Push-pull output driver and operational amplifier using same

An operational amplifier circuit, comprising:

• an input stage having first and second inputs, which generates a first node voltage at a first circuit node as a function of voltages on the first and second inputs;
• a level shifter directly connected to the first circuit node, which generates a second node voltage on a second circuit node as a function of the first node voltage;
• and
• a first transistor having a control terminal receiving the second node voltage, and connected between a supply voltage and an output node, and a second transistor having a control terminal receiving the first node voltage from the first circuit node, and connected between the output node and a reference voltage, wherein the first and second transistors have a common conductivity type, wherein the level shifter is connected between the supply voltage and the reference voltage, and wherein the first transistor is directly connected to the supply voltage,
• wherein the level shifter includes a third transistor including (i) a control terminal receiving the first node voltage from the first circuit node and (ii) a current carrying node at which the second node voltage is generated, the current carrying node of the third transistor being directly connected to the control terminal of the first transistor,
• wherein the level shifter includes a bias current source including a fourth transistor, the fourth transistor and the third transistor being connected in series between the supply voltage and the reference voltage,
• wherein an input bias on a control terminal of the fourth transistor is generated from a source that is separate and independent from one or more sources influencing the first node voltage generated by the input stage, such that the first node voltage is generated by the input stage independently of the input bias on the control terminal of the fourth transistor, and
• wherein the control terminal of the first transistor is controlled only by the current carrying node of the third transistor and a current carrying path of the fourth transistor.

A voltage driver circuit, comprising:

• an amplifier having a first input and a second input, generating a voltage at a first circuit node based on a difference between voltages applied to the first and second inputs;
• a first transistor connected between a supply voltage and an output node, and having a control terminal, wherein the first transistor is directly connected to the supply voltage;
• a second transistor connected between the output node and a reference voltage, and having a control terminal connected to the first circuit node, wherein the first and second transistors have a common conductivity type;
• a third transistor connected in current mirror relationship with the second transistor, and having (i) a control terminal directly receiving the voltage from the first circuit node and (ii) a first current carrying terminal at which a second voltage is generated, the first current carrying terminal being directly connected to the control terminal of the first transistor;
• and
• a bias current source including a fourth transistor, the fourth transistor and the third transistor being connected in series between the supply voltage and the reference voltage,
• wherein an input bias on a control terminal of the fourth transistor is generated from a source that is separate and independent from one or more sources influencing the voltage generated by the amplifier, such that the voltage is generated by the amplifier independently of the input bias on the control terminal of the fourth transistor.