# US 5,708,393 A · High voltage operational amplifier output stage

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- Number: US 5,708,393 A
- Document ID: US5708393A
- Status: Granted
- Kind: A
- Application number: 08/662,158
- Filed: 1996-06-12
- Granted: 1998-01-13
- Earliest claimed: 1995-06-24
- Assignees: Motorola, Inc.
- Inventors: Thien Huynh Luong; Hienz Lehning
- Web page: https://patentgrep.com/patent/US5708393A

## CPC

- H03F 3/3001: {with field-effect transistors}
- H03F 3/42: Amplifiers with two or more amplifying elements having their DC paths in series with the load, the control electrode of each element being excited by at least part of the input signal, e.g. so-called totem-pole amplifiers
- H03F 3/423: {with MOSFET's}
- H03F: AMPLIFIERS

## Abstract

A current sourcing output stage for a high voltage operational amplifier receives a low voltage input signal (V.sub.IN) and provides a high current output signal corresponding to the low voltage input signal at an output terminal (8). A first PNP transistor (Q1) is coupled between a voltage supply (V.sub.CC) and a plurality of cascaded PNP transistors (Q2, Q3, Q8-Q11) coupled to the output terminal (8). The base of the first PNP transistor (Q1) is coupled to receive the input signal (V.sub.IN) and the bases of the cascaded PNP transistors are coupled to receive different bias voltages A control circuit (Q5-Q7, R1-R5) is coupled to the voltage supply (V.sub.CC) and has an input coupled to the output terminal (8) for deriving a plurality of bias voltages and to the cascaded PNP transistors (Q2, Q3, Q8-Q11) to supply the bias voltages to the respective bases of the cascaded PNP transistors, so that the cascaded PNP transistors (Q2, Q3, Q8-Q11) are biased by bias voltages dependent on the voltage swing of the output signal.

## Claims

### Claim 1

A current sourcing output stage for a high voltage operational amplifier, the output stage comprising:
an input terminal for receiving a low voltage input signal;
an output terminal for providing a high current output signal corresponding to the low voltage input signal;
a first PNP transistor coupled between a voltage supply terminal and a plurality of cascaded PNP transistors coupled to the output terminal, the base of the first PNP transistor being coupled to the input terminal and the of the bases of the cascaded PNP transistors being coupled to receive different bias voltages; and
a control circuit coupled to the voltage supply terminal and having an input coupled to the output terminal for deriving a plurality of bias voltages and to the cascaded PNP transistors to supply the bias voltages to the respective bases of the cascaded PNP transistors, whereby the cascaded PNP transistors are biased by bias voltages dependent on the voltage swing of the output signal.

### Claim 2 (depends on 1)

A current sourcing output stage according to claim 1, further comprising a resistive voltage divider network coupled between the input and the voltage supply terminal to provide the plurality of bias voltages and a plurality of Darlington networks respectively coupled between the resistive voltage divider network and the respective bases of the cascaded PNP transistors to buffer the bias voltages thereto, each Darlington network being formed of a plurality of devices.

### Claim 3 (depends on 2)

A current sourcing output stage according to claim 2, further comprising a plurality of diodes coupled between the resistive voltage divider network and the voltage supply terminal, the number of diodes being equal to the number of devices in each Darlington network plus one.

### Claim 4 (depends on 1)

A current sourcing output stage according to claim 1, further comprising a diode coupled between the output terminal and the input of the control circuit.

### Claim 5 (depends on 1)

A current sourcing output stage according to claim 1, further comprising a clamping circuit coupled between the input of the control circuit and the voltage supply terminal via a reference voltage source, thereby allowing the cascaded PNP transistors to go into saturation.

### Claim 6 (depends on 1)

A current sourcing output stage according to claim 1, wherein all the devices utilised in the amplifier output stage are formed in low voltage processes and the amplifier output stage has low output saturation.