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This work proposes a direct sequence spread spectrum transmitter with high transmission range and efficiency for audio signals. It is shown that by choosing high process gain for spread spectrum signal the data could reach a range of 55km in the 2.4GHz ISM band. By employing a light modulation scheme, we have a relaxed SNR requirement for having a low bit error rate (BER) which translates to relaxed error vector magnitude (EVM) condition. Therefore a switching power amplfier (PA) is used in this work which improves the transmitter’s efficiency while by taking PAs nonidealities into account we extracted the new equations to find the conditions to improve the efficiency compared to conventional zero current and zero current switching conditions. The PA efficiency is equal to 79.5% while having 30dBm output power. The mixer alongside power amplifier used in this work provide a conversion gain of 9 dB while having 16 dBm output compression point. The  employed tunable quadrature oscillator has the ability to cancel phase and amplitude errors without comprimising the oscillator phase noise. The transmitter reaches an efficiency of 73.4% and an EVM of -32.75 dB.

Design of a High Range, High Efficiency Spread Spectrum Transmitter for Audio Communication Applications