High-voltage class-D direct-drive audio amplifier for electrostatic loudspeakers

Electrostatic loudspeakers (ESLs) are capable of low distortion and have desirably flat frequency response within the audio frequency range. In this paper, a novel approach is proposed for audio amplification using a high-voltage direct-digital solid-state class-D amplifier as a method that replaces impedance matching ESL audio transformers. Optical coupling is used to achieve isolation from the high-voltage side. The proposed stacked MOSFET output stage provides a solution to the voltage swing limitations of the available switching power MOSFETs. An example digital amplifier having 14-bit ADC precision PWM with f_c = 50 kHz was implemented at ± 375 V delivering 7W into R_a =20kΩ. The digital modulator was realized on a Xilinx Virtex4 Sx35-10ff668 at F_s = 100 MHz clock.