Slew rate boost circuitry and method

A method of operating a differential input circuit to provide slew boost currents to an output circuit, comprising:

• (a) providing a differential current steering circuit including a first transistor having a gate coupled to receive a first input signal, a second transistor having a gate coupled to receive a second input signal, and a constant current source coupled to sources of the first and second transistors, and providing first and second outputs of the differential input circuit coupled to the first and second transistors, respectively;
• (b) operating a first slew current circuit of the differential input circuit in response to the first input signal to produce a first slew boost current and introducing the first slew boost current into a current summing conductor coupled to the sources of the first transistor and second transistor and the constant current source;
• (c) operating a second slew current circuit of the differential input circuit in response to the second input signal to produce a second slew boost current and introducing the second slew boost current into the current summing conductor, the first and second slew boost currents boosting currents flowing through the second and first transistors, respectively;
• and
• (d) conducting the currents flowing through the first and second transistors through the first and second output conductors, respectively, to the output circuit.

A differential input circuit for providing slew boost currents to an output circuit, the differential input circuit comprising:

• (a) a differential current steering circuit including a first input transistor having a gate coupled to receive a first input signal, a second input transistor having a gate coupled to receive a second input signal, and a tail current source coupled to sources of the first and second input transistors, the first and second input transistors having drains connected to first and second outputs of the differential input circuit, respectively;
• (b) a first sensing transistor having a gate coupled to the gate of the first input transistor, and a drain coupled to a first supply voltage conductor, and a second sensing transistor having a gate coupled to the gate of the second input transistor, and a drain coupled to the first supply voltage conductor;
• (c) a first amplifying circuit having an input coupled to the source of the first sensing transistor and a first output coupled to control the tail current source to increase the flow of current into a first conductor coupled to the sources of the first and second input transistors;
• and
• (d) a second amplifying circuit having an input coupled to the source of the second sensing transistor and a first output coupled to control the tail current source to increase the flow of current into the first conductor.

A differential input circuit for providing slew boost currents to an output circuit, the differential input circuit comprising:

• (a) a differential current steering circuit including a first transistor having a gate coupled to receive a first input signal, a second transistor having a gate coupled to receive a second input signal, and a constant current source coupled to sources of the first and second transistors, the first and second transistors having drains connected to first and second outputs of the differential input circuit, respectively;
• (b) a first slew current circuit including a third transistor having a gate coupled to the gate of the first transistor, and a drain coupled to a first supply voltage conductor, a fourth transistor having a first electrode coupled to a source of the third transistor, and a second electrode and a control electrode coupled to a second constant current source, and a fifth transistor having a control electrode coupled to the control electrode of the fourth transistor, a first electrode coupled by a first conductor to the source of the first transistor, and a second electrode coupled to a third output of the differential input circuit;
• and
• (c) a second slew current circuit including a sixth transistor having a gate coupled to the gate of the second transistor, a drain coupled to the first supply voltage conductor, a seventh transistor having a first electrode coupled to a source of the sixth transistor, and a second electrode and a control electrode coupled to a third constant current source, and an eighth transistor having a control electrode coupled to the control electrode of the seventh transistor, a first electrode coupled by the first conductor to the source of the second transistor, and a second electrode coupled to a fourth output of the differential input circuit.

An operational amplifier comprising:

• (a) a differential input circuit for providing slew boost currents, the differential input circuit including
• i. a differential current steering circuit including a first transistor having a gate coupled to receive a first input signal, a second transistor having a gate coupled to receive a second input signal, and a constant current source coupled to sources of the first and second transistors, the first and second transistors having drains connected to first and second outputs of the differential input circuit, respectively,
• ii. a first slew current circuit including a third transistor having a gate coupled to the gate of the first transistor and a drain coupled to a first supply voltage conductor, a fourth transistor having a first electrode coupled to a source of the third transistor, and a second electrode and a control electrode coupled to a second constant current source, and a fifth transistor having a control electrode coupled to the control electrode of the fourth transistor, a first electrode coupled by a first conductor to the source of the first transistor, and a second electrode coupled to a third output of the differential input circuit,
• iii. a second slew current circuit including a sixth transistor having a gate coupled to the gate of the second transistor, a drain coupled to the first supply voltage conductor, a seventh transistor having a first electrode coupled to a source of the sixth transistor, and a second electrode and a control electrode coupled to a third constant current source, and an eighth transistor having a control electrode coupled to the control electrode of the seventh transistor, a first electrode coupled by the first conductor to the source of the second transistor, and a second electrode coupled to a fourth output of the differential input circuit;
• and
• (b) an output circuit including a pull-up transistor coupled to at least one of the third and fourth outputs of the differential input circuit, and a pull-down transistor coupled to at least one of the first and second outputs of the differential input circuit.