A fully integrated audio amplifier in flexible a-IGZO TFT technology for printed piezoelectric loudspeakers

This paper presents the design, implementation and characterization of an integrated power efficient cascode amplifier in a flexible a-IGZO thin-film transistors (TFTs) with minimum channel lengths of 25 μm. The circuit consists of a two-stage cascode amplifier for the audio baseband amplification and a source-follower as a buffer to drive printed loudspeakers. The proposed amplifier is fabricated on a 50 μm-thick flexible polyimide foil, and characterized with a 20 V dc supply voltage (V_DD) and an output load capacitance of 15 pF. The measured voltage gain exceeds 15 dB from 4.5 kHz to 15 dB at 25 kHz. The measured 3 dB bandwidth of the unloaded audio amplifier spans from 2.2 kHz to 60 kHz. The amplifier consumes a dc power of 40 mW and delivers 10 dBV of output signal at the 1 dB compression point; this is sufficient to drive printed piezoelectric loudspeakers. The simulated frequency response of the loaded amplifier shows that the amplifier can drive a wide range of capacitive loads from 15 pF to 500 nF. The simulated 3 dB bandwidth of the amplifier loaded with the printed loudspeaker is 29 kHz.