Piezoelectric tubular positioners that drive manipulators in scanning tunneling microscopes require high-voltage, low-current drive circuits. The circuit in Figure 1 can drive high-resistance, low-capacitance piezoelectric loads at a –3-dB bandwidth of 6 kHz. It offers a low-cost alternative to commercial drivers. Transistors Q₃ and Q₄ form a current mirror, with R₃ setting Q₄'s collector current as the following equation determines: I_C3=I_C4=[V_CC–(–V_CC)–V_BE(Q₄)]/R₃. Operational amplifier IC₁ provides base drive to Q₅, which in turn drives Q₆. With no signal applied to IC₁'s input, the collector currents of Q₆ and Q₃ balance, and the output taken from the junction of emitter followers Q₁ and Q₂ rests at 0V.

Applying an input signal to IC₁ drives its output toward the positive or the negative 12V supply rail. Allowing IC₁'s output to saturate would introduce sufficient slew-rate delay to cause oscillations. Although specifying a relatively fast operational amplifier, an LF411, improves the amplifier's bandwidth and slew rate, antiparallel diodes D₁ and D₂ improve stability by restricting IC₁'s output excursion to one diode forward-voltage drop.

You can adjust R₇ to minimize output dc offset voltage and slew rate. As a rule of thumb, select resistor R₇ to be twice the value of R₉. The ratio of R₉ to R₈ sets the amplifier's gain. Figure 2 shows the input and output waveforms using optimal values for R₇ and R₉. Note that the V_CEO ratings for Q₁ and Q₂ limit V_CC and –V_CC to 300V or less.

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