Baseband amplifiers in a-IGZO TFT technology for flexible audio systems

This work shows two baseband amplifiers, which are suitable for audio system applications. The amplifiers are implemented in a flexible a-IGZO thin-film transistor (TFT) technology. They should be capable of driving printed piezoelectric loudspeakers. One of these circuits is a two-stage cascode amplifier, which is operating at 6 V DC supply voltage (VDD). It has a voltage gain of 31 dB over a 3 dB bandwidth of 252 kHz with a DC power consumption as low as 1.5 mW. This amplifier is used as a pre-audio amplifier for driving the audio amplifier. The audio amplifier is a two-stage common-source (CS) circuit with a source-follower stage as a buffer, and is characterized with an 18 V VDD. The measured voltage gain of audio amplifier is 21.5 dB with a 3 dB bandwidth of 55 kHz from a DC power of 30 mW. The simulation of frequency responses of these circuits shows that the amplifiers can drive the loudspeakers with areas of 16 cm2 and 128 cm2. The load of this audio system is the model of printed loudspeaker with specific characterizations of manufacturer.