Operational amplifier, corresponding circuit, apparatus and method

A circuit, comprising:

• a drive device including an amplifier, the amplifier including:
• an input terminal and an output terminal;
• an input stage coupled to the input terminal;
• an output stage coupled to the output terminal;
• a gain node;
• a bias current source that is selectively coupled to the input stage to supply a bias current to the input stage;
• a current mirror circuit coupled to the gain node, the current mirror circuit in operation mirroring the bias current supplied to the input stage to generate at least one mirrored bias current and in operation supplying the at least one mirrored bias current to the gain node and to the output stage;
• a first switch circuit including a node coupled to receive a pre-bias voltage and being coupled to the gain node, the first switch circuit in operation, in response to being activated, coupling the gain node to the pre-bias voltage and isolating the gain node from node receiving the pre-bias voltage in response to being deactivated;
• a second switch circuit coupled to the output stage and that in operation, in response to being deactivated, deactivate the output stage;
• and
• a third switch circuit coupled to the output terminal and that in operation, in response to being activated, couples the output terminal to a node coupled to receive a reference voltage and that in operation, in response to being deactivated, isolates the output terminal from the node receiving the reference voltage;
• and
• a load coupled to the output terminal.

A method, comprising:

• switching an amplifier alternately between an active state and a non-active states the amplifier including an input stage, and output stage having an output, and a gain node;
• in said active state,
• providing a bias current to said input stage
• mirroring the bias current to supply a mirrored bias current to the gain node and to the output stage;
• and
• in said non-active state,
• terminating the providing of the bias current to the input stage;
• driving the gain node to a pre-bias voltage;
• deactivating the output stage;
• driving the output of the output stage to a reference voltage level.