Super-regenerative receiver at 433 MHz

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Abstract

This paper presents a receiver for operation in the 433 MHz ISM band. The selected architecture explores the super-regeneration phenomena to achieve a high sensitivity for applying in wireless implantable microsystems. This radio-frequency (RF) chip can be supplied with a voltage of only 3 V for demodulating signals with powers in the range (−100, −40) dB. The codulation (modulation and coding) scheme of the binary data is a variation of the Manchester code combined with on/off keying (OOK) modulation. The AMIS 0.7 μm CMOS process was selected for targeting the requirement to fabricate a low-cost receiver, whose prototype was integrated in a die with an area of 5×5 mm2. Also, this receiver is fully compatible with commercial transmitters for the same frequency.

Introduction

Invasive and implantable biomedical devices used for diagnostic and therapy, ranging from neural [1] to video-capsule endoscopy systems [2] are emerging innovative technologies and they are expected to originate significant business activity in the near future. The success of such systems is in part due to the advent of microtechnologies, which made possible the miniaturization of several sensors and actuators, as well their integration with readout and communication electronics. Wireless implantable microsystems constitute a breakthrough in the way the internal pathologies can be treated. This means that the radio-frequency (RF) chips can play an important role. In the context of implantable microsystems, the main contribution of this paper is the presentation of a super-regenerative receiver at 433 MHz. An important advantage inherent to this receiver is to be compatible with transmitters commercially available in the market. In this sequence of ideas, the target application for this receiver is in wireless microsystems for stimulating three nerves of the vertebral column, according to the desire of the patient, who presses a push-button to induce micturition and erection (in the case of males). The solution to send the electrostimulation commands can be a box containing a commercial off-the-shelf emitter module at 433 MHz using the same coding and modulation schemes of the receiver (e.g., codulation scheme [3]). The need for such transmission mode is because an RF chip solution is more suitable and reliable than the traditional approaches because the latest solutions use wires for supplying the implantable devices and for transmitting data to these same devices [4].

Section snippets

The frequency of operation

The selection of a frequency for an implantable device is easy to do. First, the sizes of these devices must be as minimal as possible. In this context and as it is of general knowledge, the antenna is one of the most critical subsystems in wireless communications, which means that the antenna must be small enough to comply with size constraints of the microsystems to not compromise the desired miniaturization. The size reduction can be a problem because the antenna must be designed for

Results

Fig. 7 shows several signals inside the receiver in a response to an RF signal with an amplitude of 100 μV. It is important to note that the differential signal given by the single-ended signal obtained from the difference OUT1–OUT2 is correctly filtered, thus the envelope detection is correctly done. The amplified version, Vsingleout (V), of the single-ended signal is then obtained and gives rise to a pulsed signal in the receiver (which further in conjunction with a coding scheme will allow

Conclusions

This paper presented a super-regenerative receiver at 433 MHz for use in wireless implantable microsystems. The frequency of 433 MHz was selected because it allows the reception of RF signals inside the human body. The receiver can be supplied with a voltage of 3 V and allows the reception of RF signals with powers in the range of [−100, −40] dB. The codulation scheme is based on the on/off keying amplitude (OOK) modulation plus a modified version of the Manchester code (a Biphase code). Despite

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