ISSN 2321 -9017 Volume 11, No.2, February March 202311(2), February – March 2023, 1 - 5 Steve Hung-Lung Tu et al., International Journal of Bio-Medical Informatics- and e-Health,
International Journal of Bio-Medical Informatics and e-Health Available Online at http://www.warse.org/IJBMIeH/static/pdf/file/ijbmieh011122023.pdf https://doi.org/10.30534/ijbmieh/2023/011122023
A Wideband 4-Level Frequency-Shift Keying Demodulator for Biomedical Implants Steve Hung-Lung Tu1, Shih-Yi Chen2 1 stevetu1024@gmail.com 2 g890246@gmail.com
Received Date : January 10, 2023
Accepted Date : February 14, 2023
Published Date : March 07, 2023
2. THE PROPOSED 4-LEVEL FSK DEMODULATOR ABSTRACT The input RF signal is firstly down-converted to IF signal by using a down-conversion mixer and amplified to full-swing signal with an IF OTA. The demodulation is finally performed with a digital demodulator and converted back to digital data. Figure 1 illustrates the block diagram of the proposed 4-level FSK demodulator.
A wideband 4-level frequency-shift keying (FSK) modulation scheme for biomedical implants is investigated and its digital demodulator circuits have been implemented with a 0.18m 1P6M standard CMOS technology process. The application of the implementation technique is transferring data to wireless biomedical implants at a higher data-rate modulation scheme of 4-level FSK. The proposed demodulator circuits have been validated with test chip measurement results. It consumes the power of 7.2mW from a 1.8V supply.
Received 4-level FSK signal
LNA
Mixer
OTA
Digital Demodulator
Data out
Implemented 4-level FSK demodulator
Key words: 4-level FSK, biomedical implants, digital demodulators, CMOS.
Local Oscillator
1. INTRODUCTION
Figure 1: Block Diagram of the Proposed 4-Level FSK Demodulator
A high data-rate transmission is highly desired for the wireless biomedical implants, especially for those that interface with central nervous systems such as cochlears [1]-[5] which requires a large amount of data to simultaneously interface with even more amount of neurons through many channels. For wireless communication standards such as IEEE 802.11a however, the data rate can be as high as 54 Mbps with the expense of high carrier frequency even up to 5.8GHz. However, a high data-rate-to-carrier- frequency ratio with FSK modulation even up to 67% can be found in [6]-[7] at the expense of high frequency deviation (or poor spectrum efficiency) up to 2.5MHz (2-level FSK modulation scheme with 2 carrier frequencies, f1=5MHz for logic “1” and f0=10MHz for logic “0”). In this paper, the 4-level frequency-shift keying (FSK) modulation scheme is utilized, which the better performance in terms of circuit simplicity and higher data-rate can be validated with the proposed circuit experimental results.
2.1 Mixer The received RF signal is down-converted to IF signal with the double-balanced mixer as shown in Figure 2, in which a fully-differential configuration is employed [8]-[9]. It mixes the differential input RF and LO signals and develops the differential output IF signal. In Figure 2, the resonator pairs (L1, C1) and (L2, C2) act as the differential output loads in order to obtain a higher conversion gain. VBP is the bias voltage with bias resistors Rp1 and Rp2. R5 and R6 are the bias resistors providing the maximum DC level for the LO oscillator. The voltage dividers constructed with resistors R1, R2 and R3, R4 bias the differential RF port at 1V. The degenerative resistor RDeg is connected across the path between the current-mirror stages (M1 and M2) and the trans-conductance stages (M3 and M4). Thus, it does not lead to the voltage drop and still has the same linearity enhancement.
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