A disclosed amplifier and buffer circuit, for example for a linear voltage
regulator, comprises an input gain stage, an integrator and a unity-gain
output stage. An output stage compensation scheme enables stable
operation over a broad range of output capacitance. For low to moderate
output capacitance, the design of the output stage effectively pushes the
output pole to high frequencies while an internal pole provided by the
integrator is dominant and rolls off the gain at lower frequencies. For
high output capacitance, an input impedance of the buffer couples the
internal pole and output pole, such that the output pole becomes dominant
while the internal pole gets pushed to higher frequencies, maintaining
stability. This input impedance connection may utilize the base-emitter
resistance of a bipolar junction transistor connected to the internal
node, or the connection may use an MOS transistor and a separate RC
circuit.