator bus;
• and
• F) second control path circuitry connected between the second voltage supply and the regulator bus;
• in which:
• when an output demand voltage is less than a predetermined switch-over threshold, current to the output buffer stage is provided substantially from the first voltage supply via the first control path circuitry;
• and
• when the output demand voltage is greater than the switch-over threshold, current to the output stage is provided substantially from the second voltage supply via the second control path circuitry;
• each amplifier further comprises a respective headroom control means for dynamically controlling a voltage headroom of the output stage, that is, the voltage between the first and second power current terminals, and, as the output demand voltage increases above the switch-over threshold, for increasing the voltage headroom.