An accuracy improved hearing aid readout circuit using a gain-enhanced and OTA-free pseudo-PLL feedback technique

Abstract

We present an accuracy improved hearing aid readout circuit using a gain-enhanced and OTA-free pseudo-PLL feedback technique. Compared with the conventional techniques, the technique replaces the typical oscillation approaches with a special pseudo-PLL feedback loop, which is able to partially amplify and directly convert the acoustic signal into the PWM signal without OTAs and comparators. Since the partially amplifying pseudo-PLL loop has the large open loop gain characteristic with the ultra low supply voltage, the accuracy of the large output signal should be maintained with the limited power dissipation. Fabricated with a 0.18 µm standard CMOS process, with the 1.2 V supply voltage and the input sine wave 1 KHz, the signal to noise and distortion rate (SNDR) achieves 55 dB@1 V_p-p output voltage with the bandwidth 20 kHz. Moreover, the circuit’s power consumption is 9 µW.