: This paper presents a wideband frequency-shift keying (FSK) demodulator suitable for a digital data transmission chain of wireless neural stimulation microsystems such as cochlear implants and retinal prostheses. The demodulator circuit derives a constant frequency clock directly from an FSK carrier, and uses this clock to sample the data bits. The circuit occupies 0.03 mm2 using a 0.6 ?m, 2M/2P, standard CMOS process, and consumes 0.25 mW at 5 V. This circuit was experimentally tested at transmission speed of up to 2.5 Mbps while receiving a 5~10 MHz FSK carrier signal in a cochlear implant system. Key words: Biomedical implants, CMOS, Demodulator, Frequency-shift keying (FSK), Cochlear implant doi:10.1631/jzus.2006.A1056 Document code: A CLC number: TN76