Piezoelectric transducers find use in NDE (nondestructive-evaluation) applications. The PVDF (polyvinylidene-fluoride) transducer has many advantages, including a wide bandwidth and high sensitivity. These transducers require high-voltage and wide-bandwidth amplifiers. The basis of the circuit in Figure 1 is an earlier Design Idea (Reference 1). The operation of the circuits is basically the same, but this one can drive a 2.3-nF capacitive load at frequencies as high as 500 kHz.

In this circuit, an LM7171 op amp from National Semiconductor replaces the LF411, also from National Semiconductor, of the earlier design. The LM7171 op amp has a unity-gain bandwidth of 200 MHz. To further improve the bandwidth, this design’s mirror circuit uses lower-value resistors to increase the current in the transistors, thus increasing the bias current and the power dissipation of Q₃ and Q₄. To improve thermal stability, this design adds resistors R₁₆ and R₁₇, and, to increase the current to drive the transducer’s capacitive load, this design adds a current driver to the circuit’s output. V_CC and V_EE are 15 and –15V, respectively, and V_H+ and V_H– are a maximum of 150 and –150V, respectively.