LOW NOISE AMPLIFIER DESIGN AND NOISE CANCELLATION FOR WIRELESS HEARING AIDS
Wireless technology is one of the most promising approaches for future hearing aids research. Compared to the conventional hearing aids, wireless hearing aids provide a clearer voice, longer operation time, easy communication with other audio devices, and so on. Although the advantages of the wireless hearing aids, noise cancellation and power consumption are still the key issues in research, which require more efficient noise cancellation method and lower power consumption circuit design. Receiving the processed audio signal within the power budget of the wireless hearing aid earpiece is one of the inherent design challenges. Low noise amplifier (LNA) is the first stage to receive the signal, which is embedded in the earpiece of a wireless hearing aid. There has been not much attempts to implement a CMOS receiver for the earpiece of wireless hearing aid systems. As an attempt towards its CMOS implementation, an integrated single-ended CMOS LNA with inductive degeneration at the source is presented. The power consumption is the key issue to concern in this design. Because the earpiece and the body unit for hearing aid device are separated within about one meter, the noise figure and gain is not as important as power consumption. With the small power consumption, the LNA should have good linearity also. According to the normal hearing aid battery capacity, the total power consumption of an earpiece, where receiver is the most power hungry block, should be as low as possible but below 3.0 mW [1]. The recently reported 0.9 GHz CMOS receiver consumes 2.2 mW, out of which LNA alone consumes 1.44 mW [2]. Reducing LNA power consumption will extend the battery life. A single ended low voltage and low power LNA was implemented in CSM 0.18 µm v CMOS technology. The LNA is powered at 1.0 V supply and drains only 0.95 mA. The LNA provides a forward gain of 11.91 dB with a noise figure of only 2.41 dB operating in the 0.9 GHz band. The IIP3 is 0.7 dBm and the P1dB is -12 dBm. The proposed design also meets requirements on noise, linearity and gain for 0.9 GHz low power applications, specifically suitable for CMOS wireless hearing aids. Another consideration in this research work is about canceling the environmental noise. Normally, an input to hearing aids is often associated with the environmental noise. For instance, due to the environmental noise, a hearing-impaired person not only feels severe hearing loss but also is unable to perceive desired speech from the noisy environment. Thus, the noise cancellation is a primary concern, particularly for hearing impaired. In this thesis, a modified two-element beamforming method for noise cancellation is introduced, which helps reduce the surrounding environment noise. This method needs to be verified before physical implementation. So, the behavior model for this method is also presented, which shows a better noise cancellation performance. In addition, the whole wireless hearing aid system is simulated using the proposed noise canceling model. The simulation satisfies the proposed method.