High-Voltage High Input Impedance Unity-Gain Voltage Buffer

M. Jankowski, A. Napieralski
Technical University of Lodz, PL

Keywords: high-voltage, unity-gain buffers, current-mode signals

Summary:

The research presented in this paper is targeted to devise possibly non-complex high-voltage unity-gain buffer well suited for connecting to outputs of current-mode stages. The circuit idea originated from need of buffering a high-voltage current-mode waveform generator. Structures well-suited for acting as high-voltage unity-gain buffers are symmetrical voltage followers. Source-input followers offer higher precision of voltage gain, but have limited input impedance. Gate-input follower, seems to provide a solution, but offers non-precise voltage gain value. The circuit proposed in this paper is similar to gate-input followers. The buffer has special current-biasing circuitry which provides input stage current tuned to cause almost equal voltage drops on transistors of input and output stage. Thus, it offers voltage-gain close to unity and very high input impedance. After a modification, the parts of the circuit that are crucial for quality of its output signals, consist of low-voltage MOS devices shielded by high-voltage devices. The proposed buffer structure is designed and simulated in 0.8um SOI process. The buffer has reasonably simple structure in comparison to proposed buffer structures. It can work in high-voltage systems, driven by both voltage-mode and current-mode preceding stages.