An amplifier including a P-channel transistor having current terminals coupled between a first node and a second node and having a control terminal coupled to a third node receiving an input voltage, an N-channel transistor having current terminals coupled between a fourth node developing an output voltage and a supply voltage reference and having a control terminal coupled to the second node, a first resistor coupled between the first node and a supply voltage, a second resistor coupled between the first and fourth nodes, and a current sink sinking current from the second node to the supply reference node. The amplifier may be converted to differential form for amplifying a differential input voltage. Current devices may be adjusted for common mode, and may be moved or added to improve headroom or to improve power supply rejection. Chopper circuits may be added to reduce 1/f noise.

An amplifier including a P-channel transistor having current terminals coupled between a first node and a second node and having a control terminal coupled to a third node receiving an input voltage, an N-channel transistor having current terminals coupled between a fourth node developing an output voltage and a supply voltage reference and having a control terminal coupled to the second node, a first resistor coupled between the first node and a supply voltage, a second resistor coupled between the first and fourth nodes, and a current sink sinking current from the second node to the supply reference node. The amplifier may be converted to differential form for amplifying a differential input voltage. Current devices may be adjusted for common mode, and may be moved or added to improve headroom or to improve power supply rejection. Chopper circuits may be added to reduce 1/f noise.

An operational amplifier comprises: a first amplifier stage 4 comprising a first differential pair of transistors 8, 10 arranged to receive and amplify a differential input signal 18, 20 thereby providing a first differential output signal 22, 24; and a second amplifier stage 6 comprising a second differential pair of transistors 26, 28 arranged to receive and amplify the first differential output signal 22, 24 thereby providing a second differential output signal 38, 40.

A high gain differential amplifier includes first through eighth transistors, first through third degeneration resistors, and first through third current sources. The fourth and fifth transistors form a p-type metal-oxide-semiconductor (PMOS) transistor pair. Further, the second and eighth transistors form a current mirror circuit. The PMOS transistor pair and the current mirror circuit form a common mode feedback circuit. The high gain differential amplifier controls the common-mode output voltage with the common mode feedback circuit and a reference voltage.

An operational amplifier comprises: a first amplifier stage 4 comprising a first differential pair of transistors 8, 10 arranged to receive and amplify a differential input signal 18, 20 thereby providing a first differential output signal 22, 24; and a second amplifier stage 6 comprising a second differential pair of transistors 26, 28 arranged to receive and amplify the first differential output signal 22, 24 thereby providing a second differential output signal 38, 40.

A high gain differential amplifier includes first through eighth transistors, first through third degeneration resistors, and first through third current sources. The fourth and fifth transistors form a p-type metal-oxide-semiconductor (PMOS) transistor pair. Further, the second and eighth transistors form a current mirror circuit. The PMOS transistor pair and the current mirror circuit form a common mode feedback circuit. The high gain differential amplifier controls the common-mode output voltage with the common mode feedback circuit and a reference voltage.

To perform a rail-to-rail input operation, provided is a differential amplifier circuit including a first differential input pair and a second differential input pair which has a threshold value different from that of the first differential input pair. Both the differential input pairs do not operate at the same time. A transistor is connected between the first differential input pair and a current source to achieve a configuration in which the first differential input pair and the second differential input pair do not operate at the same time.

Telescopic amplifier circuits are disclosed. In an embodiment, a telescopic amplifier includes an input stage for receiving differential input signals, an output stage for outputting differential output signals at the drains of a first output transistor and a second output transistor, a tail current transistor coupled to sources of a first input transistor and a second input transistor, a common mode feedback circuit coupled to the differential output signals and outputting a common mode output signal, and a circuit element coupled between the common mode output signal and a gate of the tail current transistor. In an embodiment the circuit element is a resistor. In another embodiment the circuit element is a source follower transistor. In additional embodiments a phase margin of the common mode feedback open loop gain of the amplifier is determined by the value of the resistor. Additional embodiments are disclosed.

Telescopic amplifier circuits are disclosed. In an embodiment, a telescopic amplifier includes an input stage for receiving differential input signals, an output stage for outputting differential output signals at the drains of a first output transistor and a second output transistor, a tail current transistor coupled to sources of a first input transistor and a second input transistor, a common mode feedback circuit coupled to the differential output signals and outputting a common mode output signal, and a circuit element coupled between the common mode output signal and a gate of the tail current transistor. In an embodiment the circuit element is a resistor. In another embodiment the circuit element is a source follower transistor. In additional embodiments a phase margin of the common mode feedback open loop gain of the amplifier is determined by the value of the resistor. Additional embodiments are disclosed.

Telescopic amplifier circuits are disclosed. In an embodiment, a telescopic amplifier includes an input stage for receiving differential input signals, an output stage for outputting differential output signals at the drains of a first output transistor and a second output transistor, a tail current transistor coupled to sources of a first input transistor and a second input transistor, a common mode feedback circuit coupled to the differential output signals and outputting a common mode output signal, and a circuit element coupled between the common mode output signal and a gate of the tail current transistor. In an embodiment the circuit element is a resistor. In another embodiment the circuit element is a source follower transistor. In additional embodiments a phase margin of the common mode feedback open loop gain of the amplifier is determined by the value of the resistor. Additional embodiments are disclosed.