Described are various techniques that can minimize the use of high-voltage devices in a unity-gain buffer that can be used in a high voltage application, while providing a circuit that generates an output that is an accurately buffered version of the input.

A buffer circuit includes a first transistor, a second transistor, and a third transistor. The first transistor includes a first current terminal, a second current terminal, and a control terminal. The first current terminal is coupled to a load terminal. The control terminal is coupled to a preamplifier input terminal. The second transistor includes a first current terminal and a second current terminal. The first current terminal of the second transistor is coupled to the second current terminal of the first transistor. The third transistor includes a first current terminal, a second current terminal, and a control terminal. The first current terminal of the third transistor is coupled to the load terminal. The second current terminal of the third transistor is coupled to a ground terminal. The control terminal of the third transistor is coupled to second current terminal of the second transistor.

An apparatus, such as a coherent optical receiver, includes a transimpedance amplifier (TIA) with differential outputs, and a multi-tanh type current limiter connected across the differential outputs of the transimpedance amplifier. The multi-tanh type current limiter includes two tanh-type current limiters shifted in voltage and connected to subtract an output current thereof from an output current of the TIA.

A circuit includes a first transistor having a first current terminal, a second current terminal, and a control terminal, the first current terminal coupled to an output terminal, and the control terminal coupled to an input terminal, a second transistor having a first current terminal, a second current terminal, and a control terminal, the first current terminal coupled to the second current terminal of the first transistor, a third transistor having a first current terminal, a second current terminal, and a control terminal, the first current terminal coupled to the output terminal, and the control terminal coupled to the second current terminal of the second transistor, and a fourth transistor having a first current terminal and a control terminal, the first current terminal coupled to the second current terminal of the second transistor, and the control terminal coupled to the second current terminal of the third transistor.

Described are various techniques that can minimize the use of high-voltage devices in a unity-gain buffer that can be used in a high voltage application, while providing a circuit that generates an output that is an accurately buffered version of the input.