This paper proposes a novel structure of ASK (amplitude shift keying) demodulators, which requires no external capacitors, for implantable micro-stimulators. By using a traditional β multiplier reference to detect the signal envelope, followed by a Schmitt trigger and a load driver, the large off-chip capacitor in traditional ASK demodulators is not required any more. Therefore, the proposed circuit possesses small area to be integrated in an SOC (system-on-chip). Besides, due to the lack of the large capacitor, the proposed circuit can operate with a higher data rate using lower frequency carriers. The proposed circuit is integrated in an implantable micro-stimulator on silicon using 0.35 μ m 2P4M CMOS process. The area of the proposed circuit occupies merely 0.039 mm2 with a maximum power dissipation of less than 12 mW (including the power consumption of the analog circuits of the micro-stimulator) by measurement results on silicon. Moreover, the measurement results verify that the proposed ASK demodulator can detect the ASK modulated signal up to 570 kbps data rate at 2 MHz carrier frequency when the modulation index is 10%.
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