Patent ID: 6417736
Filing Date: 2002-07-09
Classification: H03F,H04L

Abstract:
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: 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; and the second control path circuitry provides, via the regulator bus, a headroom voltage over the output transistor that increases gradually with increasing output voltage up to a maximum amount at a maximum output voltage, the headroom voltage being defined as the voltage difference between a second current terminal of the output transistor and a first current terminal of the output transistor, the second current terminal being connected to the regulator bus; and the voltage on the regulator bus itself substantially blocks current output from the first control path circuitry.